Provisional. 10 assumptions carried this answer and a person has accepted 0 of them. What that means is under the figures.
[OVERRIDDEN] 1 value changed by a person.
[LAND COVER CHOSEN] A person chose the land cover treatment for 14.2 percent of the existing site (2.705 ac): Woody wetlands, curve number supplied by the engineer.
[SOIL CHOSEN] A person chose the soil group for 16 percent of the site.
Each mark is repeated beside the figures it affects and set out in full under them.
Runoff summary
This is an increase, not a reduction. The proposed condition produces 185,557 cu ft (4.260 ac-ft) more runoff than the existing condition at the 9.20 in design storm, 78.1 percent of the existing runoff volume. Runoff depth is 2.677 in more (78.1 percent of the existing depth).
Existing runoff depth
3.427 in [OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Proposed runoff depth
6.104 in [OVERRIDDEN][LAND COVER CHOSEN]
Existing runoff volume
237,571 cu ft (5.454 ac-ft) [OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Proposed runoff volume
423,128 cu ft (9.714 ac-ft) [OVERRIDDEN][LAND COVER CHOSEN]
Change in runoff depth, proposed less existing
+2.677 in, an increase [OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Change in runoff volume, proposed less existing
+185,557 cu ft (4.260 ac-ft), an increase [OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Increase, share of the existing runoff volume
78.1 percent
Existing peak
39.07 cfs
Proposed peak
90.60 cfs
Change in peak, proposed less existing
+51.53 cfs, an increase
Peaks by the NRCS Delmarva dimensionless unit hydrograph (peak rate factor 284).
Site map
Site boundary Site boundary 19.098 ac, centroid at latitude 38.671250, longitude -75.460400. North is up. Imagery: USGS The National Map, public domain, flown June 2, 2023.
The report below qualifies these figures.
[OVERRIDDEN] 1 value changed by a person. 1 value in force was changed by a person from the derived, table or default value. Each one, with its reason, is in the overrides section.
[LAND COVER CHOSEN] A person chose the land cover treatment for 14.2 percent of the existing site (2.705 ac): Woody wetlands, curve number supplied by the engineer. The datasets name no TR-55 row for this ground, so the treatment and its curve number were answered on the derived data panel by CurveNumber Examples. Reason given: “Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after”. Each one is in the overrides section.
[SOIL CHOSEN] A person chose the soil group for 16 percent of the site. Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (16.2 percent): published B/D, used D. Who chose it and why is in the soils table and the overrides section.
These are the report's own findings, quoted from it. They are printed here because a recipient of this address reads the summary above before the report below, and a figure read without them is read without the thing that says what it is a comparison of.
Provisional: assumptions not acknowledged. 10 assumptions carried this answer and a person has accepted 0 of them. 10 carry no acceptance, so this report is provisional. Provisional means the figures on this page were computed and are not withheld, and that no licensed person had yet put their name to every assumption underneath them. This count was read at Sep 26, 2026, 7:23 PM EDT and is frozen here: acknowledgments recorded after that do not reach this copy. This copy was published on Sep 26, 2026, 7:23 PM EDT. The figures on this page were computed at Sep 26, 2026, 6:51 PM EDT, which is the run this publication is of and is not the moment it was published.
An acceptance on this report is an account holder submitting one, at the time printed with it. This product does not verify professional licensure: it holds no license number and no state of licensure, and it records no evidence that an entry was read as distinct from accepted. An acceptance is not a seal, a signature or a certification, and the absence of one is not a finding that anything is wrong.
Compared with an earlier submittal
Figure
Earlier run report CNR-7C8B9C521817 9.2 in, 24.0 hr, NRCS Type II computed Sep 26, 2026, 6:50 PM EDT
This run report CNR-2E6A2352B9EC 9.2 in, 24.0 hr, NRCS Type II computed Sep 26, 2026, 6:51 PM EDT
existing runoff depth
3.427 in
3.427 in
proposed runoff depth
6.104 in
6.104 in
existing runoff volume
237,571 cu ft
237,571 cu ft
proposed runoff volume
423,128 cu ft
423,128 cu ft
existing peak discharge
60.43 cfs
39.07 cfs
proposed peak discharge
127.53 cfs
90.60 cfs
These are the figures each run reported, at the same storm. They are the figures on the two reports.
The figures above reproduce the selected run. They are a summary and not the analysis: what they rest on, what CurveNumber refused and what nobody has checked is in the report below, and a figure quoted out of this page without it is a figure quoted without its qualifications.
Anybody who has this address can open it. No account, no sign-in and no password is needed, so treat the address itself as the control.
CNR-2E6A2352B9ECFarm field to warehouse, Georgetown areaCurveNumber 0.9.0
Published at https://app.curvenumber.com/p/3qCqHE8T_0fWinS0P38FeX9LQeFz6b8x. Computational aid only. Not an engineering deliverable or a certification of compliance. Requires review by a qualified professional.
This copy of report CNR-2E6A2352B9EC is published at https://app.curvenumber.com/p/3qCqHE8T_0fWinS0P38FeX9LQeFz6b8x. Open that address to compare this printout with the published document.
Reports are shown as they print, on a light page.
CurveNumber
Runoff report
Report CNR-2E6A2352B9EC
Inputs CNI-A3CCE7D80A9B
Computed Sep 26, 2026, 6:51 PM EDT
Version CurveNumber 0.9.0
Status PROVISIONAL, read at Sep 26, 2026, 7:23 PM EDT
Farm field to warehouse, Georgetown area
Example 3: Special rainfall and hydrograph cases, client Example clients (fictional), jurisdiction Sussex County, Delaware. Prepared by CurveNumber Examples, CurveNumber, as entered by the account holder.
Located in Sussex County, Delaware (boundary centroid at latitude, longitude 38.6713, -75.4604).
Site boundary Site boundary 19.098 ac, centroid at latitude 38.671250, longitude -75.460400. North is up. Imagery: USGS The National Map, public domain, flown June 2, 2023.
This result rests on
[OVERRIDDEN] 1 value changed by a person.1 value in force was changed by a person from the derived, table or default value. Each one, with its reason, is in the overrides section.
[LAND COVER CHOSEN] A person chose the land cover treatment for 14.2 percent of the existing site (2.705 ac): Woody wetlands, curve number supplied by the engineer.The datasets name no TR-55 row for this ground, so the treatment and its curve number were answered on the derived data panel by CurveNumber Examples. Reason given: “Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after”. Each one is in the overrides section.
[SOIL CHOSEN] A person chose the soil group for 16 percent of the site.Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (16.2 percent): published B/D, used D. Who chose it and why is in the soils table and the overrides section.
The marks in square brackets are repeated beside the figures they affect. Each item is set out in full directly after the headline figures.
Read this before the figures
This report was produced using CurveNumber.com, a computational aid for estimating NRCS curve numbers and direct runoff. It is not an engineering deliverable and it is not a certification of compliance with any regulation, ordinance, or design standard. The curve number method, as published in USDA NRCS Technical Release 55 and National Engineering Handbook Part 630 Chapter 10, is an empirical method with substantial uncertainty, and its applicability to any specific site is a professional judgment that this software has not made. Input data were retrieved from third party sources listed at https://curvenumber.com/data-sources and are provided by those sources without warranty. All results require review, verification, and adoption by a qualified professional before use in design, permitting, or construction. CurveNumber.com is not the engineer of record for any project.
No Data Quality Grade is stated on this report. The grade is a defined measure of how good the inputs behind a result are, this version does not compute one, and an absent grade is not a good grade. What this report carries instead is the provenance of each input individually, in the dataset and assumption sections below.
185,557 cu ft[OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Increase in runoff volume, existing against proposed, at the 9.20 in design storm: 4.260 ac-ft, 78.1 percent of the existing runoff volume. Runoff depth rises by 2.677 in (78.1 percent of the existing depth).
This is an increase, not a reduction. The proposed condition produces more runoff than the existing condition at this storm.
Existing depth
3.427 in [OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Proposed depth
6.104 in [OVERRIDDEN][LAND COVER CHOSEN]
Existing volume
237,571 cu ft (5.454 ac-ft) [OVERRIDDEN][LAND COVER CHOSEN][SOIL CHOSEN]
Proposed volume
423,128 cu ft (9.714 ac-ft) [OVERRIDDEN][LAND COVER CHOSEN]
Design storm 9.20 in over 24.0 hr, NRCS Type II. Peak discharge by the NRCS Delmarva dimensionless unit hydrograph (peak rate factor 284): existing 39.07 cfs; proposed 90.60 cfs. [TC BASIS DIFFERS] The existing Tc is CurveNumber's estimate and the proposed Tc was entered by the engineer. Part of the change in peak may come from how each time of concentration was found rather than from the development. Enter both, or use CurveNumber's estimate for both, to compare like with like.
Summary, page 2: what was entered
Condition
Area
Acres
Soil group
CN
Cover
Existing
Pasture, grassland or range, fair condition, soil A, from land cover Grassland/herbaceous
5.679
A
49.0
Pasture, grassland or range, Fair
Existing
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil A, from land cover Shrub/scrub
5.062
A
35.0
Brush, brush-weed-grass mixture with brush the major element, Fair
Existing
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil B, from land cover Shrub/scrub
3.256
B
56.0
Brush, brush-weed-grass mixture with brush the major element, Fair
Existing
Woods, fair condition, soil B, from land cover Evergreen forest
0.801
B
60.0
Woods, Fair
Existing
Pasture, grassland or range, fair condition, soil B, from land cover Grassland/herbaceous
0.568
B
69.0
Pasture, grassland or range, Fair
Existing
Woods, fair condition, soil D, from land cover Evergreen forest
0.644
D
79.0
Woods, Fair
Existing
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil D, from land cover Shrub/scrub
0.383
D
77.0
Brush, brush-weed-grass mixture with brush the major element, Fair
Existing
Woody wetlands, curve number supplied by the engineer, soil group B
0.641
B
77.0 [LAND COVER CHOSEN]
No TR-55 table row; curve number chosen by a person
Existing
Woody wetlands, curve number supplied by the engineer, soil group D
2.064
D
77.0 [LAND COVER CHOSEN]
No TR-55 table row; curve number chosen by a person
Proposed
Warehouse roof and truck court, on group A
6.500
A
98.0
Impervious, paved and roofed
Proposed
Warehouse parking and drives, on group B
1.500
B
98.0
Impervious, paved and roofed
Proposed
Woods, fair condition, soil D, from land cover Evergreen forest
0.644
D
79.0
Woods, Fair
Proposed
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil D, from land cover Shrub/scrub
0.383
D
77.0
Brush, brush-weed-grass mixture with brush the major element, Fair
Proposed
Lawn and landscaping, good condition, on group A
4.241
A
39.0
Open space, Good
Proposed
Lawn and landscaping, good condition, on group B
3.125
B
61.0
Open space, Good
Proposed
Woody wetlands, curve number supplied by the engineer, soil group B
0.641
B
77.0
No table row; curve number entered
Proposed
Woody wetlands, curve number supplied by the engineer, soil group D
2.064
D
77.0
No table row; curve number entered
Time of concentration used: existing 0.388 hr (23.3 min) (CurveNumber's estimate); proposed 0.250 hr (15.0 min) (entered by the engineer). Tc basis differs: the existing Tc is CurveNumber's estimate and the proposed Tc was entered by the engineer. Part of the change in peak may come from how each time of concentration was found rather than from the development. Enter both, or use CurveNumber's estimate for both, to compare like with like.
No practice is on this run.
Summary, page 3: what a person changed, and why
CN, Woody wetlands, curve number supplied by the engineer, soil group B: set to 77 CN. By CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT. Reason given: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after.
CN, Woody wetlands, curve number supplied by the engineer, soil group D: set to 77 CN. By CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT. Reason given: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after.
Soil group on Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded: published B/D, used D. By CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT. Reason given: Observed on site: Site walk on 2026-09-12 (fictional survey for this example) found no drain tile, no outlet ditches and standing water in the low ground along the stream. The Longmarsh and Indiantown soils are left undrained, so group D governs, which is also the conservative choice for runoff.
Design storm return period: set to 100 yr. By CurveNumber Examples on Sep 26, 2026, 6:48 PM EDT. Reason given: Delaware Sediment and Stormwater Regulations (7 DE Admin. Code 5101), flooding event: the 100-year, 24-hour storm, checked for this example site in Sussex County.
Proposed time of concentration: entered as 0.250 hr for this run, in place of CurveNumber's estimate of 0.411 hr. Typed on the Compute form; no reason is asked for a run input.
The full record follows this summary, unchanged: every section, with each figure's source.
The full record
What this result rests on, in full
[OVERRIDDEN] 1 value changed by a person. 1 value in force was changed by a person from the derived, table or default value. Each one, with its reason, is in the overrides section.
[LAND COVER CHOSEN] A person chose the land cover treatment for 14.2 percent of the existing site (2.705 ac): Woody wetlands, curve number supplied by the engineer. The datasets name no TR-55 row for this ground, so the treatment and its curve number were answered on the derived data panel by CurveNumber Examples. Reason given: “Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after”. Each one is in the overrides section.
[SOIL CHOSEN] A person chose the soil group for 16 percent of the site. Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (16.2 percent): published B/D, used D. Who chose it and why is in the soils table and the overrides section.
Existing and proposed both total 19.098 ac; they differ by 6 sq ft (0.00 percent), which is within the 0.095 ac tolerance and is shown as information, not as a finding.
Volumes and peaks are computed over the areas entered: 19.098 ac existing and 19.098 ac proposed. The drawn boundary is 19.098 ac. Land cover and soil were read from 30 m map squares. Each square counts only for the part of it inside your boundary, so the derived areas are shares of the 19.098 ac you drew. Your boundary is about 85.9 of those squares. The areas total 19.098 ac.
Woody wetlands, 2.705 ac: computed with curve number 77 supplied by the engineer. Chosen by CurveNumber Examples. Reason: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after.
Land cover folded into a larger class on its soil group (each below CurveNumber's minimum share for a class of its own; waiving the fold keeps each class at its own share): On soil group A, 0.050 ac of Evergreen forest (0.5% of that group) was folded into Grassland/herbaceous, so its CN 36 is computed as CN 49. On soil group B, 0.219 ac of Mixed forest (4.2% of that group) was folded into Shrub/scrub, so its CN 60 is computed as CN 56. On soil group D, 0.003 ac of Mixed forest (0.1% of that group) was folded into Evergreen forest; both are CN 79, so the site figure does not change.
The state and county named by the datasets were compared with every geographic statement typed onto this file, and they agree.
Provisional: assumptions not accepted
10 assumptions carried this answer and a person has accepted 0 of them. 10 carry no acceptance, so this report is provisional.
Provisional means that the figures on this report were computed and are not withheld, and that the account holder has not yet submitted an acceptance of every assumption underneath them. The assumptions are listed further down with what each one is worth in the answer and what evidence would displace it.
8 of the 10 outstanding are an entry for which CurveNumber's list of default values states that no external source exists, or which it rates Low confidence. Those are accepted one at a time, cannot be accepted in bulk, and each one asks for a written reason.
An acceptance on this report is an account holder submitting one, at the time printed with it. This product does not verify professional licensure: it holds no license number and no state of licensure, and it records no evidence that an entry was read as distinct from accepted. An acceptance is not a seal, a signature or a certification, and the absence of one is not a finding that anything is wrong.
This count is as of , when this copy of the page was produced. It can change after that; the report identifier does not, because it names the computation. Two printouts with the same identifier are the same computation; if their counts differ, the later one is current.
An entry is accepted on its own when it has no published source (a judgment, or a threshold CurveNumber chose) or when its confidence is low. Every other entry (a method constant, a published table, a local manual's figure or a research value rated moderate or better) may be accepted together with others in one act, and the record says so.
Site map
Site boundary Site boundary 19.098 ac, centroid at latitude 38.671250, longitude -75.460400. North is up. Imagery: USGS The National Map, public domain, flown June 2, 2023.
The boundary is the one saved on this site when it was computed, and the practice footprint is the one drawn for the practice, if any. The aerial photograph was taken from the public service when this report was made and is kept with the report, so it shows the ground as it was photographed, not as it is today. The map is for locating the site; the areas on this report are the figures, not measurements off this picture.
Where this site is
Quantity
Value
Boundary centroid
latitude 38.671250, longitude -75.460400
Boundary extent
north 38.672500, south 38.670000, east -75.458800, west -75.462000
Enclosed area
19.098 ac
Coordinate reference system
WGS84 decimal degrees (EPSG:4326), longitude first
Boundary vertices
4
This boundary was drawn or loaded on the map. It was NOT geocoded: this product does not turn an address into an area of interest, because the Census geocoder returns a point interpolated along a street centerline and runoff computed around such a point is runoff for a piece of road. The coordinates below are the polygon a person drew, and every dataset on this report was read over that polygon and over nothing else.
The boundary every dataset on this report was read over
#
Longitude
Latitude
#
Longitude
Latitude
#
Longitude
Latitude
1
-75.462000
38.670000
2
-75.458800
38.670000
3
-75.458800
38.672500
4
-75.462000
38.672500
What is claimed about this ground, and on whose evidence
Statement
Value
Source
Basis
Checked
State
Delaware
USDA NRCS SSURGO survey area DE005
read from a federal dataset over this boundary
CHECKED
The first two characters of a survey area symbol are the postal code of the state the survey area is administered under. The soil groups on this report were read from DE005 over the boundary above.
State
Delaware
US Census Bureau geocoder, geographies at the boundary centroid
looked up from the boundary's own coordinate
CHECKED
Sussex County, Delaware, read from US Census Geocoder (current boundaries) at -75.460400, 38.671250. This is the county and state whose published boundaries contain that one point, not a statement about the whole site.
County
Sussex County
US Census Bureau geocoder, geographies at the boundary centroid
looked up from the boundary's own coordinate
CHECKED
The county whose published boundary contains the centroid -75.460400, 38.671250. A site straddling a county line lies in two counties and this names the one its middle falls in. It is where the ground is and not a statement about which authority reviews the application.
Region
Ohio River Basin and Surrounding States
NOAA Atlas 14 Volume 2
read from a federal dataset over this boundary
CHECKED
This volume is published for a region rather than for one state, and the states it covers are delineated on a map this product does not hold. It names the region the site is in and makes no claim about which state.
Annual NLCD Land Cover (CONUS) 2024: A national map is sampled at this boundary's own coordinates, so it agrees with the boundary whatever the boundary is and is not evidence about where the boundary is.
The curve number method, chosen by the storm depth rule: Judged area by area on each area's own curve number: P of 9.2 in is above 2 Ia on every area that yields a material share of the runoff. The curve number governs, with a mandatory sensitivity band. Sensitivity: A five CN unit uncertainty either way on every area's curve number moves the site's area weighted runoff at this depth from 2.84 in to 4.03 in, against 3.43 in as computed, a factor of 1.4 from end to end.
Method by area. Each area is judged on its own curve number and initial abstraction (TR-55 Chapter 2); impervious cover is computed at its TR-55 curve number. The site figure is the area weighted mean of the runoff depths below.
Condition
Area
Acres
CN
Ia, in
Runoff, in
Method
Existing
Pasture, grassland or range, fair condition, soil A, from land cover Grassland/herbaceous
5.679
49.0
2.082
2.89
curve number, with a sensitivity band
Existing
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil A, from land cover Shrub/scrub
5.062
35.0
3.714
1.25
curve number, with a sensitivity band
Existing
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil B, from land cover Shrub/scrub
3.256
56.0
1.571
3.76
curve number, standard
Existing
Woods, fair condition, soil B, from land cover Evergreen forest
0.801
60.0
1.333
4.26
curve number, standard
Existing
Pasture, grassland or range, fair condition, soil B, from land cover Grassland/herbaceous
0.568
69.0
0.899
5.39
curve number, standard
Existing
Woods, fair condition, soil D, from land cover Evergreen forest
0.644
79.0
0.532
6.63
curve number, standard
Existing
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil D, from land cover Shrub/scrub
0.383
77.0
0.597
6.39
curve number, standard
Existing
Woody wetlands, curve number supplied by the engineer, soil group B
0.641
77.0
0.597
6.39
curve number, standard
Existing
Woody wetlands, curve number supplied by the engineer, soil group D
2.064
77.0
0.597
6.39
curve number, standard
Proposed
Warehouse roof and truck court, on group A
6.500
98.0
0.041
8.96
curve number, standard
Proposed
Warehouse parking and drives, on group B
1.500
98.0
0.041
8.96
curve number, standard
Proposed
Woods, fair condition, soil D, from land cover Evergreen forest
0.644
79.0
0.532
6.63
curve number, standard
Proposed
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil D, from land cover Shrub/scrub
0.383
77.0
0.597
6.39
curve number, standard
Proposed
Lawn and landscaping, good condition, on group A
4.241
39.0
3.128
1.70
curve number, with a sensitivity band
Proposed
Lawn and landscaping, good condition, on group B
3.125
61.0
1.279
4.38
curve number, standard
Proposed
Woody wetlands, curve number supplied by the engineer, soil group B
0.641
77.0
0.597
6.39
curve number, standard
Proposed
Woody wetlands, curve number supplied by the engineer, soil group D
2.064
77.0
0.597
6.39
curve number, standard
Storm
Quantity
Value
Note
Design storm depth
9.20 in
derived The site's design storm estimate. NOAA Atlas 14 (Volume 2 Version 3) 24-hr duration, 100 year ARI, mean estimate, partial duration series, Ohio River Basin retrieved . The depth this run was computed at is the design storm estimate in force on this site, so that estimate's own provenance is published here: it is the same value the estimates panel shows, quoted rather than recomputed. Whether the return period behind it is the one the governing requirement asks for is a regulatory choice this product does not make.
Duration
24.0 hr
The curve number method has no rainfall intensity term. The duration is recorded because it governs the Green-Ampt path and because a reviewer will ask for it, not because it changes a curve number result.
Initial abstraction ratio, lambda
0.20
CurveNumber's default initial abstraction ratio, which applies where nothing replaces it. No saved abstraction setting on this site replaced it for this run. Its source and what it is worth are in the assumptions section below.
Tc basis differs
NRCS unit hydrograph peak, lag = 0.6 Tc (NEH Part 630, Chapter 16). Unit hydrograph: the NRCS Delmarva dimensionless unit hydrograph (peak rate factor 284), because the site is on the Delmarva coastal plain (Delaware and the Eastern Shore counties of Maryland and Virginia, less the Piedmont north of the Fall Line). Ordinates from Maryland Stormwater Design Manual, Volume II (Maryland Department of the Environment, 2000) Appendix D.14, Table D.14.2, 24-Hour Dimensionless Unit Hydrograph for Use in the Delmarva Peninsula (NRCS Delmarva unit hydrograph, Welle, Woodward and Moody 1980), not yet checked by a second person. The site with no practice on it, under the NRCS Type II storm distribution, which was chosen for this run; its fit to this region was not assessed. Time of concentration used: existing 0.388 hr (23.3 min) (CurveNumber's estimate); proposed 0.250 hr (15.0 min) (entered by the engineer). Tc basis differs. The existing Tc is CurveNumber's estimate and the proposed Tc was entered by the engineer. Part of the change in peak may come from how each time of concentration was found rather than from the development. Enter both, or use CurveNumber's estimate for both, to compare like with like. Time step 0.05 hr existing and 0.025 hr proposed, each set from its own time of concentration. The peak is built from runoff computed for each area separately and added (distributed). A hand check at the composite curve number gives a lower peak where impervious and pervious areas are mixed, which TR-55 itself warns a composite understates. A practice's effect on the peak is shown with the practice, and the note on the distribution table below applies to its routed peaks too.
Condition
Peak
Time to peak
Existing
39.07 cfs
12.15 hr
Proposed
90.60 cfs
12.08 hr
Change, proposed against existing
an increase of 51.53 cfs
Distribution: NRCS Type II, chosen for this run. TR-55 Figure B-2 assigns the NRCS type by county; this product does not hold that map, so the choice has not been checked against it.
Not checked against the source The NRCS Delmarva dimensionless unit hydrograph ordinates were copied from Maryland Stormwater Design Manual, Volume II (Maryland Department of the Environment, 2000) and have not had a second person's check. The NRCS Type II rainfall distribution was read from the published NRCS table by script and has not yet had a second person's check.
The four NRCS 24 hour distributions in this product are the published NRCS tables at a 0.1 hour step (as issued with WinTR-55 version 2.00), read from the published files by a script and compared by machine with a second copy of the same tables. They have NOT yet had a second person's check against the NRCS program files. This matters more here than a curve number would: a distribution ordinate changes the peak intensity, and the peak intensity drives the inflow hydrograph, the stage the practice reaches and therefore the volume split reported below. Where the jurisdiction publishes its own distribution, supply it.
The datasets these areas were read from
This section is the record for this report: the editions it read and the dates they were read. Every dataset CurveNumber reads, with the edition in use, is listed at https://curvenumber.com/data-sources. A dataset's retrieved date can be earlier than the day the areas were read. CurveNumber keeps a copy of each answer a publisher's service gives it, and a later request for the same map tile, soil survey area or storm point is answered from that copy rather than from the publisher again. The read date is when this site's areas were read; the retrieved date is when CurveNumber fetched that answer from the publisher, and the edition printed with it is the one that answer carries.
Dataset
Value
What it means here
Land cover product
Annual NLCD Land Cover (CONUS)
Edition year 2024. Native resolution 30 m, 900 m² the pixel.
Map squares over this site
n = 85.9
The boundary equals 85.9 map squares. 109 squares touch it, each counted for the part inside it. The note under this table says what n tells a reader.
Map square count
At least 10
Enough map squares for CurveNumber not to warn that the land cover is coarse for this site. That is a floor and not a grade.
Impervious fraction
Read off the fractional impervious map
A measured per pixel percentage on the same grid and the same year as the classes, not a class midpoint.
Impervious citation
Annual NLCD Fractional Impervious Surface (CONUS) (Annual NLCD Fractional Impervious Surface (CONUS), 2024, 30 m, EPSG:5070 native grid) 109 pixels at 30 m retrieved
Land cover citation
Annual NLCD Land Cover (CONUS) (Annual NLCD Land Cover (CONUS), 2024, 30 m, EPSG:5070 native grid) retrieved
Soil survey areas
DE005 (DE005 v26 )
Each survey area publishes its own edition. A site crossing two of them stands on two editions, and a hydrologic soil group read from one is not the same claim as the same letter read from the other.
Map units
3
Distinct soil map unit polygons inside the boundary. The minimum site area rule treats this count as the soils equivalent of a pixel count.
Map units the survey rates a hydrologic soil group for
3 of 3
Every map unit inside this boundary carries a published hydrologic soil group. Mapped ground and rated ground are the same ground here.
Soil map units
Map unit
Share of site
Published group
Group used
How it was decided
Rosedale loamy sand, 0 to 2 percent slopes (RoA), survey area DE005
56.2%
A
A
As published.
Hammonton loamy sand, 0 to 2 percent slopes, Northern Tidewater Area (HmAd), survey area DE005
27.6%
B
B
As published.
Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (LO), survey area DE005
16.2%
B/D
Doverridden
Group D, answered by CurveNumber Examples; the default was the undrained letter D; reason: Observed on site: Site walk on 2026-09-12 (fictional survey for this example) found no drain tile, no outlet ditches and standing water in the low ground along the stream. The Longmarsh and Indiantown soils are left undrained, so group D governs, which is also the conservative choice for runoff.
Soils citation
USDA NRCS SSURGO via Soil Data Access (SSURGO, DE005 v26 ) retrieved
Area of interest
19.10 ac
Geodesic area of the derived boundary. This is the denominator in n above.
n is the boundary's area measured in land cover map squares: the area divided by the area of one square. Every square that touches the boundary is counted only for the part of it inside, so the derived areas add up to the boundary. n says how many independent readings of the ground the land cover rests on; a site of a few squares is coarse for this dataset whatever its areas add up to.
What the datasets said about themselves.
3 land cover classes were folded into a larger class on the same soil group, because each was smaller than one 30 m land cover pixel (0.222 ac) on that soil group, below what the map resolves: On soil group A, 0.050 ac of Evergreen forest (0.5% of that group) was folded into Grassland/herbaceous, so its CN 36 is computed as CN 49. On soil group B, 0.219 ac of Mixed forest (4.2% of that group) was folded into Shrub/scrub, so its CN 60 is computed as CN 56. On soil group D, 0.003 ac of Mixed forest (0.1% of that group) was folded into Evergreen forest; both are CN 79, so the site figure does not change. Waiving the fold keeps every class at its own share.
CurveNumber raised no refusal on either condition or on a practice during this run. That is a statement about this run and not a warranty: a refusal is raised where a named condition is met, and the conditions CurveNumber tests are the ones in its list of refusals.
Both aggregation paths
Aggregation path
Existing
Proposed
Change, proposed less existing
What it is
Distributed (reported)
3.4270 in
6.1036 in
+2.6766 in, increase
Runoff computed on each area, then area weighted.
Composite
3.3944 in
6.1123 in
+2.7179 in, increase
Curve number area weighted, then runoff computed once. This is what a hand check produces.
Composite curve number
53.1
74.8
Area weighted.
Divergence, composite less distributed
-0.95 percent
0.14 percent
Signed. The direction reverses between small and large storms, so the sign is reported rather than a direction asserted.
The two paths differ because runoff is a non-linear function of the curve number, so averaging the curve numbers first and averaging the runoff first do not give the same answer; the distributed path is reported because it applies the method to each surface as the method was fitted, and the composite path is printed beside it because it is what a reviewer recomputing by hand from a single area weighted curve number will obtain.
What was estimated, from what, and what each estimate is worth
Check these 3 first: temporal distribution, a factor of 8.37 on peak one hour rainfall fraction; slope, a factor of 6.70 on slope across the area; time of concentration, a factor of 5.32 on time of concentration. The other 5 move their own figures by a factor of 4.00 or less and are reported rather than put in front of you.
RANK 1 HEADLINE Temporal distribution derived
0.277 fraction of total depth
Can change the peak one hour rainfall fraction by up to 8.4 times.
Rests on: NOAA Atlas 14 Volume 2 Version 2.1 temporal distribution file for Volume 2 (Ohio River Basin and Surrounding States), area general, 24h duration, fetched and hashed rather than transcribed. WHICH of its 45 curves is a judgment and is CurveNumber's default value “Which of the NOAA Atlas 14 quartile cases and probability of occurrence lines a design storm shape is taken from”.
The selection spans a factor of 5.10 on the peak one hour fraction inside this file, and a factor of 8.37 against the NRCS Type II curve the product uses without it. The volume is untouched.
Displaced by: The quartile case and probability line the governing jurisdiction names, which supersedes outright. Failing that, NOAA's own guidance on which case a design should use, which is published alongside the files and which this product has not read. A local gauge record of the storms that actually produced the design flows displaces the whole question.
NOAA Atlas 14 (Volume 2 Version 2.1) first quartile case, 10 percent cumulative probability of occurrence line, 24h duration, Volume 2 (Ohio River Basin and Surrounding States), area general retrieved
RANK 2 HEADLINE Slope of the receiving area derived
1.02 percent
Can change the slope across the area by up to 6.7 times.
Rests on: USGS 3DEP (1 m DEM, acquired ) Slope Degrees raster function retrieved . Median of 2304 sampled pixels, in percent, which is the tangent of the angle and not the angle.
The site spans P10 0.38 to P90 2.54 percent, a factor of 6.70, around a median of 1.02. A maximum slope condition is decided conservatively by the P90 and a minimum slope condition by the P10, and no single number is conservative for both, so the median is reported with both beside it.
Displaced by: A graded surface from the plan, which is what the credit is actually checked against: the slope that matters is the one the receiving area will have after construction, and a DEM measures the one it has now.
USGS 3DEP (1 m DEM, acquired ) Slope Degrees raster function retrieved
RANK 3 HEADLINE Time of concentration computed
0.388 hr
Can change the time of concentration by up to 5.3 times.
Rests on: TR-55 segmental: sheet flow over range, natural at n = 0.13 for 100 ft, then shallow concentrated flow. Slope 1.02 percent from USGS 3DEP, two year 24 hour depth 3.41 in from NOAA Atlas 14 Volume 2 Version 3, flow length 1290 ft estimated as the longest chord of the drawn boundary, which is not a flow path.
The surface is worth a factor of 5.32 on Tc and decides whether the peak discharge is drawn at the TR-55 minimum; the sheet flow cap 1.58; the estimated flow length 1.20.
Displaced by: The flow path drawn on the grading plan, measured from the hydraulically most distant point to the design point, which is what the method actually asks for and what no dataset contains. A LiDAR flow accumulation routing over the graded surface displaces it too and is not implemented.
Computed here from the figures named above. There is no external source because nothing external was read for it.
RANK 4 Irrigation water demand defaulted
10,007 cu ft/day
Can change the irrigation demand in the governing month by up to 4.0 times.
CurveNumber default value (“Plant factor in a landscape water budget”), which is an assumption and not a measurement.
RANK 5 Antecedent dry period derived
11 days
Can change the antecedent dry period by up to 2.8 times.
NOAA NCEI GHCN-Daily (station record through ) station USC00075320, 90th percentile of interevent dry period length retrieved
RANK 6 Green roof evapotranspiration rate defaulted
0.13 in/day
Can change the green roof recovery time by up to 2.5 times.
CurveNumber default value (“Ratio of an extensive green roof's evapotranspiration to the grass reference”), which is an assumption and not a measurement.
RANK 7 Contributing flow path length defaulted
1,290 ft
Can change the contributing flow path length by up to 1.4 times.
CurveNumber default value (“Which geometric bound is offered for a jurisdictional credit measurement”), which is an assumption and not a measurement.
RANK 8 Design storm depth derived
9.2 in
Can change the design storm depth at a named return period by up to 1.2 times.
NOAA Atlas 14 (Volume 2 Version 3) 24-hr duration, 100 year ARI, mean estimate, partial duration series, Ohio River Basin retrieved
Design storm return period SUPPLIED
100 yr
Supplied by CurveNumber Examples on , and CurveNumber recomputed from it. Nothing was overwritten: this is an argument CurveNumber takes, not a value it produced. It is an override all the same, because a person put it into this report, and it is in the overrides section below with every other one.
Reason: Delaware Sediment and Stormwater Regulations (7 DE Admin. Code 5101), flooding event: the 100-year, 24-hour storm, checked for this example site in Sussex County.
Receiving flow path length NOT OFFERED
DELIBERATELY LEFT BLANK. A bound computable from the site boundary would make the condition easier to satisfy, so the field stays empty, the condition comes back unchecked and the credit is denied.
Receiving flow path length: the length of pervious ground the flow crosses, which is a dimension of a practice nobody has drawn yet and not a dimension of the site. The narrowest crossing of the site boundary is a bounding dimension and using it here would credit a disconnection across ground that may hold no disconnection at all. The field is left empty, so a condition reading it comes back unchecked and the credit is not granted, which is the correct outcome.
Filter strip width NOT OFFERED
DELIBERATELY LEFT BLANK. A bound computable from the site boundary would make the condition easier to satisfy, so the field stays empty, the condition comes back unchecked and the credit is denied.
Width: the width of a filter strip measured across the face it treats, which needs the flow direction and the strip, and CurveNumber has neither. A bounding dimension of the site is not a strip width. The field is left empty and a condition reading it denies the credit.
Indoor water demand NO DATASET
NOT IN ANY DATASET THIS PRODUCT READS. There is nothing to estimate from and a plausible figure would be an invention.
An indoor water demand cannot be estimated from anything this product reads: it depends on occupancy, which no dataset holds. The irrigation part of a cistern's demand is estimated; the indoor part is not, because a guessed continuous demand would give a cistern its whole credit on a number nobody supplied. To credit it, enter a metered monthly demand schedule with a written commitment that the use continues.
Overrides of the derived and defaulted values
dual group B/D on map unit Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (LO) overridden
hydrologic soil group decision recorded; the letter used for each map unit is in the soil map unit table in the datasets section
Replaced by a later entry for the same quantity, listed below. This row is history and is not the value this report was computed from.
Not recorded against any one area: this override is against the site.
Changed by CurveNumber Examples on Sep 26, 2026, 6:45 PM EDT, CurveNumber's default value “Dual hydrologic soil group resolution”
Reason given: Observed on site: Site walk on 2026-09-12 (fictional survey for this example) found no drain tile, no outlet ditches and standing water in the low ground along the stream. The Longmarsh and Indiantown soils are left undrained, so group D governs, which is also the conservative choice for runoff.
CN, Woody wetlands, curve number supplied by the engineer, soil group B overridden
set to 77 CN
On the existing condition, area Woody wetlands, curve number supplied by the engineer, soil group B.
Changed by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT
Reason given: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after.
CN, Woody wetlands, curve number supplied by the engineer, soil group D overridden
set to 77 CN
On the existing condition, area Woody wetlands, curve number supplied by the engineer, soil group D.
Changed by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT
Reason given: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after.
dual group B/D on map unit Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (LO) overridden
hydrologic soil group decision recorded; the letter used for each map unit is in the soil map unit table in the datasets section
Not recorded against any one area: this override is against the site.
Changed by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT, CurveNumber's default value “Dual hydrologic soil group resolution”
Reason given: Observed on site: Site walk on 2026-09-12 (fictional survey for this example) found no drain tile, no outlet ditches and standing water in the low ground along the stream. The Longmarsh and Indiantown soils are left undrained, so group D governs, which is also the conservative choice for runoff.
Design storm return period supplied
set to 100 yr
A person supplied this input and CurveNumber recomputed the estimate from it. Nothing was overwritten: the figure it displaced is CurveNumber’s own, and it is printed with the estimates above.
Not recorded against any one area: this override is against the site.
Supplied by CurveNumber Examples on Sep 26, 2026, 6:48 PM EDT
Reason given: Delaware Sediment and Stormwater Regulations (7 DE Admin. Code 5101), flooding event: the 100-year, 24-hour storm, checked for this example site in Sussex County.
Records that are not overrides. The product wrote these when a condition was copied, or they are the design of a practice.
Proposed condition seeded from existing by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT: 19.098 ac copied. Nothing copied has been edited since, so the surfaces are the same in both conditions and any change is the practice.
The aerial photograph, and what was read off it
No aerial photograph of this site was classified.
Nothing on this report rests on an aerial photograph. This is the ordinary case and it is stated rather than left to be inferred from the absence of a section, because a page that does not mention imagery and a page that says no photograph was classified read identically and mean different things.
The curve number fitted to an observed record, and what it is about
No curve number was fitted to an observed record for this site.
Nothing on this report rests on a gauged rainfall and discharge record. This is the ordinary case and it is stated rather than left to be inferred from the absence of a section. It is also the expected case: a curve number fitted at a stream gauge describes the whole watershed above that gauge, and this product will not print such a figure against a site that is not inside that watershed and a large enough fraction of it, which most sites are not.
Refusals a supplied input resolved
No refusal was resolved by a supplied input.
Nothing on this report rests on a figure a user handed CurveNumber to answer a refusal with. Where a refusal fired, it fired and it is printed as a refusal.
Refusals a person waived
No refusal was waived.
Every figure on this report is one CurveNumber produced. Nobody waived a refusal, and no figure here rests on a signature in place of a computation.
The assumptions that carry this answer
Hydrologic condition defaultedFair (a judgment with no published source; low confidence)
PENDINGno acceptance recorded
Worth in the answer: 5 to 12 CN units. One of the two largest silent levers in the method.
Displaced by: A site visit, current aerial imagery, or a measured ground cover fraction against the NEH Chapter 9 mapping.
Curve number suppression band, lower defaulted2 multiples of Ia (a threshold CurveNumber chose; low confidence)
PENDINGno acceptance recorded
Worth in the answer: A five CN unit uncertainty is worth a factor of 18.1 at 1.5 Ia, 4.4 at 2 Ia, 2.3 at 3 Ia and 1.4 at 9 Ia.
Displaced by: Expert panel calibration.
Curve number caution band, upper defaulted5 multiples of Ia (a threshold CurveNumber chose; low confidence)
PENDINGno acceptance recorded
Worth in the answer: Above this the method is in the regime it was fitted for.
Displaced by: Expert panel calibration.
Impervious connectivity defaulted0 (a judgment with no published source; low confidence)
PENDINGno acceptance recorded
Worth in the answer: Bounded at 10.2 CN units. Figure 2-4 adjusts the composite as CN = CNp + (Pimp/100)(98 - CNp)(1 - R/2), so the whole span from fully connected to fully unconnected is 0.5 (Pimp/100)(98 - CNp), largest at the 30 percent total impervious ceiling the figure is valid to and at the lowest pervious curve number TR-55 publishes, which is 30: 0.15 x 68 = 10.2 units. At a pervious CN of 61 the same bound is 5.55 units, and at 80 it is 2.7.
Displaced by: A delineated drainage path showing impervious area discharging to pervious ground. Automated detection from LiDAR routing is an open gap.
Cover type, NLCD 71 grassland and herbaceous defaultedPasture, grassland or range, Fair (a judgment with no published source; low confidence)
PENDINGno acceptance recorded
Worth in the answer: 21 CN units on group B and 38 on group A across the range this one class spans. Pasture in poor condition is 79 on group B against meadow at 58, which is 1.189 in against 0.274 in, a factor of 4.3; on group A it is 68 against 30, 0.627 in against exactly zero.
Displaced by: Imagery or a site visit distinguishing mown, grazed and unmanaged grass, which is the distinction TR-55 prices and NLCD does not record.
Cover type, NLCD 52 shrub and scrub defaultedBrush, brush-weed-grass mixture with brush the major element, Fair (a judgment with no published source; low confidence)
PENDINGno acceptance recorded
Worth in the answer: 16 CN units on group B against the desert shrub row that is right for the same class in the arid west: brush Fair 56 against desert shrub Fair 72, which is 0.220 in against 0.808 in, a factor of 3.7. On group A it is 35 against 55, exactly zero against 0.195 in.
Displaced by: A user naming the vegetation displaces it directly. The site's location already moves it: since round one of the 2026 review the crosswalk is given the site's coordinates, and west of the 100th meridian (outside the humid Pacific coast north of 40 degrees) class 52 maps to desert shrub, Table 2-2d, stated as an assumption on the result.
4 further default values applied to this computation and are left out here, because a reader shown thirty defaults checks none of them. Those above are ordered by the strength of the evidence behind them, weakest first. The complete list, with what each is worth and what would replace it, is on the Reference page of CurveNumber. Across all 10 of them, 0 have been acknowledged and 10 have not; the machine readable companion to this report lists every one with its state.
Assumptions with no external source
These values carry the answer and nothing external supports them: some are judgments for which no source exists at all (a judgment with no published source), and others are product thresholds that were reasoned rather than measured (a threshold CurveNumber chose). They are assumptions, recorded as assumptions. The text below is CurveNumber's own statement of each value, verbatim.
Hydrologic condition defaultedFair (a judgment with no published source)
NO EXTERNAL SOURCE EXISTS. Fair is the mid-range assignment and avoids systematic bias. Recorded as a judgment, not a citation, because a user told this is 'the published default' will not think to change it, and a user told it is a mid-range assumption worth 5 to 12 CN units will.
Worth in the answer: 5 to 12 CN units. One of the two largest silent levers in the method.
Displaced by: A site visit, current aerial imagery, or a measured ground cover fraction against the NEH Chapter 9 mapping.
Curve number suppression band, lower defaulted2 multiples of Ia (a threshold CurveNumber chose)
REASONED, NOT MEASURED. Proposed default awaiting calibration.
Worth in the answer: A five CN unit uncertainty is worth a factor of 18.1 at 1.5 Ia, 4.4 at 2 Ia, 2.3 at 3 Ia and 1.4 at 9 Ia.
Displaced by: Expert panel calibration.
Curve number caution band, upper defaulted5 multiples of Ia (a threshold CurveNumber chose)
REASONED, NOT MEASURED.
Worth in the answer: Above this the method is in the regime it was fitted for.
Displaced by: Expert panel calibration.
Impervious connectivity defaulted0 (a judgment with no published source)
NO EXTERNAL SOURCE EXISTS. The conservative assumption.
Worth in the answer: Bounded at 10.2 CN units. Figure 2-4 adjusts the composite as CN = CNp + (Pimp/100)(98 - CNp)(1 - R/2), so the whole span from fully connected to fully unconnected is 0.5 (Pimp/100)(98 - CNp), largest at the 30 percent total impervious ceiling the figure is valid to and at the lowest pervious curve number TR-55 publishes, which is 30: 0.15 x 68 = 10.2 units. At a pervious CN of 61 the same bound is 5.55 units, and at 80 it is 2.7.
Displaced by: A delineated drainage path showing impervious area discharging to pervious ground. Automated detection from LiDAR routing is an open gap.
Cover type, NLCD 71 grassland and herbaceous defaultedPasture, grassland or range, Fair (a judgment with no published source)
NO EXTERNAL SOURCE EXISTS. This is the row the land cover reader names as the reason the crosswalk is a judgment rather than a lookup: the same code covers a mown lawn, an unmanaged old field and a hayfield. Maps to pasture with the condition left to “Hydrologic condition”, which is the middle of that range rather than an assertion about the site.
Worth in the answer: 21 CN units on group B and 38 on group A across the range this one class spans. Pasture in poor condition is 79 on group B against meadow at 58, which is 1.189 in against 0.274 in, a factor of 4.3; on group A it is 68 against 30, 0.627 in against exactly zero.
Displaced by: Imagery or a site visit distinguishing mown, grazed and unmanaged grass, which is the distinction TR-55 prices and NLCD does not record.
Cover type, NLCD 52 shrub and scrub defaultedBrush, brush-weed-grass mixture with brush the major element, Fair (a judgment with no published source)
NO EXTERNAL SOURCE EXISTS, and this is the weakest row in the crosswalk. One class code covers eastern successional brush and western sagebrush and desert shrub, which TR-55 puts in different tables. Maps to brush, the humid region row, east of the 100th meridian, and to desert shrub in fair condition west of it; the meridian is a coordinate rule standing in for a climate map, not a measurement of the cover.
Worth in the answer: 16 CN units on group B against the desert shrub row that is right for the same class in the arid west: brush Fair 56 against desert shrub Fair 72, which is 0.220 in against 0.808 in, a factor of 3.7. On group A it is 35 against 55, exactly zero against 0.195 in.
Displaced by: A user naming the vegetation displaces it directly. The site's location already moves it: since round one of the 2026 review the crosswalk is given the site's coordinates, and west of the 100th meridian (outside the humid Pacific coast north of 40 degrees) class 52 maps to desert shrub, Table 2-2d, stated as an assumption on the result.
Dual hydrologic soil group resolution defaultedthe undrained letter (D) unless drainage is attested (a judgment with no published source)
NO EXTERNAL SOURCE EXISTS. The conservative choice, matching the physical condition absent evidence of drainage.
Worth in the answer: Enormous. Open space in good condition on A/D is CN 39 drained against CN 80 undrained. At P = 3 in, pasture on B against D is 0.365 in against 1.250 in, a factor of 3.42.
Displaced by: User attestation that artificial drainage is present, or a drain tile record.
Cover type, NLCD 41, 42 and 43 forest defaultedWoods, Fair (a judgment with no published source)
NO EXTERNAL SOURCE EXISTS. Classes 41, 42 and 43 all map to woods with the condition left to “Hydrologic condition”. What is lost is real and unrepresentable: evergreen canopy intercepts through the winter and deciduous litter changes with the season, and the method has no term for either.
Worth in the answer: The condition axis carries this mapping and the family does not. Woods Poor 66 against Good 55 on group B is 0.545 in against 0.195 in, a factor of 2.8; on group A it is 45 against 30, which is 0.024 in against exactly zero. Distinguishing deciduous from evergreen is worth nothing in this method, because there is one woods row.
Displaced by: Litter depth, canopy cover and evidence of grazing observed on site, read against the NEH Chapter 9 woods condition descriptions.
Inputs, for recomputation
Existing condition
Area
Area, ac
CN
Impervious, %
Provenance
Curve number basis
Pasture, grassland or range, fair condition, soil A, from land cover Grassland/herbaceous
5.679
49
0
derived
Pasture, grassland or range, Fair, hydrologic soil group A. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Pasture, grassland or range, fair condition, CN 49 for hydrologic soil group A. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil A, from land cover Shrub/scrub
5.062
35
0
derived
Brush, brush-weed-grass mixture with brush the major element, Fair, hydrologic soil group A. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Brush, brush-weed-grass mixture with brush the major element, fair condition, CN 35 for hydrologic soil group A. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil B, from land cover Shrub/scrub
3.256
56
0
derived
Brush, brush-weed-grass mixture with brush the major element, Fair, hydrologic soil group B. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Brush, brush-weed-grass mixture with brush the major element, fair condition, CN 56 for hydrologic soil group B. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Woods, fair condition, soil B, from land cover Evergreen forest
0.801
60
0
derived
Woods, Fair, hydrologic soil group B. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Woods, fair condition, CN 60 for hydrologic soil group B. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Pasture, grassland or range, fair condition, soil B, from land cover Grassland/herbaceous
0.568
69
0
derived
Pasture, grassland or range, Fair, hydrologic soil group B. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Pasture, grassland or range, fair condition, CN 69 for hydrologic soil group B. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Woods, fair condition, soil D, from land cover Evergreen forest
0.644
79
0
derived
Woods, Fair, hydrologic soil group D. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Woods, fair condition, CN 79 for hydrologic soil group D. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil D, from land cover Shrub/scrub
0.383
77
0
derived
Brush, brush-weed-grass mixture with brush the major element, Fair, hydrologic soil group D. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2c, Brush, brush-weed-grass mixture with brush the major element, fair condition, CN 77 for hydrologic soil group D. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Woody wetlands, curve number supplied by the engineer, soil group B
0.641
77
0
overridden
The datasets name no TR-55 row for this land cover; the treatment and curve number were chosen by CurveNumber Examples: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Woody wetlands, curve number supplied by the engineer, soil group D
2.064
77
0
overridden
The datasets name no TR-55 row for this land cover; the treatment and curve number were chosen by CurveNumber Examples: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after. Read from the public datasets on Sep 26, 2026, 6:46 PM EDT.
Proposed condition
Area
Area, ac
CN
Impervious, %
Provenance
Curve number basis
Warehouse roof and truck court, on group A
6.500
98
100
enteredCN derived
Impervious, paved and roofed, hydrologic soil group A. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2a, Impervious, paved and roofed, CN 98 for hydrologic soil group A. Area, cover and soil group typed by CurveNumber Examples on Sep 26, 2026, 6:48 PM EDT.
Warehouse parking and drives, on group B
1.500
98
100
enteredCN derived
Impervious, paved and roofed, hydrologic soil group B. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2a, Impervious, paved and roofed, CN 98 for hydrologic soil group B. Area, cover and soil group typed by CurveNumber Examples on Sep 26, 2026, 6:48 PM EDT.
Woods, fair condition, soil D, from land cover Evergreen forest
0.644
79
0
copied
Woods, Fair, hydrologic soil group D. TR-55 (1986) Table 2-2c, Woods, fair condition, CN 79 for hydrologic soil group D. Copied from the existing condition by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT; the area it was copied from was read from the datasets.
Brush, brush-weed-grass mixture with brush the major element, fair condition, soil D, from land cover Shrub/scrub
0.383
77
0
copied
Brush, brush-weed-grass mixture with brush the major element, Fair, hydrologic soil group D. TR-55 (1986) Table 2-2c, Brush, brush-weed-grass mixture with brush the major element, fair condition, CN 77 for hydrologic soil group D. Copied from the existing condition by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT; the area it was copied from was read from the datasets.
Lawn and landscaping, good condition, on group A
4.241
39
0
enteredCN derived
Open space, Good, hydrologic soil group A. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2a, Open space, good condition, CN 39 for hydrologic soil group A. Area, cover and soil group typed by CurveNumber Examples on Sep 26, 2026, 6:48 PM EDT.
Lawn and landscaping, good condition, on group B
3.125
61
0
enteredCN derived
Open space, Good, hydrologic soil group B. USDA NRCS TR-55 (1986, 2nd ed.) Table 2-2a, Open space, good condition, CN 61 for hydrologic soil group B. Area, cover and soil group typed by CurveNumber Examples on Sep 26, 2026, 6:48 PM EDT.
Woody wetlands, curve number supplied by the engineer, soil group B
0.641
77
0
copied
No cover class named; copied from the existing condition, where it was read from the datasets. Copied from the existing condition by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT; the area it was copied from was read from the datasets.
Woody wetlands, curve number supplied by the engineer, soil group D
2.064
77
0
copied
No cover class named; copied from the existing condition, where it was read from the datasets. Copied from the existing condition by CurveNumber Examples on Sep 26, 2026, 6:46 PM EDT; the area it was copied from was read from the datasets.
How to read the provenance marks
entereddouble borderA person typed this area: its area, and its cover and soil group where named. Who and when are printed on the row. Where the curve number is the TR-55 table value for that cover and soil group, the row also says the curve number was looked up; the area and the choice of cover are still the person's.editeddouble border, underlinedA person changed the area, cover, soil group or curve number of this area after it was derived, entered or copied. The change, who, when and the reason are printed on the row and in the overrides section.copiedheavy solid borderCopied from the other condition. The row says whether the area it was copied from was read from the datasets or typed by a person.derivedsolid borderRetrieved from a published source. The citation and its edition are printed with the value, because TR-55 1986 and TR-55 1975 disagree and a citation without an edition cannot be checked.defaulteddashed borderAn assumption, not a measurement. CurveNumber's list of default values entry is named, and what the assumption is worth in the answer is stated with it. Where no external source exists for the assumption, this report says so in those words.overriddendouble border, hatched, boldA person changed the value. Who, when, the prior value and the reason given are recorded in the overrides section and cannot be edited afterwards, because the parameter record is append only.supplieddouble border, boldA person gave CurveNumber an argument and it recomputed from it: a measured flow path length in place of the geometric bound, the flow surface the ground actually is, the month the design storm is taken in. Nothing the product had stored was overwritten, which is why this mark is not the override mark; what the argument displaced is CurveNumber's own figure, and the estimates section prints it. Who, when and the reason given are in the overrides section and the record is append only.accepteddouble border, dotted inner rule, boldA person examined a figure a machine produced and adopted it unchanged. It carries a person's mark because a person put it into this record under their own name, and it is not the supplied mark because nothing was handed to anything and nothing recomputed: the magnitude is the machine's own. Two acts carry it. The acceptance of a classification of an aerial photograph, which is a guess about an image and not a measurement of the ground, and which the imagery section explains; and the acceptance of a curve number fitted to a gauged rainfall and discharge record, which is a property of the whole watershed above that gauge and not a measurement of this site, and which the calibration section explains. The mark is also on an area of ground the soil survey does not rate, computed on the most likely soil group a person accepted (an estimate, not a survey rating), and on an impervious area sized by an accepted photograph. Who, when and the reason given are in the overrides section and the record is append only.fitteddashed border, dotted inner ruleCurveNumber fitted this magnitude to an observed record. It carries no person's mark, because no person put it here, and it is not the computed mark, because a computed value is a function of the inputs printed beside it and a fitted one is a function of the inputs AND of conventions: change the baseflow separation and not one input moves while the magnitude moves by curve number units. It is never printed without its interval, and a fitted figure becomes an input to a design only when a named person accepts it, which is a separate act carrying the accepted mark above.
The marks are separated by the word, by the border style and by the fill, in that order of reliability, so this report can be read correctly from a black and white photocopy and from a browser printing with background graphics switched off.
Reproducibility
Item
Value
Report identifier
CNR-2E6A2352B9EC
Inputs fingerprint
CNI-A3CCE7D80A9B
Report format version
16
Run identifier
run_fe6a1b12313dbd36
Computed at
Report document built at
This copy rendered at
CurveNumber version
0.9.0
Times on this report
The site's local time: Eastern Time (America/New_York). Found from the site's location in the U.S. Department of Transportation's time zone boundaries (Bureau of Transportation Statistics, updated Jan 5, 2023), stored with CurveNumber.
Identifier basis
The report identifier is a SHA-256 hash of the run identifier, CurveNumber version, the storm, the method badge, the headline figures and the area table. It excludes the generation time, so re-rendering an unchanged run reproduces the same identifier. IT ALSO EXCLUDES THE ACKNOWLEDGMENT STATE, which is not a property of the run: who has accepted which assumption is a record of what people have done since, it is read afresh every time this document is rendered, and the instant it was read is printed with it in the status line above and under the count on page one. Two printouts bearing this identifier are the same computation over the same inputs. Where their acceptance counts differ, they were read at the two times printed on them and neither figure has moved. The identifier cannot be checked against a printout alone: an edited copy can carry it. To verify a printout, ask the applicant for the published link, which serves the same document from this product. The inputs fingerprint beside the identifier is a hash of the inputs alone, so two runs of the same inputs share it.
Decision support. Every figure in this report requires independent verification, and a licensed professional is responsible for the design. Values marked DERIVED carry a citation with an edition. Values marked DEFAULTED carry an assumption rather than a measurement, and for some of them no external source exists, which CurveNumber's list of default values states on its face and which this report repeats rather than hides. Values marked OVERRIDDEN were changed by a named person, and the prior value and the reason given are printed in the overrides section.
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Steps and their effect
Before the first run (steps 1 to 26). No run existed yet, so these steps were not priced. The first run is priced against the storm it was computed at.
1. Created the site Farm field to warehouse, Georgetown area.
by CurveNumber Examples, Sep 26, 2026, 6:42 PM EDT
2. Set the site boundary at 19.092 ac.
by CurveNumber Examples, Sep 26, 2026, 6:42 PM EDT
3. Moved the site boundary from 19.092 to 19.098 ac; it is on different ground: none of the new boundary lies inside the old one.
by CurveNumber Examples, Sep 26, 2026, 6:42 PM EDT
4. Derived 7 areas over a 19.098 ac boundary from the published datasets; the areas total 16.392 ac, and refused a headline number: “Water or wetland covers part of the site and has no TR-55 curve number”.
by CurveNumber Examples, Sep 26, 2026, 6:43 PM EDT
14.2% of the site is land cover with no TR-55 row that has not been answered, so no single number is produced for the site until it is. Woody wetlands: 2.705 ac (14.2% of the site) is in no area yet. TR-55 has no wetland row. Supply a curve number from your local manual, choose the TR-55 row you want used, or leave the wetland out of the drainage area as storage. To proceed: answer each piece of ground: for water, rain on the water surface runs off (CN 98) or the water is left out of the drainage area as storage; for wetlands, a curve number from the local manual, a chosen TR-55 row, or leaving it out as storage. Waiving reports the headline over the rest of the site with the unanswered ground stated beside it.
Steps 5, 6, 7, 8, 9, 10, 11. Estimates CurveNumber recorded for this site
by CurveNumber Examples, Sep 26, 2026, 6:43 PM EDT
Derived temporal distribution at 0.277 of the total depth
Derived slope of the receiving area at 1.016 percent
Computed time of concentration at 0.388 hr
Defaulted irrigation water demand at 10,007 cu ft/day
Derived antecedent dry period at 11 days
Defaulted green roof evapotranspiration rate at 0.13 in/day
Defaulted contributing flow path length at 1289.882 ft
Each is an input some practices and credits use. The report's estimates section says what each rests on and whether this run used it.
12. Attested hydrologic soil group D for map unit Longmarsh and Indiantown soils, 0 to 1 percent slopes, frequently flooded (LO).
by CurveNumber Examples, Sep 26, 2026, 6:45 PM EDT
An attestation supplies an input and moves no figure by itself. The next reading of the public data uses it and shows what it was worth.
13. Derived 7 areas over a 19.098 ac boundary from the published datasets, replacing 7; the areas total 16.392 ac, and refused a headline number: “Water or wetland covers part of the site and has no TR-55 curve number”.
by CurveNumber Examples, Sep 26, 2026, 6:45 PM EDT
14.2% of the site is land cover with no TR-55 row that has not been answered, so no single number is produced for the site until it is. Woody wetlands: 2.705 ac (14.2% of the site) is in no area yet. TR-55 has no wetland row. Supply a curve number from your local manual, choose the TR-55 row you want used, or leave the wetland out of the drainage area as storage. To proceed: answer each piece of ground: for water, rain on the water surface runs off (CN 98) or the water is left out of the drainage area as storage; for wetlands, a curve number from the local manual, a chosen TR-55 row, or leaving it out as storage. Waiving reports the headline over the rest of the site with the unanswered ground stated beside it.
14. Answered woody wetlands as curve number 77 supplied by the engineer.
by CurveNumber Examples, Sep 26, 2026, 6:46 PM EDT
Reason given:Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after.
The reason given: Wetland taken as woods, good condition, on a hydric soil (group D): TR-55 Table 2-2c, CN 77. The forested wetland along the stream is mapped as a buffer and stays untouched in both conditions, so the same number is used before and after. It is stored with the site and applied every time the public data is read, until it is withdrawn or no longer applies.
15. Derived 9 areas over a 19.098 ac boundary from the published datasets, replacing 7.
by CurveNumber Examples, Sep 26, 2026, 6:46 PM EDT
16. Seeded the proposed condition from the existing, 9 areas and 19.098 ac.
by CurveNumber Examples, Sep 26, 2026, 6:46 PM EDT
17. Removed area Pasture, grassland or range, fair condition, soil A, from land cover Grassland/herbaceous from the proposed condition, 5.679 ac at CN 49.
by CurveNumber Examples, Sep 26, 2026, 6:47 PM EDT
18. Removed area Brush, brush-weed-grass mixture with brush the major element, fair condition, soil A, from land cover Shrub/scrub from the proposed condition, 5.062 ac at CN 35.
by CurveNumber Examples, Sep 26, 2026, 6:47 PM EDT
19. Removed area Brush, brush-weed-grass mixture with brush the major element, fair condition, soil B, from land cover Shrub/scrub from the proposed condition, 3.256 ac at CN 56.
by CurveNumber Examples, Sep 26, 2026, 6:47 PM EDT
20. Removed area Woods, fair condition, soil B, from land cover Evergreen forest from the proposed condition, 0.801 ac at CN 60.
by CurveNumber Examples, Sep 26, 2026, 6:47 PM EDT
21. Removed area Pasture, grassland or range, fair condition, soil B, from land cover Grassland/herbaceous from the proposed condition, 0.568 ac at CN 69.
by CurveNumber Examples, Sep 26, 2026, 6:47 PM EDT
22. Added area Warehouse roof and truck court, on group A to the proposed condition, 6.500 ac at CN 98, impervious, paved and roofed.
by CurveNumber Examples, Sep 26, 2026, 6:48 PM EDT
23. Added area Warehouse parking and drives, on group B to the proposed condition, 1.500 ac at CN 98, impervious, paved and roofed.
by CurveNumber Examples, Sep 26, 2026, 6:48 PM EDT
24. Added area Lawn and landscaping, good condition, on group A to the proposed condition, 4.241 ac at CN 39, open space good.
by CurveNumber Examples, Sep 26, 2026, 6:48 PM EDT
25. Added area Lawn and landscaping, good condition, on group B to the proposed condition, 3.125 ac at CN 61, open space good.
by CurveNumber Examples, Sep 26, 2026, 6:48 PM EDT
26. Supplied design storm return period as 100 yr, which CurveNumber recomputed design storm depth from.
by CurveNumber Examples, Sep 26, 2026, 6:48 PM EDT
Reason given:Delaware Sediment and Stormwater Regulations (7 DE Admin. Code 5101), flooding event: the 100-year, 24-hour storm, checked for this example site in Sussex County.
27. Ran the site at the 9.2 in 24 hr storm by the curve number method.
by CurveNumber Examples, Sep 26, 2026, 6:49 PM EDT
Effect on the figures: At the 9.2 in storm this run moves runoff depth from 3.427 to 6.104 in, an increase of 78.1 percent, and volume from 237,571 to 423,128 cu ft, an increase of 78.1 percent.
28. Ran the site at the 9.2 in 24 hr storm by the curve number method.
by CurveNumber Examples, Sep 26, 2026, 6:50 PM EDT
Effect on the figures: At the 9.2 in storm this run moves runoff depth from 3.427 to 6.104 in, an increase of 78.1 percent, and volume from 237,571 to 423,128 cu ft, an increase of 78.1 percent.
29. Ran the site at the 9.2 in 24 hr storm by the curve number method.
by CurveNumber Examples, Sep 26, 2026, 6:51 PM EDT
Effect on the figures: At the 9.2 in storm this run moves runoff depth from 3.427 to 6.104 in, an increase of 78.1 percent, and volume from 237,571 to 423,128 cu ft, an increase of 78.1 percent.
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This document was produced with CurveNumber, which reads the soils, land cover, slope and design rainfall over a drawn boundary out of the public datasets and records what every figure rests on. The product is described at curvenumber.com. Nothing in this paragraph qualifies the figures above; what qualifies them is on the document itself. Every public dataset CurveNumber reads, with the edition in use, is listed on the data sources page.