Texas Curve Number Screening Map
Screening runoff curve numbers for any Texas address, coordinates, or site boundary.
Screening only — NRCS TR-55 values from national data under the assumptions you choose; not for design. Read the disclaimer.
Zipped shapefile (.shp, .shx, .dbf, and .prj), GeoJSON, or KML, up to 2,000 acres. Your file is read in your browser. Only a rectangle around the boundary is sent to the NRCS soil service (land cover loads from this site); HERO E&C does not receive or store your file.
Click the map to add corners. Click the first corner or press Finish boundary to close. Backspace removes the last corner; Esc cancels.
You can also click any point on the map. Zoom in to see curve numbers. Click the map, then scroll to zoom, or hold Ctrl and scroll; click outside the map to scroll the page. On a phone, use two fingers.
Assumptions fair · humid range (2-2c) · dual as D · unrated as D
Results
Search an address, enter coordinates, upload or draw a boundary, or click the map. Results appear here with the curve number, how it was assigned and a copyable worksheet.
How to read the results
- Curve number (CN)
- The NRCS runoff curve number, from about 30 to 98, describes how much of a storm becomes direct runoff for a soil and its cover. Higher numbers mean more runoff. The tool gives the value for average runoff condition (AMC II) with the standard initial abstraction, Ia = 0.2S.
- How a value is assigned
- Each NLCD land cover pixel (30 m data, stored at about 26 m) is paired with the NRCS hydrologic soil group at its center and given the TR-55 curve number for the cover type in the table below. Developed pixels use their own impervious share: CN = CNpervious + impervious share × (98 − CNpervious), with the pervious part as open space in good condition and the impervious part directly connected (TR-55 figure 2-3).
- Boundary results
- For an uploaded or drawn boundary, the worksheet lists acres and CN for each land cover and soil group pair, and the area-weighted curve number, Σ(CN × acres) ÷ Σ acres. You can copy it into a spreadsheet and replace any line with site data.
- Dual and unrated soil groups
- NRCS gives dual groups (A/D, B/D, C/D) to soils that are group D in their natural, undrained state; the first letter applies if the site is adequately drained (NRCS NEH Part 630, Chapter 7). Urban land, pits and water are often not rated. Choose how both are treated under Assumptions; the result lists the acres affected.
- Range and brush in West and South Texas
- TR-55 has two tables for range: Table 2-2c for humid regions and Table 2-2d for arid and semiarid rangelands. The page starts with Table 2-2c. Where Shrub/Scrub or Grassland is arid or semiarid range, as in much of West and South Texas, choose Table 2-2d under Assumptions; it gives higher curve numbers (desert shrub, fair, group B: 72 where Table 2-2c brush gives 56).
- Low curve numbers
- TR-55 says to use another procedure to determine runoff when the weighted curve number is less than 40. Woods or brush on group A soils can give such values.
- What it does not do
- The tool does not compute runoff depth, peak flow, time of concentration or detention, and it does not adjust for antecedent moisture other than AMC II or for disconnected impervious cover.
- Download data
- For a boundary, Worksheet (CSV) is the curve-number worksheet under the assumptions you chose, and Curve-number grid (GeoTIFF) holds the screening curve number of each pixel whose center is inside the boundary (WGS 84 grid of about 26 m; empty cells are −9999). Both say that the values are screening values, not design values. The files are made in your browser.
Land cover to TR-55 cover type
| NLCD class | Cover type used | CN for groups A / B / C / D |
|---|---|---|
| Open WaterNLCD 11 | Open water — taken as 98 (TR-55 has no water cover type; water surfaces are commonly treated like impervious area)HERO E&C assumption | 98 / 98 / 98 / 98 |
| Perennial Ice/SnowNLCD 12 | Perennial ice/snow — taken as 98HERO E&C assumption | 98 / 98 / 98 / 98 |
| Developed, Open SpaceNLCD 21 | Developed: impervious share at 98, the rest as open space in good condition (grass cover > 75%)TR-55 Table 2-2a | 98 × impervious share + open space (good) for the rest: A 39 / B 61 / C 74 / D 80 |
| Developed, Low IntensityNLCD 22 | Developed: impervious share at 98, the rest as open space in good condition (grass cover > 75%)TR-55 Table 2-2a | 98 × impervious share + open space (good) for the rest: A 39 / B 61 / C 74 / D 80 |
| Developed, Medium IntensityNLCD 23 | Developed: impervious share at 98, the rest as open space in good condition (grass cover > 75%)TR-55 Table 2-2a | 98 × impervious share + open space (good) for the rest: A 39 / B 61 / C 74 / D 80 |
| Developed, High IntensityNLCD 24 | Developed: impervious share at 98, the rest as open space in good condition (grass cover > 75%)TR-55 Table 2-2a | 98 × impervious share + open space (good) for the rest: A 39 / B 61 / C 74 / D 80 |
| Barren LandNLCD 31 | Newly graded areas (pervious, no vegetation) — HERO E&C pairing; NLCD barren land also includes rock outcrop, sand and beachesTR-55 Table 2-2a | 77 / 86 / 91 / 94 |
| Deciduous ForestNLCD 41 | WoodsTR-55 Table 2-2c | good: 30 / 55 / 70 / 77; fair: 36 / 60 / 73 / 79; poor: 45 / 66 / 77 / 83 |
| Evergreen ForestNLCD 42 | WoodsTR-55 Table 2-2c | good: 30 / 55 / 70 / 77; fair: 36 / 60 / 73 / 79; poor: 45 / 66 / 77 / 83 |
| Mixed ForestNLCD 43 | WoodsTR-55 Table 2-2c | good: 30 / 55 / 70 / 77; fair: 36 / 60 / 73 / 79; poor: 45 / 66 / 77 / 83 |
| Shrub/ScrubNLCD 52 | Brush — brush-weed-grass mixture with brush the major elementTR-55 Table 2-2c | good: 30 / 48 / 65 / 73; fair: 35 / 56 / 70 / 77; poor: 48 / 67 / 77 / 83 |
| Shrub/Scrub, arid or semiaridNLCD 52 · option | Desert shrub — saltbush, greasewood, creosotebush, blackbrush, bursage, palo verde, mesquite and cactusTR-55 Table 2-2d | good: 49 / 68 / 79 / 84; fair: 55 / 72 / 81 / 86; poor: 63 / 77 / 85 / 88 |
| Grassland/HerbaceousNLCD 71 | Pasture, grassland, or range — continuous forage for grazingTR-55 Table 2-2c | good: 39 / 61 / 74 / 80; fair: 49 / 69 / 79 / 84; poor: 68 / 79 / 86 / 89 |
| Grassland/Herbaceous, arid or semiaridNLCD 71 · option | Herbaceous — mixture of grass, weeds and low-growing brush, with brush the minor elementTR-55 Table 2-2d · Table 2-2d gives no group A value for herbaceous range; group A uses the Table 2-2c pasture value | good: – / 62 / 74 / 85; fair: – / 71 / 81 / 89; poor: – / 80 / 87 / 93 |
| Pasture/HayNLCD 81 | Pasture, grassland, or range — continuous forage for grazing (HERO E&C pairing; TR-55 meadow, mowed for hay, gives lower values)TR-55 Table 2-2c | good: 39 / 61 / 74 / 80; fair: 49 / 69 / 79 / 84; poor: 68 / 79 / 86 / 89 |
| Cultivated CropsNLCD 82 | Row crops, straight row (TR-55 gives good and poor values; fair uses poor)TR-55 Table 2-2b | good: 67 / 78 / 85 / 89; fair: 72 / 81 / 88 / 91; poor: 72 / 81 / 88 / 91 |
| Woody WetlandsNLCD 90 | Woods (TR-55 has no wetland cover type; wetland soils are often saturated, so runoff can be higher)TR-55 Table 2-2c | good: 30 / 55 / 70 / 77; fair: 36 / 60 / 73 / 79; poor: 45 / 66 / 77 / 83 |
| Emergent Herbaceous WetlandsNLCD 95 | Meadow — continuous grass (TR-55 has no wetland cover type; wetland soils are often saturated, so runoff can be higher)TR-55 Table 2-2c | 30 / 58 / 71 / 78 |
Curve numbers: USDA NRCS, Urban Hydrology for Small Watersheds, Technical Release 55 (210-VI-TR-55, Second Ed., June 1986), Tables 2-2a, 2-2b, 2-2c and 2-2d. TR-55 gives Table 2-2c for range in humid regions and Table 2-2d for arid and semiarid rangelands; choose under Assumptions. The pairing of NLCD classes with TR-55 cover types is HERO E&C’s screening assumption.
Known gaps
- Your city, county or TxDOT may require its own curve-number table, hydrologic condition or treatment of dual groups and impervious cover. Use the values your reviewing manual specifies.
- Annual NLCD 2025 is satellite land cover at 30 m, not a survey or a site plan. Development after 2025 is not shown, and small sites rest on few pixels.
- NLCD classes are paired with TR-55 cover types by assumption; TR-55 has no wetland or open-water cover type, and those rows are flagged.
- The soil group is the NRCS dominant condition for each map unit, not a site test. Map units mix soils that NRCS does not locate.
- Values are for AMC II. Runoff, peak flow and detention are not computed.
- Shrub/Scrub and Grassland start with TR-55 Table 2-2c (humid regions). For arid and semiarid range, choose Table 2-2d under Assumptions.
- Address search can place a point on the wrong side of a street. Check the marker, and click the correct spot on the map if needed.
- KMZ files are not supported yet; save the boundary as KML or GeoJSON.
- Opportunity pins mark the city or county named in the notice, not the project site; listings without a city or county have no pin.
Disclaimer
Informational screening only. This tool combines public NRCS SSURGO soil groups (Soil Data Access, read at the time shown) and USGS Annual NLCD 2025 land cover (stored on this site), with curve numbers from NRCS TR-55 under the assumptions shown. The curve numbers are screening estimates, not design values, a site investigation, or a sealed engineering document, and they have not been reviewed by a licensed professional for your property. Do not use them for design, construction, bidding, or permitting.
Local drainage criteria decide the curve-number table, the hydrologic condition and how soils and impervious cover are treated for a design. Confirm with a site survey, the soil survey and the reviewing engineer for your city or county.
Using this tool does not create an engineer–client relationship. Files you upload are read in your browser and are not uploaded; only the address you enter and the site location or a rectangle around the boundary are sent to the public services listed above to run the search. HERO E&C does not store your searches or files. HERO E&C · TBPELS Firm F-27793.
Data sources
| Layer | Source | Currency |
|---|---|---|
| Hydrologic soil groups | USDA NRCS SSURGO through Soil Data Access (public domain), dominant condition | Current soil survey versions; queried live |
| Land cover, impervious surface | USGS Annual National Land Cover Database (Annual NLCD) Collection 1.2 (public domain), prepared for Texas and stored on this site | Annual NLCD 2025 (released June 2026) |
| Curve numbers | USDA NRCS TR-55 (1986), Tables 2-2a, 2-2b, 2-2c | Second Edition, June 1986 |
| Basemaps | USGS The National Map (public domain) | As served by USGS |
| Address search | U.S. Census Bureau Geocoder | Current address ranges |
| Teaming opportunities | HERO E&C Teaming & Opportunities (/teaming/) and Construction Teaming (/construction/) listings | Updated with each listing review; pins at the city or county named in the notice |
Map software: ArcGIS Maps SDK for JavaScript. Powered by Esri. The soil groups and land cover behind each value are also on the Texas Soil Screening Map and the Texas Land Cover Screening Map.
Need more than a screening?
HERO E&C prepares drainage and floodplain studies, HEC-HMS / HEC-RAS models, and development permit applications across Texas.