1Design Rainfall (IDF)

Search a place or coordinates, or click a point in Texas to pull live NOAA Atlas 14 data — or switch to manual entry.

Return period yr

Search or click a point in Texas to fetch its NOAA Atlas 14 (Vol. 11) point IDF.

Intensity by duration in/hr @ min

Intensity must decrease as duration increases; values 0–40 in/hr.

2Existing Conditions

The maximum allowable release Q(allow)

Existing Basin Runoff CoefficientC =–

Existing Basin Time of ConcentrationTc =min

Existing Basin AreaA =acres

Maximum Allowable RunoffQ(allow) =cfs

3Proposed Conditions

Proposed drainage area to the pond.

Proposed Basin Runoff CoefficientC =–

Proposed Basin Time of ConcentrationTc =min

Proposed Basin AreaA =acres

Method A · Triangular hydrograph

—acre-ft

Critical duration—

Method B · Trapezoidal hydrograph

—acre-ft

Critical duration—

Triangular · Modified Rational

Storage Critical inflow Linear outflow Q(allow)

Trapezoid · Modified Rational

Storage Inflow Outflow Q(allow)

Full routing tables · 1–180 min

4Recommended Preliminary Detention

Averaged triangular & trapezoidal storage for the 100‑yr and 2‑yr storms, then summed. Requires a map point so both return periods come from the same NOAA Atlas 14 cell.

Select a point on the map to populate this summary.

1 · Triangular storage · 100‑yr	—	acre‑ft
2 · Trapezoidal storage · 100‑yr	—	acre‑ft
3 · Average of 1 & 2	—	acre‑ft
4 · Triangular storage · 2‑yr	—	acre‑ft
5 · Trapezoidal storage · 2‑yr	—	acre‑ft
6 · Average of 4 & 5	—	acre‑ft