Peak Flood & Time of Concentration

Estimate peak discharge with the Rational Method using MERIT-Hydro delineation and IDF-based rainfall intensity

Analysis Controls

Provide coordinates manually or click directly on the map to set the outlet point.

Peak flow will be estimated for this design storm.
How to Use
  1. Click a point on the map, or switch to Manual Entry and type coordinates
  2. Choose the IDF dataset and design return period
  3. Click "Run Analysis" to delineate the catchment and estimate peak discharge
  4. Review the assumptions, or re-run with your own runoff/intensity values
Analysis Results

Select an outlet point and click "Run Analysis" to view results

Peak Discharge Estimate
-- Return Period
-- m³/s
Q = 0.278 · C · I · A
Q = 0.278 × C × I × A
Time of Concentration (Tc) -- hrs
Runoff Coefficient (C) --
Rainfall Intensity (I) -- mm/hr
Catchment Area (A) -- km²
Longest Flow Path
Flow Length (L) 0.00 km
Headwater Elev. (H_start) 0.0 m
Outlet Elev. (H_outlet) 0.0 m
Elev. Difference (ΔH) 0.0 m
Slope (S) 0.0000 m/m (0.00%)

Want to test your own assumptions? Change any runoff coefficient or the rainfall intensity below, then click Re-run with My Values. This only recalculates the peak discharge

Runoff Coefficient (C) by Land Cover
--
Each row below is a land-cover type found in this catchment, with the coefficient currently applied to it (0 = no runoff, 1 = all rainfall becomes runoff). Edit any value to test a different assumption.
Applied to any part of the catchment the land-cover map couldn't classify.
Rainfall Intensity (I)
Auto-calculated from the IDF dataset at the time of concentration. Override this to test a different design-storm intensity.

This is how the estimate above was calculated — the method, data source, and formula behind each number.

Time of Concentration
--
Rainfall (IDF Dataset)
--
Rational Method Formula
Q = 0.278 · C · I · A
    Data Sources & Provenance
    • Elevation & Delineation: MERIT-Hydro (Multi-Error-Removed Improved-Terrain Hydrography) at 3 arc-second (~90 m) resolution. It corrects striping and tree canopy errors on MERIT DEM and HydroSHEDS to trace D8 flow directions and watershed boundaries.
    • Land Use / Land Cover (LULC): National Remote Sensing Centre (NRSC), ISRO 1:250,000 scale LULC map (2023-24) using an 18-class scheme. Weighted calculations are processed using a Cloud-Optimized GeoTIFF in its native Albers Conic Equal Area projection (56 m pixels).
    • Runoff Coefficients (C): Default coefficients are mapped based on standard Indian Rational Method practice (adapted from IRC:SP / IS 4987 lookup tables and Central Water Commission design-flood guidance) corresponding to the LULC cover types.
    • Rainfall Intensity-Duration-Frequency (IDF): Derived from:
      • ERA5: ECMWF global climate reanalysis providing hourly historic rainfall.
      • IMDAA: Indian Monsoon Data Assimilation and Analysis high-resolution regional reanalysis.
      • BCC-CSM2-MR: Beijing Climate Center projection model for future climate scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5).

    Inputs, results, charts, LULC map & land-cover distribution, tables, equations, methodology, assumptions & limitations. Opens in a new tab — use Print / Save as PDF.

    Processing Delineation...
    Analyzing flow paths on MERIT raster grids.