Design Flood Hydrograph

CWC Synthetic Unit Hydrograph Method & Hydrograph Routing

Utmost care has been taken in the digitisation and extraction of factors and formulas from the CWC Flood Estimation Reports (FER); even so, errors may occur. Users are advised to cross-check the factors, formulas and assumptions against the source reports before use in design.

1
Catchment Inputs
2
Unit Hydrograph
3
Flood Hydrograph

Catchment Characteristics

Set an outlet point and have the catchment characteristics derived for you, or enter them directly. These parameters are used to derive the Synthetic Unit Hydrograph from the CWC sub-zonal regression equations.

Derive from an outlet point

Click the outlet on the map, or type its coordinates. The catchment is delineated on the MERIT-Hydro grid and the area, main stream length, centroidal length, equivalent stream slope and CWC sub-zone are filled in below — every one of them still editable.

Physical Parameters
km²
Area must be a positive number.
km
Length must be a positive number.
km
Centroid length must be positive.
m/km
Slope must be positive.
CWC Sub-Zone Selection
Please select a CWC Sub-Zone.

When you derive from an outlet point, the sub-zone is set to whichever one holds the largest share of the delineated catchment — not the one the outlet alone falls in. Choose it here to override, or if you are entering the parameters by hand.

The Synthetic Unit Hydrograph is derived from these inputs alone. You will configure the design storm on the next step.

Click the outlet point on the map. After deriving, the delineated catchment, the traced main stream and the centroid are drawn here so you can check them before accepting the parameters.

Source: MERIT-Hydro flow direction and accumulation grids (3 arc-second), with elevations sampled from the MERIT digital elevation model.

Hydrometeorological homogeneous subzones as per CWC. Click the map to open the interactive viewer, where you can zoom in and out and drag to pan.

CWC Homogeneous Subzones Map Thumbnail
Click to Zoom & Pan
Source: MANUAL ON ESTIMATION OF DESIGN FLOOD, March 2001, by Hydrology Studies Organisation, Central Water Commision.