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[Description] |
RATIONALE
RAINFLO is an online deterministic/conceptual distributed rainfall-runoff model suited for the simulation of flood flows. It is effective, accurate, and friendly. Try it and judge it for yourself.
The model has three major features:
- Hydrologic abstraction with the NRCS runoff curve number,
- Rainfall-runoff transform by convolution of the NRCS unit hydrograph with the effective storm hyetograph, and
- Stream channel routing with the Muskingum-Cunge method.
Abstraction with the runoff curve number is justified when the soil strata is subject to filling during an infrequent storm. The method limits the total infiltration depth, and therein lies its inherent strength. Other abstraction methods typically provide infinite infiltration depths. The conceptual basis of the curve number method is at the root of its wide applicability. It is the method of choice for practical applications worldwide.
The rainfall-runoff transform uses the NRCS unit hydrograph, which has built-in a small amount of runoff diffusion. This hydrograph is applicable to most field conditions, particularly when land slopes exceed 1%. The lumped character of the unit hydrograph produces a certain amount of diffusion which mimics the actual diffusion existing in nature.
The Muskingum-Cunge method is an analog of the diffusion wave model of surface runoff hydrodynamics. Given the proper set of physical and numerical parameters, the computational method is essentially grid independent, a necessary condition for accuracy of a routing scheme. In the linear mode, the model conserves mass exactly. In the nonlinear mode, the steepening or flattening of the flood hydrograph can be simulated, albeit at the cost of a relative small loss of mass.