I need to calculate the overland flow of a catchment area. I have HEC HMS software but I don't want to use it. I need a mathematical equation.
TOPMODEL is used most often to predict the saturated-excess overland flow. It is based on calculating a groundwater table height that, when it intercepts the soil surface, will result in runoff.
Yes, methods like Manning's Equation, Rational Method, Topographic Analysis and Hydrologic Modeling can be employed. You need some level of expertise in hydraulic engineering to help you implement these method conveniently.@
Area of Cross-Section and Velocity as Observed at Bridge Site:
The area of cross-section is measured by taking a series of levels of the river at H.F.L. at certain intervals. The velocity in this case is determined at site by direct measurement of the velocity in place of theoretical calculation from bed slope etc.
To measure the velocity directly, the river is divided into few sections width wise and then the velocity for each section is determined by surface float placed at the centre of each section.
The time taken by the float to cover a fixed distance is noted by a stop watch and the distance travelled by the float divided by the time taken is the surface velocity of the stream. Such surface velocity is to be determined for each section and weightage average value is obtained for the purpose of flood discharge estimation.
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The velocity is least in the vicinity of the bed and banks and mean at the centre line of the stream at a point 0.3 d below the surface where, d, is the depth of water (see Fig. 3.6). If V, is the velocity at surface, Vb is the velocity at bottom and Vm is the mean velocity then their relationship may be established in the following equation,
Vm = 0.7 Vs= 1.3 Vb (3.15)
After the determination of the mean velocity of the stream, the flood discharge is obtained by;
Q = AVm (3.16)
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