Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 214

response time to peak runoff. As the infiltration opportunity time is decreased with
increasing slope, the total runoff volume is also increased.
6.5.2.5 Surface Depressions, Ponds, and Other Natural Water Storage
If the watershed contains much land depressions, ponds, and other detention storage,
the total runoff volume will certainly be decreased, and the time of concentration
will be increased.
6.5.2.6 Mulches and Crop Residues
Mulches and crop residues slow down the velocity of flow, thus allowing more
opportunity time for infiltration, and hence decrease the runoff volume.
6.5.2.7 Land Use
Land use is an important factor affecting peak runoff rate and runoff volume.
Vegetative and canopy pattern, surface roughness, mechanical soil disturbance,
amount of biomass in the surface and top layer, etc. affect water velocity, retention,
infiltration, and runoff rate and volume.
6.5.2.8 Soil Cover Management
Cover management practices affect both the forces applied to the soil by erosive
agents and the susceptibility of the soil to detachment. For a given land use like
cropland, important features include the crops that are grown, the type of tillage
system such as clean, reduced, or no till. Important features on a construction site
include whether or not the land is bare, mulch has been applied, the slope has been
recently reseeded, or the soil material is a cut or fill. Important features on range
and reclaimed land include the native or seeded vegetation and degree of ecological
maturity.
6.5.2.9 Other Management Practices
Support practices include ridging (e.g., contouring), vegetative strips and barriers
(e.g., buffer strips, strip cropping, fabric fence, gravel bags), runoff intercep-
tors (e.g., terraces, diversions), and small impoundments (e.g., sediment basins,
impoundment terraces).
6.5.3 Runoff Volume Estimation
Two general methods are available to compute runoff on small upland areas. The
first method is based on models such as Richards' equation or various approxi-
mations to it called infiltration equations. This method uses precipitation data as a