Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 226

control measures as possible may provide the most effective erosion and sedimen-
tation control. The principles or strategies for erosion and sedimentation control are
summarized below:
(a) Reduce longitudinal slope (<3%) and length of run for furrows or borders
(b) Reduce the velocity of runoff water (e.g., by maintaining vegetative cover,
preserving vegetative buffer strip around the lower perimeter of the land
disturbance)
(c) Divert storm water runoff
(d) Practice minimum tillage or conservation tillage in erosive soil
(e) Use buffer strip, strip cropping, and gravel bags
(f) Provide runoff interceptors (e.g., terraces)
(g) Construct siltation basin/sediment basin at different points of the drainage
channel
(h) Apply organic/crop residues in the field which is prone to erosion
(i) Select land-use pattern (e.g., vegetative cover with crops) which minimizes rill
and gully erosion
(j) Increase the organic matter of soil to increase shear strength, thereby decrease
erosivity.
6.5.8 Modeling Runoff and Sediment Yield
Upland processes and processes in individual channel segments are combined
through the channel network and interchannel areas to influence runoff and sed-
iment yield from watersheds. In addition to the complex relationships on upland
areas in stream channels, processes affecting watershed runoff and sediment yield
include interactions (e.g., channel junctions and backwater) as well as land use,
soil and cover characteristics, and other factors varying over the drainage area. The
state-of-the-art in hydrology and erosion/sedimentation is such that runoff and sed-
iment yield from a watershed cannot be described adequately or predicted without
resorting to the use of indices, fitted parameters, and the application of judgment
and experience.
Erosion models play critical roles in soil and water resources conservation
and nonpoint source pollution assessments, including sediment load assessment
and inventory, conservation planning and design for sediment control, and for the
advancement of scientific understanding. The two primary types of erosion models
are process-based models and empirically based models. Process-based (physically
based) models mathematically describe the erosion processes of detachment, trans-
port, and deposition, and through the solutions of the equations describing those
processes provide estimates of soil loss and sediment yields from specified land sur-
face areas. Empirical models relate management and environmental factors directly
to soil loss and/or sediment yields through statistical relationships.