Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 207

applicable in subdivision developments on hilly or rolling topography. Lot benching
will reduce the slope and length of slope of disturbed areas, thereby reducing the
erosion potential. This practice also establishes drainage patterns on individual lots
within a subdivision at the time of rough grading.
Lot benching can be very effective for controlling erosion on hilly developments.
By reducing slope lengths and the steepness of slopes, the potential for erosion
is lowered. The amount of benefit derived from this practice depends upon the
steepness of the slopes and the erodibility of soils on the site.
6.4.5.2 Cutting and Filling
This operation is typically performed by tractors pulling dirt buckets or scrapers
that pick up soil in high points in a field and deposit it in low points in the field.
Dirt scraping operations are controlled by laser equipment that enables the slope of
a field to be cut to a specific grade. In some cases, the final operations of precision
grading would be to use a land leveler to smooth the graded field surface.
Several land grading methods are considered to be conservation practices by the
Natural Resources Conservation Service of the US Department of Agriculture. Land
smoothing (NRCS, code 466) is the practice of removing irregularities on the land
surface by use of special equipment. This practice is classified as rough grading and
does not require the use of a complete grid survey or other soil engineering data. The
purpose of this practice is to improve surface drainage, provide for more effective
use of precipitation, obtain more uniform planting depths, provide for more uniform
cultivation, improve equipment operation and efficiency, and facilitate contour cul-
tivation. Precision land forming (NRCS, code 462) is the practice of reshaping the
surface of land to planned grades. All land-forming operations under this practice
are performed on the basis of detailed engineering survey and layout. The purpose
of this practice is similar to that of land smoothing, primarily focused on improving
surface drainage. Irrigation land leveling (NRCS, code 464) is a conservation prac-
tice very similar to precision land forming. The major distinction is that the practice
of irrigation land leveling is performed for the primary purpose of increasing surface
irrigation efficiency.
Specific soil engineering practices related to the design and construction of
surface drainage systems on agricultural lands can be used to improve field
drainage. These practices are designed to improve the construction and mainte-
nance of agricultural surface drainage systems, which are adapted to modern farm
mechanization.
6.4.5.3 Construction Guidelines
Land to be graded should be cleared of brush and excessive crop residue, trash, or
vegetative material. Grading should not be attempted when soil moisture exceeds
that permitting normal tillage or plowing.
Bring the land to design grade or grades in accordance with a detailed plan
showing cuts, fills, and grades. Fills of more than 15 cm should be built up by
spreading the soil in successive layers. Disk or chisel the field surface after scoop