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Introuduction:


Land leveling or land grading for irrigation is modifying the surface relief of a field to a planned grade to provide a more suitable surface for efficiently applying irrigation water. Normally land leveling requires moving a lot of earth over several hundred meters.
This should not be confused with land planing, or land floating. They are usually accomplished with special equipment to eliminate minor irregularities, and they do not change the general topography of the land surface.
Rough grading is removing knolls, mounds, or ridges and filling pockets or swells in a field that is not to have a planned grade.  Often no construction stakes are set and reliance is placed on the "eye" of the equipment operator to obtain the desired field surface. Rough grading is seldom adequate for lands to be surface irrigated.


Criteria for land leveling:

Criteria for land leveling will be influenced by the soil, slope, climate, crops to be grown, methods of irrigation, and the desires of the farmer.
Land leveling should never be planned without knowing the soil profile conditions and the maximum cut that can be made without seriously affecting agricultural production. Shallow soils that require strict limitations on permissible depth of excavation do not permit much freedom to the designer. They pose a difficult problem when combined with undulating topography or steep slopes.

The climate of an area often places certain limits on slops to prevent erosion from rainfall or to provide adequate drainage. Also crops to be grown need to be known since they will affect the irrigation methods selected and will provide an idea as to the amount of leveling needed. Intensively cultivated crops such as vegetables may justify a high leveling cost whereas a hay crop in an area with a short growing season maul warrant a much smaller investment.
Each method of irrigation has limitations. When several methods of irrigation are to be used on the same field, the requirements of the most restrictive must be met. The level border method is the most restrictive of all irrigation methods. In general, flooding methods have the strictest cross-slope requirements.

The desires of the farmer must also be known in selecting the design standards for a specific job.   Minimum conservation- irrigation standards must be met. Oftentimes the farmer desires to have a still better job d that will save on labor and permit better farming practices .The engineer should attempt to design the best job the farmer is willing to accept and pay for. Usually the standards of the farmers go up from year to year, and a job that is perfectly satisfactory today may be considered substandard tomorrow. Many fields have been leveled and re-leveled several times; each time a field is leveled should be held to a minimum. Therefore, it is desirable to design to design as refined a job as the soil and farmer will permit.

It is generally accepted that the most desirable field surface for agricultural production is a plane surface on a nearly level grade. Like wise, the least desirable is one with such surface relief that irrigation can barely be accomplished and that unusually good management is required to obtain even fair irrigation water efficiencies.




Preparatory steps:

Land leveling is usually accomplished on a field- by- field basis. It is extremely important, there fore, to study the entire farm before attempting any leveling.
Land leveling is probably the most intensive practice that is applied to agricultural lands, and much expense can be saved by carefully dividing the farm into areas that have about the same slope and soil characteristics.
A topographic survey is always helpful and is usually necessary in planning a farm irrigation system. Such surveys may vary from a few scattered shots to a precise grid-type survey. Any of the conventional methods of making this survey are satisfactory, but it is important to locate and map benchmarks and points of known horizontal position in order to reestablish both vertical and horizontal control on the ground.

Prior to leveling design, the farm irrigation system must be planned so that the location of field boundaries, irrigation water supply system, drains, and field roads are known. The leveling plan for an individual field must provide for furnishing borrow to or for absorbing waste from these adjacent features. It must also provide for the proper ratio between excavation and embankment.
Before leveling, the field should be cleared of trash and vegetative material. In desert areas, sage and brush should be cleared, raked, and burned. On cultivated lands, mowing and raking or burning will usually suffice. Crop ridges should be eliminated by disking or smoothing . The grass on sod lands should be mowed and raked, but the vegetation should not be plowed under immediately prior to leveling. Any operation that leaves the surface in a loosened condition makes it difficult to grade to an exact elevation.