land levelling
TRANSCRIPT
On farm Development Activities & its Impact on Irrigation water Management.Land LevellingImportance of Land Levelling Land Levelling CriteriaLand levelling in relation to different methods of irrigation
On farm Development Activities
On farm techniques are focused on keeping water in the field, distributing it more efficiently, or achieving better soil moisture retention.
Examples The chiseling of extremely compacted soils Furrow diking to prevent runoff Land leveling for a more even water distribution Dry-land farming; and Land retirement.
The traditional gravity-fed system can be improved upon with the use of laser leveling or micro irrigation, though evaporation still leads to water loss.
Laser leveling involves grading and precisely leveling the soil to eliminate any variation in the gradient and reduce slope of the field.
Furrow diking is the practice of building small temporary dikes across furrows to conserve water for crop production, which may also aid in preventing erosion.
Farmers practicing dry-land farming in arid regions use a variety of techniques and land management practices to minimize water loss and erosion. These techniques include coordinating seeding to the ideal soil moisture content, choosing crops more suited for arid conditions, and fallowing.
Land retirement refers to a common policy of permanently or temporarily suspending farming on a particular acreage of land
Impact on Irrigation Water Management
• Practices such as chiseling, furrow diking, and land leveling allow the land to absorb water more efficiently and results in less waste.
• While chiseling, furrow diking, and land leveling help prevent runoff and allow the land to retain more water
• It allow the irrigator to monitor soil and water conditions to ensure water is delivered in the most efficient manner possible.
• This helps control the flow of the water and allows for more uniform soil saturation.
Land Leveling is reshaping of the field surface to a planned grade
To make a suitable field surface to control flow of water
To check soil erosion To provide for surface drainage.
Irrigated areas benefit greatly from land Leveling since the ground in its natural state is seldom suited for the efficient application of water
Land Leveling
In low rainfall areas, land leveling• Produces a smooth uniform land surface, • Reduces runoff and induces infiltration of rain
fall• Assures even moisture distribution.
On sloping ground, levelling eliminates small depressions, cuts and furrows which leads to concentration of runoff.
Proper land grading, coupled with surface drainage measures, reclaim unproductive poorly drained areas.
Criteria for land grading are influenced by
The characteristics of the soil profile, Prevailing land slope, Rainfall characteristics, Cropping pattern, Methods of irrigation, The preferences of the farmer.
Criteria of Land leveling
LAND CLEARING
Prior to making the land grading survey, it is advantageous to remove heavy vegetative growth from the land. Land clearing consists of removing some or all of the trees, bush, vegetation, trash and boulders and all roots.
A well-designed irrigation system delivers the required amount of water to all parts of the area to be irrigated at the required rate without damage to the soil or excessive loss of water.
The topography is a major factor in selecting The method of irrigation • Estimating the number and kind of water control
structures needed• Determining the need for land levelling • The relative elevations of the source and the
area to be irrigated• The drainage outlets
Phases of Land levelling operations 1. Rough grading2. Land levelling3. Land smoothing.
Land levelling design methods
1.Plane method2.Profile method 3.Plan inspection method4.Contour adjustment method
Plane method Procedure:
1.Determine the centroid of the field2.Determine the average elevation of
the field3.Compute the slope of the plane of
best fit4.Compute the formation levels, cuts
and fills5.Determine the cut-fill ratio
Mark grid points in the field
Survey the elevations and draw contour map
Determining the centroid of the field
The centroid of a rectangular field is located at the point of intersection of its diagonals. The centroid of a triangular field is located at the intersection of the lines drawn from its corners to the midpoints of the opposite sides.
To determine the centroid of irregular fields, the area is divided into rectangles and right-angled triangles. The centroid is located by computing moments about two reference lines at right angles to each other.
Determine the average elevation of the field
Adding the elevations of all grid points in the field and dividing the sum by the number of point give the average elevation.
Locate the centroid and fix its elevation as mean of the field
Compute the slope of the plane of best fit. The slope of any line in the x or y direction on the plane which fits the natural ground surface, can be determined by the least squares method.
nDD
nHDDHS
/}){()(
/)})({()(22
in whichS=slope of line in a p1ane, dimensionless*D= distance from the reference line, m H= elevation of the grid point, mn = number of grid points
Compute the formation levels, cuts and fills:
With the elevation of the centroid determined, the formation level of any point (the elevation which the point should attain after land grading operation) may be determined, using the computed or assumed values of Sx and Sy.
Mark the existing and computed elevation on grid points and compute cut/ fill
PROFILE METHOD
Essentially it consists of a trail and error method of adjusting grades on plotted profiles until the irrigation criteria are met with and the earthwork balance is attained.
PLAN INSPECTION METHODThe grid point elevations are noted on the plan, and the design grade elevations are determined by inspection after the careful study of the topography. It is largely a trial and error procedure.
In selecting the elevations formation level the designer must simultaneously consider the down field slope, cross slope, earth work balance and haul distance. The desired cut fill ratio and volumes of earthwork are estimated from the summation of cuts and fills.
The grades are frequently adjusted to obtain favourable earthwork balance and to maintain the down field and cross slopes within safe limits.
CONTOUR ADJUSTMENT METHODThe contour adjustment method of land levelling designs consists of trial and error adjustments of the contour lines on a plan map. The method is specially adapted to the smoothening of steep lands that have to be irrigated.
A contour map is drawn and the proposed ground surface is shown on the same map by drawing new contour lines. The uniformity of downfield slope is controlled by the uniformity of the horizontal spacing between contours, and the cross slopes can be examined by scaling the distance between contours at right angles to the direction of irrigation.
Importance of Land Leveling
• It permit uniform and efficient application of irrigation water.• The preparation of the field surface for conveyance and distribution
of irrigation water is as important to efficient surface irrigation as any other single management practice the farmer employs.
• to provide a slope which fits a water supply. • to level the field to its best condition with minimal earth movement
and then vary the water supply for the field condition. • Land leveling always improves the efficiency of water, labour and
energy resources utilization. • A field leveled to high standards is generally more easily irrigated
than one where undulations require special attention.
