![]() Increase in drainage area increases both velocity and amount of runoff gathering in narred channel. ![]() Critical Length:Īnother approach in fixing the spacing of bunds by determining the critical length of land between adjacent bunds. The sum of these two should be minimum 4. Value of land lost permanently due to construction of bunds. The cost of Bunding includes two main atoms which vary according to the spacing of the bunds. The heights of waste weirs should be such that the bunds store just sufficient water to meet requirement of crop. For other crops, the capacity of the bund should be decided by the average consumptive use of the crop proposed and the maximum length of dry period in growing season. Therefore the bunds should be of such dimensions as to permit no runoff. Moisture Conservation:įor paddy lands it is desirable to store all the rain water for the use of the plants. Therefore the level of waste weir and the amount of land to be submerged should be decided by the cropping practice to be followed and the infiltration rate for the soil. The amount of land submerged due to pending and duration of pending will affect crops. The following factors are to be considered while developing design criteria for contour bunds. The height of bund should permit frees board of about 20% as design depth Specific at bund cross section are given in table The cross section area of of the storage space required can be calculated by the following formulaĬross section area of storage space = X / 100 In normal practice sufficient practice is provided to take care of runoff from rains expected in 10 year recurrence interval. The height of bund should provide sufficient storage above the bund to handle the expected runoff. The length of bund should be such that the velocity of water flowing between bunds should be non- erosive. The bund retains the runoff and carries it over the distance equal to bund length in one direction. In general, 400 to 500m is the maximum length of bund. Since the contour bunds are laid along the contours, they are level bunds. Table-1 Spacing of Contour bunds: Recommended by Gadkary Slope of land Spacing may be increased or decreased 10 to 20% to suit local conditions. I.īund spacing should not be so wide as to cause excessive soil erosion between adjacent bunds. Vertical distance is commonly known as the vertical interval or V. Although the horizontal spacing is useful in determining the row arrangement. Spacing of Contour bund:īund spacing is expressed as the vertical or the horizontal distance between corresponding points on two adjacent bunds. General principles & design of contour bund: 1. Contour bunds are also not successful in very shallow soils having a depth loss than 7.5cm. Further the poor drainage properties of deep black soils gives raise to long stagnation of water against contour bunds and make it unstable. It maintains soil fertility and increases water infiltration into the soil considerably,Ĭontour bunds in deep black soils have been a failure because of the nature of soil, which cracks during hot weather and cakes during the monsoon. Therefore under contour bunds an area of about 5 percent is lost under the bunds and is not available for cultivation.Ĭontour bunds can save soils from erosion to the extent of 25 to 162 tones/ hectare annually. No cultivation is allowed on the earthen embankments of contour bunds. They are not suitable in heavy rainfall areas. They serve as fences, and give protection from water and wind erosion in low rainfall areas. Peripheral bunds:īunds area also constructed along field boundaries without reference to contour. A series of such bunds divide the area into strips and act as barriers to t5he flow of water, thus reducing the amount and velocity of the runoff. It consists of building earthen embankments across the slope of the land, following the contour as closely as possible.
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