Depth-Area-Storage Capacity Relationships of Village Tanks

Village Tanks in Sri Lanka have the potential to enhance climate resilience particularly through water management. The depth-area-capacity curves are very important for their improved management. However, many of these small reservoirs do not have such curves and it is difficult to develop them due to the reservoirs being numerous. Attempts to fit an equation to these curves have been carried out for a long time. This work analysed the data from approximately 150 Village Tanks, tested the validity of the equations currently used in Sri Lanka, and attempted to improve the presentation of depth-area-capacity relationships through modification to existing equations. The results show that a frequently used older equation is still valid with slight modifications. When the absolute values of the variables used in that equation are replaced by relative values, a linear relationship with a high correlation coefficient and small variation of the gradients of the linear plots was obtained. It was also found that a substantially accurate depth-area-capacity relationship could be derived with 4 to 5 measurements of depth and water surface area. The use of relative variables has several advantages including the ability to readily indicate the status of water availability in the Tank.