The demand should be compared with supplies available year by year. If the demand is limited and less than the available run-off, storage may be fixed to cater to that  particular demand which is in excess of the run-off. The rough and ready method is the mass curve method for initial sizing. 

Even while doing the above exercise, water use data are needed to assess the impact of human activities on the natural hydrological cycle. Sufficient water use information would assist in implementing water supply projects, namely, evaluating the  effectiveness of options for demand management and in resolving problems inherent in competing uses of water, shortages caused by excessive withdrawal, etc. Water demands existing prior to construction of a water resource project should be considered in the design of project as failure to do so may result in losses apart from legal and social problems at the operation stage. 

Committed and Future Upstream Uses 

The reservoir to be planned should serve not only the present day requirements but  also the anticipated future needs. The social, economic and technological developments may bring in considerable difference in the future needs/growth rate as compared to the present day need/growth rate. Committed and upstream future uses should also be assessed in the same perspective. 

Criteria for Assessing The Success of The Project 

Water Resources Projects are to be designed for achieving specified success. Irrigation projects are to be successful for 75 percent period of simulation. Likewise  power projects and water supply projects are to be successful for 90 percent and nearly 100 percent period of simulation respectively. 

Density Current Aspects and Location of Outlets 

Density current is defined as the gravitational flow of one fluid under another having slightly different density. The water stored in reservoir is generally free from silt but the inflow during floods is generally muddy. There are, thus two layers having different densities resulting in the formation of density currents. The density currents separate the water from the clearer water and make the turbid water flow along the river bottom. The reservoir silting rate can be reduced by venting the density currents by properly locating and operating the outlets and sluice ways.