The total water supply available for irrigation is the sum of natural flow, storage and return flow less residual storage and flow passing Sunnyside dam. Only proratable users will receive a proratable supply. Prorationing is currently not in effect, since the system is not on storage control. However given this range of potential prorationing, irrigation districts and water users are urged to apply their own judgement in deciding which level of supply may be realized. Water demands requiring storage releases, even prior to storage control, may be charged to the users total entitlement.
Subsequent precipitation is only one factor affecting the amount of water supply finally available.
This can tend to improve the proration level that is ultimately adopted. If warm, drier weather prompts an early run-off, the situation could worsen. On or near the beginning of storage control, the Bureau of Reclamation will announce the formal levels of pro-rationing. Normal capacity is 157,800 acre-feet.