Local Reservoir Flows

Local reservoirs are identical to river reservoirs, except that they are not located along a river, tributary or diversion and therefore do not have inflow from these sources. All other properties of the local reservoir calculations are the same as river reservoirs. In detail, a local reservoir's (Res) storage in the first month (m) of the simulation is specified as data (see Supply and Resources\Local Reservoirs\Storage).

BeginMonthStorageRes,m = InitialStorageRes for m = 1

Thereafter, it begins each month with the storage from the end of the previous month.

BeginMonthStorageRes,m = EndMonthStorageRes,m-1 for m > 1

This beginning storage level is adjusted for evaporation. Since the evaporation rate is specified as a change in elevation (see Supply and Resources\Local Reservoirs\Physical\Net Evaporation), the storage level must be converted from a volume to an elevation. This is done using the volume-elevation curve (specified as data--see Supply and Resources\Local Reservoirs\Physical\Volume Elevation Curve).

BeginMonthElevationRes = VolumeToElevation( BeginMonthStorageRes )

The elevation is reduced by the evaporation rate.

AdjustedBeginMonthElevationRes = BeginMonthElevationRes - EvaporationRateRes

Then the adjusted elevation is converted back to a volume.

AdjustedBeginMonthStorageRes = ElevationToVolume( AdjustedBeginMonthElevationRes )

A reservoir's operating rules determine how much water is available in a given month for release, to satisfy demand and hydropower requirements and for flood control. These rules operate on the available resource for the month. This "storage level for operation" is the adjusted amount at the beginning of the month, plus demand site (DS) and treatment plant (TP) return flows that come in at that point.

StorageForOperationRes = AdjustedBeginMonthStorageRes + DSReturnFlowDS,Res + TPReturnFlowTP,Res

The amount available to be released from the reservoir is the full amount in the conservation and flood control zones and a fraction (the buffer coefficient fraction is entered as data--see Supply and Resources\Local Reservoirs\Operation) of the amount in the buffer zone. Each of these zones is given in terms of volume (i.e. not elevation). The water in the inactive zone is not available for release.

StorageAvailableForReleaseRes = FloodControlAndConservationZoneStorageRes + BufferCoefficientRes x BufferZoneStorageRes

All of the water in the flood control and conservation zones is available for release, and equals the amount above Top Of Buffer (TOB and other reservoir zones levels are entered as data--see Supply and Resources\Local Reservoirs\Operation),

FloodControlAndConservationZoneStorageRes = StorageForOperationRes - TopOfBufferZoneRes

or zero if the level is below Top Of Buffer.

FloodControlAndConservationZoneStorageRes = 0

Buffer zone storage equals the total volume of the buffer zone if the level is above Top Of Buffer,

BufferZoneStorageRes = TopOfBufferZoneRes - TopOfInactiveZoneRes

or the amount above Top Of Inactive if the level is below Top of Buffer,

BufferZoneStorageRes = StorageForOperationRes - TopOfInactiveZoneRes

or zero if the level is below Top Of Inactive.

BufferZoneStorageRes = 0

WEAP will release only as much of the storage available for release as is needed to satisfy demand and hydropower requirements, in the context of releases from other reservoirs and withdrawals from rivers and other sources.  Note: because a local reservoir is not on a river, any water released to satisfy a hydropower energy demand will disappear from the system.

OutflowRes = TransLinkInflowRes,DS + ExtraOutflowForHydropowerRequirement

where

OutflowRes StorageAvailableForReleaseRes

The storage at the end of the month is the storage for operation minus the outflow.

EndMonthStorageRes = StorageForOperationRes - OutflowRes

The change in storage is the difference between the storage at the beginning and the end of the month. This is an increase if the ending storage is larger than the beginning, a decrease if the reverse is true.

IncreaseInStorageRes = EndMonthStorageRes - BeginMonthStorageRes