Inflows and Outflows

In many watersheds, surface waters and groundwater are hydraulically connected. A stream can contribute to groundwater recharge (a "losing" stream) or can gain water from the aquifer (a "gaining" stream) depending on the level of groundwater in the aquifer. These flows between surface water and groundwater can be handled in WEAP in one of two ways.

Either

  you can specify directly how much flows from surface to groundwater (Groundwater Outflow) and from groundwater to surface water (Groundwater Inflow),

or

  WEAP can model these flows based on the level of the groundwater table and the Reach Length. For more information, see Groundwater-Surface Water Interactions.

In addition to flows to and from groundwater, flow on river reaches can be reduced by Evaporation and increased by Surface Water Inflow.

Both evaporation losses and groundwater outflow are specified as percentages of streamflow, while surface water inflow and groundwater inflow are entered as volumes.

Surface water inflow represents either non-point runoff into the river, or the confluence of streams or rivers not otherwise modeled. You may specify this inflow using the Water Year Method, the Read from File Method, or with an expression. See Specifying Inflow for details.

For groundwater interactions, you must specify to which Groundwater Source each reach is connected.

If a reach is connected to a groundwater node for which you've chosen to model the flows based on the level of the water table, then you will need to enter the Reach Length--the horizontal length of the interface between the reach and linked groundwater.

Entered on: Data View, Branch: Supply and Resources \ River \ <River Name> \ Reaches, Category: Inflows, Tabs: Surface Water Inflow, Groundwater Inflow, Groundwater Outflow, Evaporation, Reach Length.