Data View, Branch: Supply
and Resources \ Groundwater, Category: Physical, Tabs: Method, Hydraulic
Conductivity, Specific Yield, Horizontal Distance, Wetted Depth, Storage
at River Level 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. Groundwater levels respond to natural recharge from precipitation, but can also be influenced by irrigation in the watershed, where a portion of this water may recharge the aquifer rather than be taken up by the target crop.
To simulate groundwater interactions with surface waters, there are four options.
Specify directly the amount of groundwater inflow to a particular river or reach
Have WEAP model these interactions (groundwater "wedge" connected to river)
Have WEAP model these interactions (deep soil layer of Soil Moisture method catchment)
To select option 1 or option 2, go to particular groundwater node in the Data view under the Groundwater branch of Supply and Resources, and click on the Method tab. For option 3, create one or more catchment nodes with infiltration links to the groundwater node and enter data for the deep soil layer. If you are linking WEAP to MODFLOW, you should leave all surface water-groundwater interaction variables blank.
If you choose to specify the amount of groundwater inflow from or outflow to a river or reach (option 1), the values can input under the "Groundwater Inflow" and "Groundwater Outflow" tabs in the Inflows and Ouflows section for that river or reach.
WEAP can also model groundwater-surface water interactions using a stylized representation of the system (option 2). Groundwater can be represented as a wedge that is symmetrical about the surface water body, such as a river; recharge and extraction from one side of the wedge will therefore represent half the total rate. The recharge or extraction volumes are dependent on the elevation between the groundwater table (the surface representing full saturation of aquifer pore spaces) relative to the wetted depth of the river (see definition below). The additional parameters required to use this method are:
Wetted Depth: the depth of the river. This value is used as the reference for comparison to the simulated groundwater elevation.
Storage at River Level: the groundwater storage volume at which the top of groundwater is level with the river.
Specific Yield: the porosity of the aquifer, represented as a fractional volume (a number greater than 0 and less than or equal to 1) of the aquifer.
Hydraulic Conductivity: a measure of the ability of the aquifer to transmit water through its pores, represented in units of length/time.
Horizontal Distance: a representative distance for the groundwater-river geometry, taken as the length from the farthest edge of the aquifer to the river.
In addition to these aquifer-specific parameters, you will need to enter the Reach Length--the horizontal length of the interface between the reach and linked groundwater--as data for each reach that is connected to the aquifer.
Entered on: Data View, Branch: Supply
and Resources \ Groundwater, Category: Physical, Tabs: Method, Hydraulic
Conductivity, Specific Yield, Horizontal Distance, Wetted Depth, Storage
at River Level