What is it?
Groundwater recharge is defined as the entry of water from the unsaturated zone into the saturated zone at the water-table surface (Freeze and Cherry, 1979).In IGW-NET, water may be added as an input to the aquifer through the top boundary as recharge (precipitation/surface water that infiltrates down to the water table).
How to use it:
Recharge to the aquifer is treated as specified flux [L/T] that is constant in time. (Time-varying recharge can be assigned using Zone features). Users can:(1) specify a single value to be applied through the model domain (default setting)
(2) use a spatially-variable recharge raster available from the MAGNET4WATER Data Center
(3) use their own raster file (check the box next to the ‘Import’ link, select the link to open a file browser, and browse to and select the appropriate file for importing)
(4) use a WCS (raster) data layer from DataNET
(5) assign recharge from M4W surface water model (output from watershed modeling) - SwaNET or USGS INFIL (module within IGW-NET).
Note that zones may be added to the model to assign a recharge value that overrides the value(s) provided in the Default Parameters and Options menu.
MAGNET4WATER Data Center Layers
Multiple data layers representing long-term average recharge area available from the MAGNET4WATER server. Most layers are geographically limited. An option with global coverage is available, but the quality/resolution of the recharge layer depends on location.NOTE: when an option is selected, click the '?' button next to the drop-down menu to preview the layer abstract and display the layer in the map display.
Also, a number of WCS web data service layers representing recharge (including those listed here) are available on DataNET for transfer into IGW-NET (see below).
1. Global w/MI Patch
The default layer is global in extent. For most of the world, recharge estimates are from a relatively crude, 1 degree by 1 degree (~111 km by 111 km) raster layer described in Pokhrel et al. (2015): "Incorporation of groundwater pumping in a global Land Surface Model with the representation of human impacts". Water Resources Research, 51(1), pp.78-96.For the State of Michigan, a high-quality "patch" or different recharge raster layer is used (1609 m resolution), generated following empirical methods presented in Holtschlag (1997) involving observed stream flow hydrographs and information related to land use, soil conditions, and watershed characteristics.
Holtschlag, D.J. (1997). A generalized estimate of ground-water-recharge rates in the Lower Peninsula of Michigan (No. 2437). US Geological Survey; Information Services [distributor],.
2. USA Long-term Mean
Dataset of long-term average estimates of recharge rates over the time period 2000-2013, for contiguous US (spatial resolution: 800m). From Reitz et al. (2017): "Annual estimates of recharge, quick-flow runoff, and ET for the contiguous US using empirical regression equations, 2000-2013: U.S. Geological Survey data release, https://doi.org/10.5066/F7PN93P0.3. Global Precip.
Mean global precipitation (spatial resolution: ~11.1km), from NASA's Integrated Multi-satellitE Retrievals for GPM (IMERG) program. See https://gpm.nasa.gov/data/imergNOTE: When using this layer, consider applying a fractional multiplier to account for the fact that recharge (net infiltration) is only a portion of the rainfall (say, for example, 1/3 or precipitation becomes recharge).
To apply a multiplier, check the box next to 'Recharge' under 'Multuplying Factor' section in Domain Attributes menu, and enter a value between 0.0 and 1.0.
4. Europe/Africa
This option applies to one of two layers, depending on the location of the site being modeled.If modeling in the European domain, recharge rate estimates come from the European Geological Data Infrastructure (EGDI) and were originally generated in the TACTIC project. Estimates are for the 1981-2010. The gridded dataset has a spatial resolution of 1km.
If modeling in Africa, recharge rates are estimated from the dataset prepared by MacDonald et al. (2020): "Groundwater recharge in Africa from ground-based measurements". British Geological Survey. Estimates are for the 1970-2020. The gridded dataset has a spatial resolution of 31km.
User-provided Raster
The following raster file formats are supported for import of user recharge data layers:1 - Ascii format with the same projection (PRJ) as your model PRJ
2 - Geotiff (.tif) format with PRJ information embedded in the .tif file
3 - IMG format with PRJ information embedded in the .tif file
DataNET WCS layer
This option allows users to import from MAGNET4WATER DataNET a WCS data layer as a raster file of aquifer recharge. A "linked" DataNET page needs to be opened to be able to send a WCS layer from DataNET into AquaNET (a prompt will appear if that is the case, allowing the user to open a new DataNET page to be linked).Once the WCS layer is transferred into AquaNET, it will be converted into a geotiff raster file uploaded to your user folder.
See the 'DataNET-based Model' Quick Tutorial for an example.
From SW Model Output
Select this option to utilize the recharge output from a previously executed SwaNET model. (Saving the recharge output to your M4W user folder is initiated within SwaNET --> Save/Publish SWAT Model’ menu).Once selected, click 'Use Uploaded File' and select:
- 'SWATMeanRech.T' or 'InfilMeanRecharge' for steady state (long-term average) from SwaNET or IGW-NET's INFIL recharge module, respectively); or
'SWATRech.T' or 'InfilRecharge' for the transient recharge outputs.