The watershed model solver allows for simulating land surface hydrology (near-surface water balance) and calculating daily net infiltration or groundwater recharge, accounting for precipitation, evaporation/evapotranspiration, land surface runoff, and surface water inflows/outflows.
The watershed solver utilizes INFIL 3.0 — a grid-based, distributed-parameter, semi-empirical/semi-process-based watershed model used to estimate net infiltration below the root zone (USGS 2008). Drainage basin characteristics and daily climate records of precipitation and air temperature are used to estimate the daily near-surface water balance.
A. Turn On Watershed Module
B. Coupling/Decoupling to/from Groundwater
C. Channel/Stream
D. More/Less (Additional Options)
E. SW Infiltration as GW Recharge
F. Overland Flow Solver, Run-on Option
G. Rainfall Duration
H. SW Routing Options
A. Turn On Watershed Module
To activate the IGW-NET watershed module, set the solver parameters here, and enable "Overland Flow" in at least one model zone (Zone Attributes editor > Flow properties > Overland Flow...). To apply the watershed module across the entire model domain, use a zone that is the same size/extent as the model domain: Conceptual Model Tools > Zones > Zone=DM ... then turn on 'Overland Flow'.B. Coupling/Decoupling to/from Groundwater
Net infiltration output from the watershed module can be used directly as groundwater flow model input (i.e., coupled recharge-groundwater flow modeling, where computed recharge is applied at each time-step of the groundwater flow model).By default, groundwater flow modeling is not active during watershed model simulation (the modules are "decoupled"). Check the box next to 'SW Infiltration as GW Recharge' to couple the recharge-groundwater modules.
C. Channel/Stream
Check the box and change the solver settings to apply model stream/channel interactions. Channel networks can be loaded into the model from saved files by clicking "Load Channel Properties and Links from File".Number of SW sub-time steps (integer) - time discretization for the surface water model, or how many surface water time steps in each groundwater time step.
Note that the minimum time-step for INFIL 3.0 is one day.
D. More/Less (Additional Options)
Save Transient Rch - check the box and select start and end dates to save transient recharge values (default: unchecked).Saving the recharge files allows them to be used as spatially-variable (raster map) input to a IGW-NET groundwater flow model, either as transient (e.g., daily) input for unsteady flow modeling, or as a long-term mean for steady flow modeling.
Users can save transient recharge at each time-step, or just the mean annual recharge (spatial distributions).
Coming soon: saved transient recharge files can be downloaded to local machines for additional analysis or use in other hydrologic models.
Annual Mean - check the box and select start and end dates to save spatial distribution of the annual monthly mean recharge values (e.g., mean January recharge values across all years of simulation, the mean February recharge value across all years of simulation, and so on).
In all cases (box checked or unchecked) annual mean recharge and annual monthly mean recharge (Rch), precipitation (Precip), and evapotranspiration (EVT) are output at 6 "typical" locations within the model domain (one location in each quadrant, and two near the middle).
E. SW Infiltration as GW Recharge
Check the box to apply surface water infiltration to the groundwater model as recharge (default: unchecked).Save Soil Storage - to save soil storage check the box and upload/choose initial soil storage file *.T and *.V (default unchecked).
F. Overland Flow Solver, Run-on Option
At this time, only non-process based (INFIL 3.0) watershed flow solver is available.Check the "run-on" box to simulate run-on in addition to runoff. (This allows for surface-water runoff from and run-on to adjacent grid cells to simulate the daily water balance for each cell, meaning not all runoff becomes streamflow which can be particularly important in areas with varied soil types and topography).
G. Rainfall Duration
Select the duration and intensity for seasonal rainfall to be used in the model. For each season pick the number of hours of rainfall per day, and the start and end dates of the season. (defaults: summer 2 hr/day June-Aug, fall 12 hr/day from Sept-Nov, winter 12 hr/day from Dec-Feb, and spring 12 hr/day from Mar-May)H. SW Routing Options
Surface water routing across the model can be specified based on channel type/size by checking the box and specifying values.Use Routing Options - choose whether SW is routed (default unchecked).
Chn1 to Chn4 - (defaults: 0.001, 300, 0.08, 0.002)
MaxIter - the number of iterations to use when solving SW routes (default 10)
KsChn1 to KsChn3 - (defaults: 100, 2000, unchecked, 0.002). KsChn3 is optional and can be applied by checking the adjacent box.
After editing parameters and data click "save" to apply the settings to the model.