IWFM / IDC

IWFM (Integrated Water Flow Model) / IDC (IWFM Demand Calculator)

Criterion	Explanation
General Description	IWFM (Integrated Water Flow Model) is a model for water resources management and planning. It simulates surface and groundwater movements and uses due to agricultural and municipal/industrial sources. IDC (IWFM Demand Calculator) is a standalone module that can be used to calculate the water demand by itself.
Model Domain	The model domain consists of a user-specified model area, including land surface, surface water streams, and unsaturated/saturated zones under the land surface.
Developer	CA Department of Water Resources (DWR)
Hardware computing requirements	None given
Code language	FORTRAN
Original application	Simulation of surface and groundwater flow, soil moisture, and consumptive water use
Public/proprietary and cost	Distributed under the GNU General Public License v3.0; Free of charge
Physically or empirically based	Physically based
Mathematical methods used	Groundwater flow in the saturated zone is a numerical solution of the Richards' equation via the Galerkin finite element method. Surface flow routing to streams is pre-specified by the user with flow rates based on a Soil Conservation Service (SCS) curve number (CN) approach. Surface flow routing between stream nodes takes a mass balance approach with surface levels determined by a user-specified curve number. Evaporation for each land use type is user-specified as a time series input.
Input data requirements	Input data consists of aquifer stratigraphy, land-use information, surface water flow boundary conditions, precipitation and ET boundary conditions. The ease of assembling this information depends on the specific model domain and application.
Outputs	Spatial and temporal detail is model-dependent. Surface and groundwater budget data is saved in a proprietary binary format. The model includes post-processing programs to extract desired features into whitespace-separated text files.
Pre-processing and post-processing tools	IDC is a standalone component for the water demands in IWFM. There is a IWFM mesh generator plugin for ArcMap to generate finite-element meshes. A plugin for Microsoft Excel is available to help import model output and format time series data. Soil builder tools, either with or without ArcMap integration, exist to process NRCS SSURGO soil database information about the root zone into IWFM's input file formats. IWFM PEST utilities aid automatic calibration of model parameters. A land use adjustment preprocessor is available to generate time series data for land uses.
Representation of uncertainty	Not explicitly represented in output; could be implemented via multiple scenarios
Prevalence	Best-known application is CA DWR's C2VSIM, a model of California's Central Valley surface and groundwater use. IWFM has also been used for modeling local domains by other agencies in California.
Ease of use for public entities	Model documentation is detailed and understandable. Largest barrier to entry for a novel application would likely be quality data on aquifer stratigraphy and land-use.
Ease of obtaining information and availability of technical support	There is an IWFM users group, and the model developers are able to respond to well-formulated questions.
Source code availability	Yes, publicly available on the model website
Status of model development	The model is mature but continues to receive new features and improvements (latest release April 2018).
Challenges in integration	Because the model is open source, well documented, and has an active user and development community, challenges to integration are few.