Land Atmosphere Water Simulator (LAWS) Version 2.0
The Land Atmosphere Water Simulator (LAWS) Version 1.0 (completed in December 2004) is a fully integrated, flexible, and scalable tool that allows users to rapidly perform and analyze simulations of alternative land, vegetation, infrastructure, and water management strategies using either historic or forecasted meteorology.
Several important features affecting agricultural water use were not included in Version 1. For LAWS Version 2.0, these limitations will be addressed by adding new capabilities to simulate water table elevation, stream-aquifer interactions, and the effects of irrigation on drainage and river water quality.
Other important modifications to LAWS will include changes to the evapo-transpiration (ET) algorithm for simulating the effects of soil water salinity and low water content on actual crop ET rates.
Need and Benefit
LAWS differs in several significant ways from existing water resource planning and operations models currently available to Reclamation managers, planners, and operators.
First, LAWS simulates daily, field-scale land, crop, and water management practices. It provides users with tools to simulate alternative methods for managing soil moisture on a daily basis during the irrigation season based on soil properties, crop type and growth stage. This approach permits LAWS to compute ET, soil water content, surface water ponding, runoff, canal and drain losses, return flows to rivers, and deep percolation to ground water at a level of spatial and temporal resolution not present in existing planning and operations models. Although LAWS performs these calculations at the field scale, LAWS also provides users with ability to aggregate these results within larger user definable areas so that water budgets can be readily computed for arbitrary organizational regions.
Second, LAWS is not an optimization model. Although LAWS provides users with multiple methods for allocating water supplies and making priority based delivery decisions, LAWS does not employ any mathematical methods to determine what is the "best" allocation of water. In contrast, LAWS provides users with a powerful graphical user interface (GUI) that allows users to readily change water allocation and delivery priorities, land and crop management practices, and infrastructure characteristics to compare the effects of alternative system configurations on reservoir water supplies.
Third, LAWS has a native Geographic Information System (GIS) capability built directly into the GUI. This GIS capability allows users to set up and analyze spatially accurate LAWS simulations across a span of scales--ranging from large regional watersheds to sub-regions contained with individual fields. LAWS also provides users with the capability to import imagery, maps, and GIS information developed with commercially available software packages. Furthermore, LAWS has been developed from the U.S. Army Corp of Engineers (Corps) Water Management System (CWMS) software from which it has inherited a powerful suite of tools to examine model outputs including side by side comparisons of outputs from multiple alternative simulations and animations of spatial and temporal time series results.
The LAWS enhancements proposed in this project will continue to build on LAWS unique capabilities. The development of a ground water simulation capability will permit user to evaluate the effects of both deep percolation and ground water pumping on water table elevations. This important feature will permit LAWS to be used as a planning tool in the evaluation of ground water-surface water conjunctive use management projects. It will also allow the LAWS user to evaluate the affect of high water table conditions on root zone water content and soil water salinity.
The development of a water quality simulation capability will give the user the capability to assess the effects of root zone salinization on deep percolation and drain water. The water quality simulation capability will also provide the user with the tools to assess the effects of drain discharge into explicitly simulated receiving waters.
The proposed modifications to ET algorithm will improve LAWS ability to simulate the reduction in actual ET as soil water content decreases. The effects of high soil water salinity on ET will also be added to the model.
The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.
Land Atmosphere Water Simulator Version 2.0 (final, PDF,
By Dr. Michael Tansey, Dr. Charles Young, Shannon Larson and John DeGeorge
Manual completed on August 03, 2011