2007 Ground Water Summit

Wednesday, May 2, 2007 : 1:00 p.m.

WAM and GAM: A Shotgun Wedding in Texas

Larry F. Land, P.E.1, David Dunn, P.E.1 and Barney N. Austin, PhD2, (1)HDR Engineering Inc., (2)Texas Water Development Board

WAM, a modeling system for estimating the amount of water available from a river or stream under a specified set of permits, projects, basin operations and hydrologic conditions, and GAM, a deterministic model for simulating groundwater flow within an aquifer that is in response to interactions with surface water features, such as reservoirs, streams, and springs, and a specified set of pumping and climate conditions, were requested to be wed (linked) by the some members in the water community. Major justifications for linking the models were more accurate tools for calculating the availability of surface water and groundwater and for estimating the impact of water development on streams and aquifers, and an assessment of impacts of groundwater development on environmental flows. As in most shotgun weddings, the relationship was based on an initial infatuation that impaired both parties’ vision and failed to recognize that the individuals were largely incompatible. In this case, WAM simulates the response of water rights (diversions and reservoirs) to a repeat of the hydrologic period of record, generally about 1940 through 1997; and GAM, on the other hand, simulates future aquifer conditions for an assumed pumping and recharge scenario.  Other issues were: lack of confidence in the accuracy of the results from the linked models by stakeholders, single WAM basins crossing multiple GAMs, and single GAMs crossing multiple WAMs, differences in geographic and temporal scales, representation and calculation of surface water-groundwater interaction, method of linkage (passive versus active), and data constraints. Consequently, the wedding (linkage) has been called off, for the time being, to allow both individuals (models) to mature and, hopefully, become more compatible.

Larry F. Land, P.E., HDR Engineering Inc. Mr. Larry F. Land, P.E. is a senior professional associate with HDR Engineering, Inc. in Austin, Texas and holds Agricultural Engineering degrees from Texas Tech University and Colorado State University. Mr. Land was with the U.S. Geological Survey-Water Resource Division for over 30 years and conducted many water resource studies. For the last 9 years, Mr. Land has been with HDR where he has conducted and managed water-resource projects for local and regional planning, development of municipal water supplies, water-well design, and conjunctive use of surface water and ground water.

David Dunn, P.E., HDR Engineering Inc. Mr. David D. Dunn, P.E., is a vice president with HDR Engineering, Inc. and holds degrees in Civil Engineering from the University of Nevada-Reno and from Texas A&M University. Mr. Dunn was one of the original developers of the Water Rights Analysis Package (WRAP) used by the Texas Commission on Environmental Quality, and has applied the model in multiple basins in Texas for various clients. His professional interests concentrate on water rights permitting and analysis, water supply planning and storm water systems.

Barney N. Austin, PhD, Texas Water Development Board Dr. Barney Austin is Director of the Surface Water Resources Division of the Texas Water Development Board (TWDB). He holds a BSc in Agricultural Engineering from McGill University in Canada and a PhD in Civil Engineering (Water Resources) from Salford University in England. After working several years for a government research institute and then an engineering consultancy firm, Dr. Austin now helps coordinate the water resources planning efforts for the state of Texas. Dr. Austin directs nine programs at the TWDB, including the Water Availability Monitoring and Instream Flow programs, for which understanding groundwater-surface water interactions is crucial.


The 2007 Ground Water Summit