SMIG -- Truckee-Carson Feature Article: March, 1996

Surface-water quality and flow Modeling Interest Group

The Truckee-Carson Program

by Larry Bohman

USGS, Water Resources Division
333 West Nye Lane, Room 203
Carson City, NV 89706
Internet: lrbohman@usgs.gov
Phone: (702) 887-7679
FAX: (702) 887-7629

Editor's note:
Larry's group has just published a couple of USGS Fact Sheets on their modeling efforts in the Truckee-Carson. They have been digitized and are available here:

Fact Sheet FS-165-95: Interactive Computer Program to Simulate and Analyze Streamflow, Truckee and Carson River Basins, Nevada and California
by Larry R. Bohman, Steven N. Berris, and Glen W. Hess
Fact Sheet FS-082-96: Simulation of Selected Reservoir Operations in the Upper Truckee River Basin, California
by Steven N. Berris, Glen W. Hess, and Kenn D. Cartier

After decades of litigation and negotiation, the Truckee-Carson-Pyramid Lake Water Rights Settlement Act, Public Law 101-618, was passed by Congress in 1990. The law provides a framewoork for constructing a complex combination of operating criteria to balance interstate allocation of water and water demands for municipal, irrigation, fish and wildlife, water-quality, and recreational uses in the Truckee and Carson River Basins of Nevada and California.

The USGS Truckee-Carson program was established to support the Department of the Interior in the implementation of the law as follows:

Consolidate and (or) develop as necessary a streamflow and water-quality gaging-station network in order to document water resources and support river operations.
Calibrate, test, and use interbasin hydrologic and hydraulic computer models to support the management and allocation of water and the assessment of environmental effects.
Provide technical guidance to other Federal agencies during negotiations for the Truckee River Operating Agreement.

Most of the models being used are based on the watershed model HSPF (Hydrological System Program -- FORTRAN). This is a well-documented set of public-domain programs capable of continuous simulations of water quantity and quality at hourly, daily, monthly, or annual timescales. To date, flow-routing models of the two mainstem channels, all major lakes and reservoirs, and the Truckee Canal (which provides for the interbasin transfer of water) have been constructed and the documentation is currently in review. Models simulating stream temperature and total dissolved solids within the Truckee River are also near completion. Another computer model developed within the Survey, the Precipitation-Runoff Modeling System (PRMS), was chosen to simulate flow inputs from the alpine watersheds to the stream channel and reservoir systems of both basins. A single model was recently (1992) developed for the entire Carson River Basin under the Climate change Program. However, pervasive regulation prohibits the development of a similar single river basin-scale catchment model of the Truckee River Basin, thus requiring the disaggregation of the basin into sub-basin and reservoir-catchment models. Also, due to time constraints and the existence of large ungaged areas of the Lake Tahoe and upper Truckee River Basins, it will be necessary to devise a technique for regionalizing model input parameters. This task will be facilitated through the use of digital data (altitude, slope, aspect, land cover, soils, and geology) within a geographical information system.

In order for the modeling system to be an effective management and policy-analysis tool, the physical models described above must be linked to models simulating operations/allocations and there must be a "friendly" basic user interface for analysis of alternative management scenarios. To address the first issue, Alan Lumb (HASS, Reston) in conjunction with Aqua Terra Consultants has modified HSPF to allow conditional logic for simulating reservoir operations and river diversions. No compilation of operations and allocations currently exists for the two basins and development of this operational simulation capability within HSPF, as with most new software, is time-consuming. Learning and translating system operations into code will consume most of the project funding over the next few years.

Easy-to-evaluate numerical, statistical, and graphical results are needed to allow managers to test and improve long-term operating policies responsive to the many competing demands for water. GENSCN (GENeration adn analysis of model simulation SCeNarios) is an interactive computer program, also developed by HASS and Aqua Terra in part with TCP funding, that represents the first step toward the development of such a basic user interface. GENSCN is designed to create and run different model scenarios. The user may then examine the results of a single model run or compare the results of two or more runs by choosing any combination of constituent, location, and scenario and selecting the appropriate tabular, graphical, or statistical option from a menu. In addition to these basic functions, GENSCN can also track water ownership as it flows downstream. Through animation, GENSCN can also aid the user in seeing where, when, and how long critical thresholds are exceeded for any modeled constituent at any reach boundary along the river.

Although development and calibration of these models is basin-specific, the underlying decision-support modeling system has national transfer value.

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U.S. Geological Survey
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