Documentation for a digital computer model of nutrient and dissolved-oxygen transport in the Truckee River and Truckee Canal downstream for Reno, Nevada

Abstract

A digital water-quality model was constructed as part of a waterquality assessment of the Truckee River downstream from Reno. This report provides documentation on the computer code and the principal data sets used in model calibration, validation, and simulations. The TRWQ Model simulates mean daily concentrations of constituents at specified increments along the length of the modeled river reach. Simulated parameters include: Conservative variables (mass balance of all inputs and losses): Water discharge Dissolved solids Specific conductance (used as an easily-measured surrogate of dissolved solids) Nonconservative variables (mass balance of all inputs and losses coupled with first-order transformation and decay algorithms): Ultimate carbonaceous biochemical oxygen-demand (CBODu) Organic nitrogen Ammonia nitrogen Nitrite nitrogen Nitrate nitrogen Orthophosphorus (two values, see Appendix II) Total phosphorus Ratio of inorganic nitrogen to orthophosphorus Reaeration rate Dissolved oxygen EXAMPLE DATA SETS Listings of example data sets used as the basis for published TRWQ Model simulations are presented in Appendix II. These eight data sets include final calibrated and validated model parameters and input data reflecting conditions observed in the Truckee River and Truckee Canal during extensive field investigations in

Phosphorus in the Truckee River between Vista and Patrick, Storey and Washoe counties, Nevada, August 1984

“…Regardless of the lack of laboratory determinations of TP for Lockwood and Patrick, apparently the fairly large increase in concentration (about 0.3 mg/L TP) observed at Patrick (table 5) is an artifact of sampling and time-of-travel idiosyncrasies. For example, because the estimated traveltime between Lockwood and Patrick was 6.6 hours [this value was used in the TRWQ model (Nowlin, 1987)], the six highest concentrations at Patrick on August 8,1979 (0.97,1.1, 1.3,1.3,0.96, and0.80 mg/L: La Camera andothers, 1985, p. 48), probably represented the phosphorus that had passed through Lockwood before the first water sample had been collected there, at 1:00 p.m. (1300 hours).…”

“…The same basic rationale described in the foregoing paragraph can be applied to this data set with regard to the two initial high values (0.95 and 0.77 mg/L TP) that outlie the rest of the TP data set for Patrick on August 13 (La Camera and others, 1985, p. 48). Subtracting a traveltime of 6.3 hours [the estimate used in the TRWQ model (Nowlin, 1987)] from the individual samplecollection times at Patrick would place a flow parcel at Lockwood before the sampling crew even arrived. Ignoring the two uncharacteristically high TP values for Patrick and the anomalously low 0.18 mg/L from the Lockwood data set (La Camera and others, 1985, p. 45), would result in an arithmetic mean value of 0.48 mg/L TP at both stations.…”

“…Recent analysis of available water-quality data from the river downstream from Reno showed that inputs or accretions of phosphorus to the river between Lockwood and Patrick appeared to be important. The significance of these undocumented loadings came to light during the calibration of the U.S. Geological Survey's Truckee River Water-Quality model (Nowlin, 1987). For example, calibration of the numerical model to observed Geological Survey synoptic data for August 1979and August 1980(La Camera and others, 1985 showed that nonpoint loads of about 540 Ib/d and 360 Ib/d would be required in the reach between Lockwood and Patrick, respectively, to duplicate measured instream concentrations.…”

Reaeration-rate coefficients for two reaches on the Truckee River downstream from Reno, Nevada, 1999

“…The Truckee River, located in eastern California and western Nevada, is facing increased stress due to continued growth in the Reno and Sparks urban areas. Studies by Nowlin (1987) and Caupp and others (1997) as well as current efforts are being used to understand the dynamic processes that control the quality of water in the river. Models are currently being developed that will give regulatory agencies the necessary information to better manage the river and enhance water quality, especially downstream from the Truckee Meadows (Caupp and others, 1997).…”

“…Allowable discharges from waste-water treatment facilities that will not adversely affect the water quality of a stream are calculated using the reaeration-rate coefficient (Melching and Flores, 1999). Nowlin (1987) reported calculated reaeration-rate coefficients for the Truckee River, downstream from Reno and Sparks, ranging from 2.52 to 17.1 per day for streamflow ranging from 47 to 380 ft/s, respectively. These reaeration-rate coefficients were calculated using measurements made with the gas-tracer method, with ethylene as the tracer gas.…”