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Environmental Applications and Research Group — Publications

Water Supply and Water Quality in Totten Reservoir, Montezuma County, Colorado

Technical Memorandum No. 8220-98-09
Chris Holdren and S. Mark Nelson

Hydrologic Budget
Lake and Stream Water Quality
Effects of Total Dissolved Solids on Fisheries


Totten Reservoir was built in 1965 to store water from the Dolores River for irrigation purposes. The current project was initiated to determine the quality and quantity of water available to sustain the existing fishery in Totten Reservoir. Available information on water quality and water supply in Totten Reservoir was used to evaluate proposed changes in area water allocations.

Totten Reservoir is currently owned by the Montezuma Valley Irrigation Company (MVIC), although it has not been used for irrigation in recent years. From 1965 to 1986-87, the reservoir was filled with runoff in the spring, with 40 to 45 cubic feet per second (cfs) of Dolores River water being passed through Totten Reservoir from approximately mid-April to mid-July (approximately 5,900 to 6,700 acre-ft/yr). Water was then withdrawn from Totten Reservoir at a rate of about 10 cfs from July to October for irrigation purposes (approximately 1,800 acre-ft/yr). Following the completion of McPhee Reservoir in 1986-87, water was diverted from that reservoir through the Dolores Tunnel and Rocky Ford Ditch to Totten Reservoir following the same schedule as the earlier Dolores River diversions.

Totten Reservoir was taken off-line following completion of the Towoac/Highline Canal in 1992 and is no longer a major part of the regional irrigation system. Since that time, tail- water releases from the Goodland Ditch, return flows and as-requested diversions from McPhee Reservoir have been the major runoff source for Totten Reservoir. The tail-water releases and return flows average about 5 cfs over the period April 15 to October 15. An additional 800 acre-ft/year of water in McPhee Reservoir has been identified as available for release to Totten Reservoir depending on water quality needs.

Hydrologic Budget

The water balance, or hydrologic budget, of a lake is the net difference between total inflow, total outflow and evaporative loss. Surface runoff, precipitation and groundwater infiltration are all sources of water inputs. Evaporation and outflow are the main sources of water loss. The hydrologic budget for Totten Reservoir is complicated by the water diversions that have been the major source of surface runoff to the reservoir since its construction.

Surface runoff for ungauged streams can normally be estimated by applying annual areal runoff rates (acre-ft/mi2/yr) from USGS gauging station data in the vicinity of the watershed of interest. This analysis for the Totten Reservoir watershed is complicated by numerous irrigation diversions in Montezuma County. As a result, information provided by the Bureau of Reclamation, Western Colorado Area Office - Southern Division, in Durango, CO was used to estimate surface runoff. This information, developed as part of extensive hydrologic studies in the area from 1978 to 1980 (USBR, 1988), indicated that surface runoff and groundwater inflows provided approximately 183 acre-ft/yr and 223 acre-ft/yr, respectively, to Totten Reservoir. These runoff rates are in line with runoff rates estimated from USGS gauging stations in Montezuma County.

Average precipitation for the Totten Reservoir watershed was estimated from the 30- year historical rainfall records for Cortez, Colorado reported by the National Oceanic and Atmospheric Administration (Owenby and Ezell, 1992). Hydrologic loading attributable to direct precipitation to the surface of the lake was based on the normal precipitation of 13.21 in/yr and the lake surface area 241 acres. The calculated gross annual hydrologic load resulting from rainfall on surface of Totten Reservoir surface is 265 acre-ft/yr.

Evaporation from the lake surface must also be included to determine the role of net precipitation on the lake's hydrologic budget. Water loss due to evaporation is dependent upon a number of variables, including ambient temperature, intensity of sunlight, and relative humidity, and is thus seasonally dependent. A free water surface evaporation rate of 50 in/yr was estimated from maps provided by Farnsworth et al. (1982). This value was used to calculate an evaporative water loss of 1,004 acre-ft/yr from Totten Reservoir. Evaporative losses were subtracted from rainfall to obtain a net average precipitation loss of 739 acre-ft/yr.

Water enters Totten Reservoir primarily via diversions from irrigation projects. Under current operating practices, tail-water releases from the Goodland Ditch average about 5 cfs from April to October (Nunn, 1998). This is equal to an annual contribution of 1,785 acre-ft/yr. The estimated Totten Reservoir hydrologic budget is summarized in Table 1. This budget does not include the additional 800 acre-ft/yr of water from McPhee Reservoir that is potentially available.

The calculated annual discharge from Totten Reservoir is 1,452 acre-ft/yr for current operating conditions. The hydraulic residence time would be 2.3 years without the McPhee flow and 1.5 years with it. The hydraulic residence time prior to 1992, when diversions supplied a total inflow of approximately 6,300 acre-ft/yr, would have been about 0.55 years.

These calculated hydraulic residence times should be conservative because they assume a volume for Totten Reservoir of 3,300 acre-ft. A volume of 3,300 acre-ft combined with the Totten Reservoir surface area of 241 acres results in a calculated mean depth of 13.7 feet, which seems high for the observed maximum depth of 21 feet. It is likely that Totten Reservoir has lost volume since 1965, and the actual hydraulic residence time would decrease in direct proportion to the loss of lake volume.

If necessary, McPhee Reservoir could supply additional water to Totten Reservoir through the Dolores Tunnel. According to the MVIC (Nunn, 1998), this source can provide up to 40 cfs (79 acre-ft/day) without significant erosion concerns. These releases can only be made during the allotted spill period of mid-April to early July, and then only if there is a sufficient volume of water available in McPhee Reservoir. This source could potentially supply up to 4,760 acre-ft of water to Totten Reservoir during a release period of 60 days at the full volume of 40 cfs. This is over 1.4 times the lake volume.

Lake and Stream Water Quality

A field survey of Totten Reservoir and potential water sources for the lake was conducted on April 3, 1998. The potential water sources surveyed included Simon Draw, the main Rocky Ford Ditch inlet to Totten Reservoir, a minor Rocky Ford Ditch branch above the east inlet to Totten Reservoir, and McPhee Reservoir near the Dolores Tunnel. A Hydrolab Surveyor II was used for field measurements of temperature (Temp.), dissolved oxygen (D.O.) concentration, conductivity (Cond.) and pH. Sampling station locations for the April 3, 1998 samples and results of field measurements are summarized in Table 2.

There was no evidence of thermal stratification in either lake on the sampling date. Temperature differences between surface and bottom waters were small in both lakes; however, the water temperature in McPhee Reservoir was 3 to 4° C lower than temperatures in Totten Reservoir. Dissolved oxygen concentrations and pH levels were also relatively constant with depth in both lakes, and values for these parameters were similar in the two lakes, as well as in the three streams sampled.

Runoff from a heavy snowfall the day prior to sampling appeared to be affecting runoff in Rocky Ford Ditch east of Lakewood School; flow was high (est. 2-3 cfs) in this tributary. In contrast, there was little flow (est. <0.5 cfs) in either the Rocky Ford Ditch tributary above the east inlet to Totten Reservoir or Simon Draw. Both of those locations also had cattle upstream from the site, and the main branch of Rocky Ford Ditch had both cattle and sheep upstream.

Conductivity in Totten Reservoir was high on the sampling date, ranging from 1,405 to 1,409 µS/cm. Previous reports on the area (Butler et al., 1994; 1997; U.S. DOI, 1992; unpublished fish survey data from 1981 to 1990) indicated that conductivity in Totten Reservoir, as well as in area streams, is usually at annual high levels in April prior to the start of the irrigation season in May and June. Conductivities in McPhee Reservoir were much lower, with a range of 233 to 235 µS/cm. Conductivity in the main Rocky Ford Ditch was also low, with a value of 386 µS/cm, possibly as a result of snowmelt. In contrast, the smaller Rocky Ford Ditch tributary and Simon Draw both had conductivities above 2,000 µS/cm.

Samples from Totten Reservoir, McPhee Reservoir, Rocky Ford Ditch and Simon Draw were collected for laboratory analyses of nutrients, alkalinity, and total hardness (Table 3 and Appendix A). Totten and McPhee Reservoir samples were collected from the lake surfaces, which should be representative of whole-lake conditions since both reservoirs were well-mixed on the sampling date. A sample for analysis of these same parameters was also collected from Ritter Draw on April 17, 1998. As with the field monitoring results, concentrations of most parameters were generally lowest in McPhee Reservoir and highest in Simon Draw.

Additional samples were collected in Totten Reservoir for analyses of chlorophyll a, phytoplankton and zooplankton. Chlorophyll a and phytoplankton were analyzed in a 0 to 3 m composite sample, while zooplankton were collected with vertical tows over the entire depth of the water column.

There was a relatively high concentration of small microflagellates present on the sampling date, but the phytoplankton assemblage also contained diatoms and chrysophtes which are typically common in reservoirs during the colder months, as well as some green algae. The chlorophyll a concentration of 2.04 µg/L is indicative of low primary productivity. A cladoceran, Daphnia galeata mendotae, was the most common zooplankton, but zooplankton were not present in high numbers. Complete results of the phytoplankton and zooplankton analyses are included in Appendix B.

Previous fisheries studies had listed either emergent, submerged or floating plants as being present at severe levels. There were no signs of aquatic plants on the sampling date, but they may appear later in the season.

Previous studies (unpublished fishery studies, 1981-1990; Butler et al., 1994; 1997; U.S. DOI, 1992) reported results from extensive studies of Totten Reservoir and the surrounding area as part of the Dolores Project. Those reports included results on major ion composition, trace metals and pesticides in water, sediment and biological samples. Samples were also collected by the Bureau of Reclamation from two locations in Rocky Ford Ditch above Totten Reservoir on March 25, 1998, and analyzed for a variety of metals and inorganic ions. Results of these analyses are also included in Appendix A.

Results of selected analyses from previous studies on Totten Reservoir are summarized in Table 4. Conductivity, pH, alkalinity and total hardness levels were reported for several dates between 1981 and 1990 from fishery studies and by Butler et al. (1994). All other results are from two sampling dates (April 17 and November 8, 1990) reported by Butler et al. (1994). Apparently, few water quality samples have been collected since 1992 when Totten Reservoir was taken out of the regional irrigation system and began to operate under current flow conditions; however, results of this study are consistent with the previous results.

No samples from Totten Reservoir exceeded applicable water quality standards. Based on conductivity, however, total dissolved solids (TDS) concentrations, which can be estimated as TDS (mg/L) = 0.65 x conductivity (µS/cm), levels, would exceed the secondary maximum contaminant level (SMCL) of 500 mg/L for TDS in drinking water supplies on some dates in Totten Reservoir and many other area water bodies. This is not of major concern since the lake is not used as a drinking water supply. High dissolved solids levels are also of some concern for aquatic life. This is addressed in the next section of the report.

Effects of Total Dissolved Solids on Fisheries

Based on available information, it appears that salinity at Totten Reservoir is only of marginal concern for aquatic life. The available information was evaluated with regard to other reports on this topic. Many of the existing studies have focused on chloride, and the maximum reported chloride concentration in the Dolores Project area of 120 mg/L is well below any existing levels of concern.

The U.S. EPA "Red Book" of water quality criteria (U.S. EPA, 1976) reported results from an early study (Rawson and Moore, 1944) that found several common freshwater fish survived 10,000 mg/L (mg/L = parts per million or ppm) dissolved solids. Rawson and Moore (1944) also suggested that dissolved solids concentrations in excess of 15,000 mg/L were unsuitable for freshwater fish. Another study (NTAC, 1968) cited by the U.S. EPA (1976) recommended maintaining an osmotic pressure at levels less than that caused by a 15,000 mg/L solution of sodium chloride. Indirect effect of TDS on fisheries are caused by elimination of desirable food and habitat plants. Maximum variations of 1 part per thousand (ppt) are recommended for waters with salinities from 0 - 3.5 ppt.

A number of more recent studies have also addressed the impact of salinity on freshwater fish. Primary freshwater fishes are generally tolerant of salinities that greatly exceed those typical of even relatively "salty" freshwaters. Tolerances of largemouth bass (Micropterus salmoides) (Family Centrarchidae) to various saline waters were reported as 12.5 g/L (Courtenay and Roberts, 1973), 12.9 g/L (Tebo and McCoy, 1964), and16.7 g/L 96-hr LC50's (Nelson, 1987). Reed and Evans (1981) (in EPA, 1988) reported a long-term (14-day) salinity LC50 of 8,500 mg/L chloride (approx. 15.4 g/L salinity) for largemouth bass. Tebo and McCoy (1964) found that concentrations of sea water between 10 and 15 percent (3.5 to 5.3 g/L salinity) were suitable for successful development of largemouth bass eggs and fry. Bluegill (Lepomis macrochirus), another Centrarchid, was found to have similar salinity tolerance with a 14-day LC50 of 14.5 g/L (Reed and Evans, 1981 in EPA, 1988). Channel catfish (Ictalurus punctatus) also demonstrated tolerance to salinity. Allen and Avault (1969) and Stickney and Simco (1971) reported long-term survival of channel catfish in ocean waters of 12 and 13.2 g/L. Nelson (1987) reported a 96-hr LC50 for channel catfish of 12.9 g/L in an inland saline water. Reported salinity tolerances of fishes in the Family Cyprinidae included goldfish (Carrassius auratus), fathead minnow (Pimephales promelas), and Colorado squawfish (Ptychocheilus lucius), with 96-hr LC50's of 16.1, 11.9, and 13.1 g/L salinity, respectively (EPA, 1988, based on the formula, Salinity (g/L) = 0.03 + 1.805 x Chlorinity (g/L); Wheaton, 1977; Nelson and Flickinger, 1992). The above values suggest that gamefish found in Totten Reservoir, such as largemouth bass, bluegill, and channel catfish, along with prey items, such as cyprinid minnows, should not be acutely affected by the maximum concentrations of chloride (11 mg/L=0.05 g/L salinity) reported for Totten Reservoir, or even by the maximum chloride concentrations (120 mg/L=0.25 g/L salinity) reported from the Dolores Project area.

Effects of Totten Reservoir salinity on fish food such as invertebrates are less clear. Hart et al. (1991) suggested that adverse effects on freshwater invertebrates occur at salinities as low as 1000 mg/L. The EPA chloride criterion document takes into account sensitivities of invertebrates and plants and has promulgated a freshwater acute value for chloride of 1,720 mg/L (approx. 3.13 g/L salinity) and a chronic value of 226.5 mg/L (approx. 0.44 g/L salinity) (EPA, 1988). Salinities higher than the chronic value are considered unacceptable if a four-day average exceeds the value more than once every three years. No reported results from Totten Reservoir have exceeded this chronic value.

The EPA values may also be under-protective in cases where sodium chloride is not the main chloride. Chlorides of potassium, calcium, and magnesium have been found to be more toxic to freshwater species than sodium chloride in laboratory studies (EPA, 1988). Reported mean acute toxicities (LC50's) for the cladoceran, Daphnia magna, for example, are 2,523 mg/L NaCl, 1,591 mg/L MgCl2, 289 mg/L CaCl2, and 128 mg/L KCl (from EPA, 1988). In field surveys, high concentrations of magnesium were also found to negatively affect rainbow trout (Oncorhynchus mykiss) survival in sulfate-dominated saline lakes in Wyoming (Mitchum, 1971).

Conversely, high calcium concentrations have been reported to increase tolerance to salinity of some freshwater fishes (Davis and Simco, 1978). Literature suggests that salinity effects on Totten Reservoir cannot be fully determined without further evaluation of the major ions present. However, even if all of the maximum chloride concentration reported from the project area (120 mg/L) was in the forms most toxic to Daphnia magna (a chloride sensitive species), only about 6 mg/L of KCl and 183 mg/L of CaCl2 (using K and Ca values from Table 4) would be present. Using the previous stated LC50 values, this would result in a total Toxic Unit value of 0.676, less than the value (1.0 Toxic Units) that would result in an LC50 being reached. Furthermore, it is unlikely that this worse case scenario would be reached because much of the Ca would be bound with sulfate, not chloride.


The hydrologic budget calculated for Totten Reservoir results in an estimated hydraulic residence time of about 2.3 years under current operating practices, compared to 0.55 years when the lake was being used as part of the regional irrigation system. Totten Reservoir loses an average of 1,004 acre-ft of water per year to evaporation, which is nearly one-third of the lake volume. This could potentially lead to a build-up of solids over a long period of time since the hydraulic residence time is greater than one year, although there is no evidence to indicate this is occurring. The lake has been off-line since 1992, but water quality at the time of the current study was comparable to that reported for spring samples collected from 1981 to 1990.

No water quality samples from Totten Reservoir have exceeded applicable water quality standards. The major concern would appear to be dissolved solids (conductivity), but the warm water fish present in the lake are tolerant to high concentrations of dissolved solids, and spring conductivity levels appear to be the same now as they were in the 1980's.

Additional flushing during spring runoff and spill periods could eliminate even the slight chance of a dissolved solids increase. Water from Simon Draw is much higher in dissolved solids than Totten Reservoir and does not appear to be suitable for this purpose. Water from Ritter Draw appears to be similar in hardness and alkalinity to Totten Reservoir and may not provide much dilution. Water from the main stem of Rocky Ford Ditch may be capable of diluting the dissolved solids in Totten Reservoir, but smaller tributaries to this stream are high in dissolved solids and the flow may not be dependable during the summer months. As a result, diversions from McPhee Reservoir appear to be the most suitable source of dilution water.

Dilution would be most effective if the diverted water was able to completely mix with the water in Totten Reservoir. Mixing would be most complete during the winter and early spring before the lake begins to stratify. Cold water, which has a higher density than warm water, added after Totten Reservoir stratifies would tend to flow as a density current near the bottom of the lake and would not completely mix before being discharged. This consideration is especially important because the April temperatures in McPhee Reservoir were several degrees less than those in Totten Reservoir. Although some warming would occur in transit, and the higher dissolved solids concentration in Totten Reservoir would partially offset the difference in density cause by temperature, the likelihood of complete mixing decreases as temperatures begin to warm.

Additions of cold dilution water could potentially delay spawning for the warm water fish present in Totten Reservoir; however, this does not appear likely based on the limited data available as long as the dilution takes place in early spring. Reported temperatures for Totten Reservoir ranged from 56 to 70°F (13.5 to 21°C) in April and from 62 to 70°F (16.7 to 21°C) in June; no data were reported for May. For comparison, reported temperatures for McPhee Reservoir near the Dolores Tunnel intake were 46.4 to 60°F (8.0 to 16°C) in May and June. Important game fish, such as largemouth bass and bluegill, along with food fish, such as fathead minnows, usually begin spawning in the spring when water temperatures reach 65°F (18°C) (Piper et al., 1983).

A flow rate of 40 cfs would be able to replace the volume of water in Totten Reservoir in about 40 days (3,200 acre-ft), if mixing was complete. If this entire amount is not available, providing this volume for a period of 26 days (1,840 acre-ft) would still result in a complete replacement of Totten Reservoir water on an annual basis when combined with the calculated annual discharge of 1,452 acre-ft. Adding this water as early as possible during the period between April 1 and May 15 would eliminate most of the concerns over incomplete mixing caused by density currents and potential effects on fish spawning.

Based on the evaluation of available data, flushing may not be required every year. Dilution during periods when excess water is available for spills should be sufficient to keep dissolved solids concentrations in Totten Reservoir near current levels except during periods of extended drought. Measurement of conductivity during the spring, when the lake is completely mixed, provides a simple means of checking the dissolved solids concentration and the potential need for dilution.


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