Cheney Reservoir and Water Quality Studies

Science Center Objects

Cheney Reservoir is located on the North Fork Ninnescah River in south-central Kansas, 20 miles west of Wichita. Cheney Reservoir is the primary drinking water supply for the city and a popular recreational resource for the region. After cyanobacterial blooms in 1990 and 1991, which caused servere taste-and-odor events, the USGS Kansas Water Science Center partnered with the City of Wichita  and began studies to better understand and improve the water-quality of Cheney Reservoir because of the potential economic and public health concerns for drinking water and recreational activities. “Knowledge gained from USGS studies in the Cheney Reservoir Watershed has assisted in the development, implementation, maintenance, and assessment of watershed-management goals and plans. This data has allowed us to ensure a safe and reliable water supply and put us ahead of the curve in terms of sediment management.” – Don Henry, Assistant Director of the City of Wichita’s Public Works and Utilities, 2017.

Early Studies

During 1996 to 2001 efforts were made to study the loading of contaminants, nutrients, and sediment to Cheney Reservoir from the watershed. A network of study sites, along with two continuous water-quality monitoring sites and collection of sediment cores, were used to analyze subwatershed sources of nutrient and sediment loading from the watershed into Cheney Reservoir.

Continuing Reservoir Studies

Starting in 2001, the focus of the studies shifted focus to analyzing suspended sediment and nutrient concentrations; presence of cyanobacteria, cyanotoxins and taste-and-odor compounds; and enviromental variables (specific condunctance, pH, temperature, turbidity, dissolved oxygen, and chlorophyll). The data is collected through the use of continuous water-quality monitoring and discrete sampling.

Watershed Studies

As part of the efforts to assess water quality in Cheney Reservoir, a Cheney Reservoir Task Force was formed in 1994 to establish water quality standards to quantify primary pollutants (nutrients and sediment) and understand their relation to cyanobacterial blooms. Studies showed that total phosphorus concentrations in the watershed were about three times the natural conditions, an estimated 65 percent of that originating from agricultural sources suggesting long-term goals may not be attainable. As of 2001, sediment accumulation in the reservoir was less than expected. A substantial portion of the accumulation was delivered to Cheney Reservoir during very short time periods with extreme hydrological conditions.

Flow-normalized concentrations and fluxes were computed during 1999 through 2019 using Weighted Regressions on Time, Discharge, and Season statistical models and bootstrap tests. This statistical approach allows for analysis of trends by removing annual hydrologic variability. Flow-normalized concentrations of TSS, SSC, OP, TP, and TOC had upward trend probabilities; conversely, nitrate plus nitrite had a downward trend. Flow-normalized fluxes for OP, TP, and TOC had an upward trend. No discernible patterns were identified for flow-normalized flux of TSS or suspended sediment. Nitrate plus nitrite flow-normalized flux indicated a downward trend.

Flow-normalized concentrations for TSS were less than the Cheney Reservoir Task Force long-term goal of 100 milligrams per liter (mg/L), but the upward trend indicated the long-term goal may be exceeded if no changes are made. Flow-normalized TP concentrations exceeded the CRTF long-term goal (0.1 mg/L) and had a very likely upward trend. Flow-normalized nitrate plus nitrite concentrations exceeded the CRTF long-term goal of 1.2 mg/L during the beginning of the study period, then were less than the Cheney Reservoir Task Force goal for the remainder of the study; however, during 2010–19 flow-normalized concentrations were increasing.

Continuing Reservoir Studies

During 2001 through 2016, the U.S. Geological Survey, in cooperation with the city of Wichita, conducted a study to develop reliable tools to estimate the onset of cyanobacterial-related taste-and-odor occurrences in Cheney Reservoir. cyanobacteria and microcystin concentrations in Cheney Reservoir showed seasonal patterns, however the abundance and concentration varied by orders of magnitude across years. Peaks were seen in late summer or early fall with smaller peaks seen in December. Seasonal patterns were less consistent but present for the taste-and-odor compound geosmin. Water quality models were developed based on hourly measurements since 2001; the models are available at the USGS National Real-Time Water Quality website at These models demonstrate the need for continuous reevaluation of toxin and taste-and-odor models due to changing environmental conditions.