U.S. Geological Survey
Water-Resources Investigations Report 00-4126
Prepared in cooperation with the
CITY OF WICHITA, KANSAS, as part of the
Equus Beds Ground-Water Recharge Demonstration Project
Download this report as an HTML file
(132 KB)
Regression Analysis and Real-Time Water-Quality Monitoring to Estimate Constituent
Concentrations, Loads, and Yields in the Little Arkansas River, South-Central Kansas, 1995-99
By V.G. Christensen, Xiaodong Jian, and A.C. Ziegler
Abstract
Water from the Little Arkansas River is used as source water for artificial recharge to the
Equus Beds aquifer, which provides water for the city of Wichita in south-central
Kansas. To assess the quality of the source water, continuous in-stream water-quality
monitors were installed at two U.S. Geological Survey stream-gaging stations to provide
real-time measurement of specific conductance, pH, water temperature, dissolved oxygen, and
turbidity in the Little Arkansas River. In addition, periodic water samples were collected
manually and analyzed for selected constituents, including alkalinity, dissolved solids,
total suspended solids, chloride, sulfate, atrazine, and fecal coliform bacteria. However,
these periodic samples do not provide real-time data on which to base aquifer-recharge
operational decisions to prevent degradation of the Equus Beds aquifer.
Continuous and periodic monitoring enabled identification of seasonal trends in selected
physical properties and chemical constituents and estimation of chemical mass transported in
the Little Arkansas River. Identification of seasonal trends was especially important because
high streamflows have a substantial effect on chemical loads and because concentration data
from manually collected samples often were not available. Therefore, real-time water-quality
monitoring of surrogates for the estimation of selected chemical constituents in streamflow
can increase the accuracy of load and yield estimates and can decrease some manual
data-collection activities.
Regression equations, which were based on physical properties and analysis of water samples
collected from 1995 through 1998 throughout 95 percent of the stream's flow duration, were
developed to estimate alkalinity, dissolved solids, total suspended solids, chloride,
sulfate, atrazine, and fecal coliform bacteria concentrations. Error was evaluated for the
first year of data collection and each subsequent year, and a decrease in error was observed
as the number of samples increased. Generally, 2 years of data (35 to 55 samples) collected
throughout 90 to 95 percent of the stream's flow duration were sufficient to define the
relation between a constituent and its surrogate(s). Relations and resulting equations were
site specific.
To test the regression equations developed from the first 3 years of data collection
(1995-98), the equations were applied to the fourth year of data collection (1999) to
calculate estimated constituent loads and the errors associated with these loads. Median
relative percentage differences between measured constituent loads determined using the
analysis of periodic, manual water samples and estimated constituent loads were less than 25
percent for alkalinity, dissolved solids, chloride, and sulfate. The percentage differences
for total suspended solids, atrazine, and bacteria loads were more than 25 percent.
Even for those constituents with large relative percentage differences between the measured
and estimated loads, the estimation of constituent concentrations with regression analysis
and real-time water-quality monitoring has numerous advantages over periodic manual sampling.
The timely availability of bacteria and other constituent data may be important when
considering recreation and the whole-body contact criteria established by the Kansas
Department of Health and Environment for a specific water body. In addition, water suppliers
would have timely information to use in adjusting water-treatment strategies; environmental
changes could be assessed in time to prevent negative effects on fish or other aquatic life;
and officials for the Equus Beds Ground-Water Recharge Demonstration project could
use this information to prevent the possible degradation of the Equus Beds aquifer
by choosing not to recharge when constituent concentrations in the source water are large.
Constituent loads calculated from the regression equations may be useful for calculating
total maximum daily loads (TMDL's), which States are mandated to establish for stream
segments that have been identified by the 1972 Clean Water Act as limited for specific uses
because of water-quality concerns. Additionally, information on constituent loads and yields
can be used to indicate in which subbasin to concentrate efforts with regard to land-resource
best-management practices. These results have application anywhere constituent
concentrations, loads, or transport are of concern.
Christensen, V.G., Jian, Xiaodong, and Ziegler, A.C., 2000, Regression Analysis and
Real-Time Water-Quality Monitoring to Estimate Constituent Concentrations, Loads, and Yields
in the Little Arkansas River, South-Central Kansas, 1995-99: U.S. Geological Survey
Water-Resources Investigations Report 00-4126, 36 p.
To request a paper copy of this report, email:
GS-W-KS_info@usgs.gov
|