Kansas Geological Survey, Open-file Report 2008-13
Part of the Phreatophyte Research Project Project
by
James J. Butler, Jr., Gerard J. Kluitenberg, and Donald O. Whittemore
KGS Open File Report 2008-13
Prepared for the Kansas Water Office
August 2008
The primary objective of this project was to use water-table fluctuations to estimate the impact of various salt-cedar control activities on the ground-water resources of the Cimarron River alluvial aquifer at a site in Clark County, Kansas. Previous work by this research team has shown that diurnal (daily) fluctuations in the water table can be utilized both as a diagnostic indicator of phreatophyte activity and for quantifying ground-water consumption by phreatophytes. This contract was developed to extend the work of the team to exploit an opportunity presented by a Kansas Alliance of Wetlands and Streams (KAWS) demonstration project focused on investigating the effectiveness of various salt-cedar control measures. Funding for this contract was provided by the Kansas Water Plan through the Kansas Water Office. This contract was supplemented by funds from the Kansas Water Resources Institute and the Kansas Geological Survey.
The KAWS demonstration project is being carried out in an area of salt-cedar infestation along the Cimarron River south of Ashland, Kansas. Four experimental plots were established in pasture on the north side of the Cimarron River. One plot (Plot 1) is used for monitoring background (unaltered) conditions, while the other three plots (Plots 2-4) are for application of different salt-cedar control measures. Application of control measures began in mid-March of 2005 and is continuing. The first total clearing of salt cedars (mulch cutting) from Plots 2 and 3 was completed on August 9, 2005. Treatment of salt-cedar regrowth in Plot 2 with a herbicide-diesel mix was completed in mid-August of 2005. Plot 3 was cut again shortly after the end of this reporting period.
Six shallow wells were installed in Plots 1-3 in August 2004. All wells have submersible pressure sensors to allow monitoring of water levels at a 15-min interval. A weather station was installed in October 2004 to monitor meteorological conditions at the same 15-min interval and provide estimates of the potential for evapotranspiration on a daily basis. A neutron-probe access tube was installed adjacent to each well in August 2004 to allow measurement of the volumetric water content above the water table. Water content is measured approximately biweekly during the growing season.
The relative ground-water savings gained through the control activities were estimated using a ratio method specifically developed for this project by the research team. The method is based on diurnal water-table fluctuations and ratios of the empirical equation of White [1932]. Application of this method to data from wells in Plots 2 and 3 showed that ground-water consumption was reduced, relative to what would have been expected in the absence of the control activities, by 23-56% (three-well average of 40%) one month after the total clearing of the salt cedar in Plots 2 and 3. A follow-up analysis using data from June 2006, ten months after completion of treatment, showed that ground-water consumption in Plots 2 and 3 during that period was reduced by 2-27% (three-well average of 17%). Thus, the reductions in ground-water consumption achieved from salt-cedar control appear to be decreasing with time, despite the severe drought conditions experienced during the 2006 growing season at the site. This decreased reduction may be a result of increased growth (and thus water use) of grasses, forbs, and small bushes due to greater exposure to sunlight and wind after the removal of the large phreatophytes, and regrowth of salt cedar. Further work is needed to assess the relative importance of ground-water consumption by these and other mechanisms to better understand the impact of the control measures.
These results demonstrate that long-term monitoring is critical for assessing the ultimate ground-water savings gained through salt-cedar control. If control activities are undertaken for the express purpose of "salvaging" ground water, monitoring networks, such as that established for this project, must be in place prior to commencement of control activities so that the hydrologic impact of those activities can be assessed. Collection of water-level, water-content, and meteorologic data will continue at this site as long as funding permits in order to ascertain the ultimate ground-water savings achieved with the control activities.
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Kansas Geological Survey, Geohydrology
Placed online Oct. 3, 2008
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