| Title |
Investigators | Department | Objectives | Approach Keywords | Progress Reports | Impact Statements | Publications | |
Project * COL00684 | |
| Title | Defining and Engineering Solutions for Agroecological Threats from Salinity and Selenium in an Irrigated River Valley |
| Investigator(s) | Gates, TK; |
| Department | Civil and Environmental Engineering |
| Objectives | The long-term goal of this research is to redress sub-par water utilization and water quality degradation in the Lower Arkansas River Basin of Colorado through discovery and widespread adoption of water management practices that will (a) reduce detrimental waterlogging and salinity impacts to agriculture in the Arkansas River watershed, (b) enhance water quality in the river by diminishing nonpoint source salinity and selenium (Se) loads, and (c) lead to real water conservation in the river by reducing nonbeneficial upflux from high water tables and extraction by invasive phreatophytes along the river corridor. Efforts are continuing toward discovery of the best solution strategies for the entire river valley. Databases and models are being refined and expanded, working toward a comprehensive set of tools that will support wise water management decisions, not only at the field and regional levels, but also at the river-basin scale. The three major objectives of this research are: (1) refine and apply calibrated regional-scale flow and solute transport models, to evaluate proposed solution strategies based upon sound field data (A major emphasis will be placed on characterizing and controlling Se pollution, in conjunction with salinity. The impacts of alternative strategies will be comparatively ranked in a manner that is congruent with measured processes in representative Valley regions both upstream and downstream of John Martin Reservoir. Regional-scale solutions will be checked with field-scale models to help insure their practicality on individually-managed field units.); (2) refine and apply a GIS-centered basin-scale decision-support model, now under development, to assess the likely impacts of regional solutions on river flows and concentrations and to explore ways of operating the river to make possible regional scale solutions that will comply with Colorado water rights and with interstate compact; and (3) design small-scale pilot programs, in cooperation with Valley farmers and agencies, under representative canal command areas to field-test and refine top-ranking solution strategies. |
| Approach | This project will support on-going data collection in two representative regions along the Lower Arkansas River (one upstream and one downstream of John Martin Reservoir), providing an enhanced understanding of the nature and extent of agroecological problems and a sound foundation for reliable modeling and evaluation of alternative solutions. Continued investigations in these study regions will include monitoring of water table depth, salinity, and selenium; measurement of water level, salinity, and selenium in the river, tributaries, irrigation canals, and drains; measurement of soil salinity; measurement of hydraulic conductivity of near-surface soils and of seepage from canals; and collation and analysis of other data. Regional-scale and basin-scale models for simulation flow and solute transport processes along the river valley will be enhanced and completed. Simulated baseline conditions will be compared to conditions simulated for considered solution alternatives for both the upstream and downstream study regions. Using data and methods developed in the initial phases of this project, the GMS model will be applied to systematically predict, among other things, water table depth and salinity, soil salinity, crop yield, rate and concentration of ground water return flows to the river, and nonbeneficial consumptive use under fallow land in response to a suite of discrete improvement alternatives to be adopted. Concentrations of dissolved Se in the water table aquifer and associated transport to the river will also be incorporated into the model. Alternative strategies to be considered include increased irrigation efficiency, reduced seepage from irrigation canals, increased pumping rates from existing pumping wells with excess flows (above legal permit) routed through drains to the river, installation of horizontal subsurface drains, lowering of water surface elevation along the river, eradication of invasive phreatophytes along the river corridor, and combinations of these strategies. Modeled strategies will be checked within the upstream and downstream study regions using the CSUID field-scale model. If predicted field-scale performance is not acceptable, adjustments will be made until solutions can be obtained for which acceptable performance is achieved. The enhanced MODSIM basin-scale model, currently under development in the context of a basin-scale spatial decision-support system, will be extended and applied to explore ways of operating the river to enable regional-scale solutions that will comply with Colorado water rights and interstate compact agreements. Continued use of artificial neural networks to embed complex stream-aquifer interactions, as well as surface runoff, into the modeling system will be pursued. Calibration of MODSIM will be completed in two stages: hydrologic calibration and institutional/administrative calibration. Small-scale pilot programs will be designed for final assessment and refinement of strategies for large-scale implementation of sustainable and effective water management changes. |
| Keywords | salinity, selenium, irrigation induced salinity, irrigation induced pollution irrigation, irrigation management, drainage, groundwater model salt-transport model, river basin salinization, river basin management waterlogging, decision support system |
| Progress Reports | |
| 1997 | Inefficiency in irrigation practices has intensified problems of elevated water tables and high salinity levels to the point where approximately 36,000 hectares of agricultural land is taken out of production each year in Colorado. Evaluating the economic and environmental outcomes of best management practices (BMP's) for alleviating these problems is hindered by the hydrologic, geohydrologic, geochemical and administrative (legal) complexities of appropriative river basin systems. A decision support system (DSS) is needed which will enable water managers and policy makers to evaluate the integrated water quantity/quality impacts of BMP's on a basin-wide scale. This study extends previous work on a Colorado Agricultural Experiment Station project which resulted in development of the integrated water quantity/quality river basin management model MODSIMQ. This current study attempts to incorporate into MODSIMQ recent scientific advances in stream-aquifer modeling, groundwater flow and solute transport, and prediction of agricultural return flow water quality. A powerful graphical user interface is being designed to integrate all of these features with complex water rights, interstate compact, and other legal issues that control allocation and use of both surface water and groundwater in appropriative river basins. This study makes use of geographic information system (GIS) technology for creating the spatial data base required for implementation of the groundwater flow and solute transport model for application to the Lower Arkansas River Valley in Colorado as a case study. Extensive field experiments and data collection, including aerial photos and LANDSAT imagery, provide the basis for model calibration and verification in support of detailed investigations on economic and environmental impacts of the implementation of various BMP's in the basin. Active participation in the Arkansas River Basin Technical Group, comprised of representatives from various agencies addressing salinity problems in the Valley,has greatly reinforced the practical relevance of this study. A detailed review of the Highly Integrated Model (HIM) of the Lower Arkansas River Valley was conducted in cooperation with the Office of the State Engineer, since it played a major role in the recent legal action between Colorado and Kansas over apportionment of Arkansas River waters. A statistical analysis of cropping patterns in the Valley has been completed, along with a digital base map of basin agriculture for incorporation into a GIS to be linked with the DSS. Ongoing work includes transfer of all geo-spatial data into the GIS, construction of the groundwater flow and solute transport model , and appropriate modification of MODSIMQ. The results of this study will enable evaluation of BMP's on a basin-wide scale that minimize environmental degradation without harming the agricultural economy. The creation of a tool which addresses problems on a basin-wide scale, while allowing for the modeling of localized changes, should have far-reaching scientific impacts in assessing the most effective BMP's for investigations in other river basins. |
| 1998 | Within Colorado, inefficient irrigation, inadequate drainage, and certain river basin operational practices have intensified problems of elevated groundwater tables and salinity levels resulting in agricultural lands being taken out of production and many more affected by crop yield reduction. Characterizing the extent and intensity of the salinization threat is difficult due to a dearth of available water quality, soil salinity, and groundwater data. Evaluating the economic and environmental outcomes of best management practices (BMP's) for alleviating these problems is hindered by the geohydrologic, geochemical and administrative complexities of appropriative river basin systems. Focusing on the Lower Arkansas River Basin in Colorado as a case study, this project is an attempt to acquire and collect the necessary data for characterizing the seriousness of the salinity problem, as well as to develop a model-based decision support system (DSS) for enabling water managers and policy makers to evaluate the integrated water quantity/quality impacts of BMPs for salinity control on a basin-wide scale. A significant achievement of this project has been the collection of soil salinity data in thirty fields of ten to twenty acre sizes over a significant portion of the study area using a Geonics EM 38 probe, with measurements verified from laboratory analysis of the saturation extract taken from soil samples in these fields. Preliminary analysis shows field-averaged soil salinity of up to 7600 mg/l, with an average of 2200 mg/l over the fields surveyed. These values are indicative of up to 90% crop yield reductions, with an average reduction of about 15 to 20%. Measurements taken to date in 15 observation wells indicate an average water table depth of only 1.5 m below the land surface, with depths as shallow as 0.30 m in some locations. EC measurements taken at these observation wells average around 2400 mg/l , with similarly high values observed at numerous reservoirs, canals, and drainage ditches in the study area. GPS measurements of spatial locations and elevations have been obtained at all data collection sites for input into a GIS-based two-dimensional numerical model of shallow groundwater flow and salt transport in the study area between Manzanola and the Otero-Bent county line. The model is an implementation of the Department of Defense Groundwater Modeling System (GMS 2.1), which acts as an interface for data entry into the USGS MODFLOW and EPA MT3D models. Processed Landsat TM data for the study area serve as background images useful for model construction, and also aid in the interpretation of model data and results. Numerous spatial data layers created and input into GMS 2.1 include: digitized field boundaries, the surface water distribution system, ground surface elevations, aquifer bottom elevations, water table elevations, and hydraulic conductivity data. Preliminary runs have been completed, indicating that the model-based DSS will enable evaluation of BMP's for salinity control on a basin-wide scale and allow for wise long-term planning for sustainability of agriculture in the Lower Arkansas River Valley. |
| 1999 | The study region for this project straddles a 40-km reach of the lower Arkansas River in Colorado, encompassing about 20,000 hectares of irrigated land. Water table depth and salinity were measured weekly or bi-weekly in 88 monitoring wells over the region in the summer of 1999 . Surface-water salinity was measured weekly to bi-weekly at more than 160 locations in the Arkansas River, 7 major canals, 7 drains, and 2 off-stream reservoirs. Soil salinity was measured in 30 fields in Otero County over the summer of 1998, and in 68 fields in Otero and Bent Counties over the summer of 1999. High precision GPS equipment was used to locate each ground-water and surface-water sampling site for analysis in a GIS. Slug tests for determining hydraulic conductivity were conducted at 67 locations within the study subregion, with hundreds of soil samples collected for estimating soil texture with depth. Also, actual crop yield losses were estimated through harvest records on many of the fields that have been studied. Preliminary analysis of data reveals seasonal-average water table depth of around 1.5 m below ground surface over about 70% of the subregion. Seasonally-averaged electrical conductivity (EC) of the ground-water was around 3.9 dS/m (3100 mg/l), which is classified as moderately saline for irrigation purposes. Seasonally-averaged EC measured at 8 locations along the River ranged from 0.86 dS/m (602 mg/l) at the upstream end of the study reach to 1 .50 dS/m (1050 mg/l) downstream. Average EC in irrigation canals was 0.93 dS/m (651 mg/l), indicating slight restriction in use for irrigation. Seasonally-averaged EC measured in open drains returning to the river was around 2.6 dS/m (1820 mg/l). Thirty to 90 measurements of soil salinity were collected within each sampled field (to a depth of about 1 meter) early and late in the growing season using GeonicsTM EM-38 electro-magnetic induction probes. Sampling early in the season revealed field-averaged values ranging between 0.5 to 18 dS/m (350 to 12 ,600 mg/l ), which averages to 2.7 dS/m (1890 mg/l) over the 68 fields surveyed. This average increases to 2.8 dS/m (1960/mg/l) for the late season measurements. Measured soil salinity values during the 1998 and 1999 seasons are indicative of field-averaged crop yield reductions up to 90 %, with average reductions ranging from 10 to 20%. In addition to salinity effects, adverse impacts on crop yields are also likely occurring due to waterlogging associated with shallow water tables. In addition to field measurements, work has advanced in developing and applying a numerical finite-difference model of shallow groundwater flow and salt transport to assess strategies for solving saline-high-water-table problems inside the study subregion. Effective long-term solutions will require irrigation systems that deliver and apply appropriate quantities of water to meet crop needs and to leach excess salts from the soils. At the same time, drainage systems must be designed and maintained to remove a fraction of the leachate so as to sustain desirable water table depths and minimize return flow of salts back to the root zone due to capillary rise. |
| 2000 | The current study subregion extends eastward about 60 km along the Arkansas River, from Manzanola in Otero County to Adobe Creek in western Bent County, encompassing about 26,400 ha of irrigated land. Depth and salinity (TDS) of the water table were measured on a weekly to bi-weekly basis in 111 monitoring wells over the region during summer 2000. Surface-water salinity was similarly measured at more than 173 locations, including 10 points in the Arkansas River, six major canals, 12 drains, and two off-stream reservoirs. Soil salinity was measured in 75 fields over summer 2000. GPS equipment accurately located each of the groundwater and surface water sampling sites for use in a GIS. Slug tests for hydraulic conductivity were conducted at 95 locations, along with hundreds of soil samples collected for estimating soil texture with depth. In summer 2000, average water table depth over the subregion increased about 2.5 m. Seasonal-averaged EC of the shallow water table was about 3.2 dS/m in 2000, representing a moderate to high saline classification for irrigation purposes. Seasonally-averaged EC measured at eight locations along the Arkansas River ranged from 0.86 dS/m at the upstream end of the study reach to 1.50 dS/m at the downstream end. Average EC in the irrigation canals was 0.93 dS/m, indicating slight restriction in use for irrigation. Seasonally-averaged EC measured in open drains was about 2.6 dS/m. About 20 to 100 measurements of soil salinity were made within each sampled field (one meter depth) both early and late in the 2000 growing season using EM-38 probes. Preliminary analysis of early-season sampling revealed field-averaged values ranging from about 0 to 15.2 dS/m, with an average of 2.6 dS/m over the 74 fields surveyed. For the late season, the overall average was about 2.0 dS/m over 77 fields. These results indicate up to 15% field-averaged crop yield reductions due to salinization, translating into revenue losses of up to $125/ha, based on current crop prices. These data are input to the GMS model for assessing strategies for solving saline-high-water-table problems inside the representative subregion. The finite-difference grid within the subregional model defines homogeneous cells averaging about 6 ha size. Lines defining streams, canals, and drains are discretized at scales of about 200 to 300 m. Preliminary modeling suggests only limited improvement can be expected from vertical drainage due to increased pumping, or decreased recharge from reduced overirrigation. Such results show GMS to be a useful tool for developing preliminary solution strategies at the subregional scale, such as canal lining, horizontal subsurface drainage, and improved river conditions. However, localized strategies must be fully integrated into plans for managing river flows and salinity at the basin scale. Through hierarchical modeling, strategies developed at the subregional scale will be evaluated upscale by a basin-scale model. Such evaluation, along with farmer and agency input, will provide feedback for refinement and final recommendations for target strategies. |
| 2001 | The current study subregion encompasses about 26,400 hectares of irrigated land in the lower Arkansas River Valley in Colorado. More than 100 monitoring wells have now been installed and are routinely measured. Preliminary results from the 2001 season indicate an average depth to water of about 8.8 ft. The average measured salinity (as electrical conductivity, EC) of the water table in the study region was about 3.0 dS/m (2700 mg/l) in 2001. Surface-water salinity is routinely measured at more than 170 locations, including points in the Arkansas River, in six major canals, in twelve drainages, and in two reservoirs. Data from the 2001 season are still under analysis. Analysis of 1999 data indicated that the seasonal average rate of groundwater return flow to the river (directly and through tributary drainages) was computed as 5.5 million m3/week, with an accompanying diffuse salt loading rate of 16.2 million kg/week (about 740 kg/week per irrigated ha). Soil salinity (to a depth of about 1 m) was measured in early June and in mid August on 80 fields in 2001 using electromagnetic induction probes at an average of 62 locations per field. Data collected in 2001 are currently under analysis. For the late-season readings in 1999, about 70% of fields had at least 25% of measured points above the salinity threshold, indicating significant soil degradation and declining yield. Crop yield reduction due to salinization was estimated to range between 0 and 75% on fields spread over the subregion, averaging about 10%. Additional losses are likely occurring due to waterlogging. Steady-state modeling, to estimate long-term equilibrium conditions, indicates that increased pumping of existing well facilities would result in only limited localized improvement. Reduced recharge through increased irrigation efficiency would provide more extensive benefits, especially in much of the area south of the river. Reductions in recharge of 20% or 33% were deemed feasible through improved irrigation management such as altering timing of irrigations and flow rates applied to the field. A 20% recharge reduction would cause an average reduction in water table elevation of about 0.36 m but would result in a negligible change in average equilibrium groundwater salinity. A 33% recharge reduction would result in an average reduction in water table elevation of about 0.62 m. Such a reduction would likely significantly reduce the salinity of overlying soils. Salt loads in return flows to the river should be reduced by about 14%, due primarily to reduced transport of salts dissolved from marine shale deposits. Though reduced salt load is a perceived benefit, the timing of reductions in groundwater return flows must be carefully considered in an unsteady flow model to evaluate potential impacts on flows available to downstream users. Also, it has been found that lowering the saline water table in the most severely-affected areas will require more than simply increasing irrigation efficiency or increasing pumping rates. Costlier strategies will need to be considered, such as canal lining, horizontal subsurface drainage, and lowering of the river level. |
| 2002 | Water table depth and salinity were measured throughout 2002 in 102 monitoring wells in the upstream study subregion in the vicinity of La Junta, Colorado. Due to drought conditions, about 58% of the wells were dry by the end of August. Preliminary results indicate an average measured water table depth over the 2002 irrigation season of about 2.80 m, an average increase of about 1 m compared to depths measured in 2001. The average measured water table salinity over the season was about 3.17 dS/m (2800 mg/L) in 2002, an average decrease of 0.46 dS/m (410 mg/L), compared to 2001. Surface-water salinity was routinely measured at more than 170 locations, including eight locations in the Arkansas River. Data from the 2002 season are still under analysis. In the downstream study subregion in the vicinity of Lamar, Colorado, 112 monitoring wells were routinely measured. About 53% of the wells were dry by the end of September. Preliminary estimates of measured water table depth and salinity were 3.05 m and 4 .86 dS/m (4300 mg/L). Surface-water salinity was measured at about 120 locations, including six locations along the river. Soil salinity was measured early and late in the irrigation season on 80 fields in the upstream area and on 80 fields in the downstream area in 2002. Data are currently under analysis. Horizontal saturated hydraulic conductivity was measured by slug test in 47 monitoring wells in the downstream study area. Also, nine deep boreholes were drilled downstream. About 50 monitoring well locations and 19 surface water locations (including four along the river) were selected to begin sampling for dissolved selenium and iron in the downstream area. Dynamic modeling of the upstream study subregion was conducted to predict impacts of reduced recharge through increased irrigation efficiency and decreased canal seepage. Results suggest that substantial reductions in water table elevation and in salt loads in return flows to the river could be achieved. For example, a reduction of recharge from overirrigation by 50% would have reduced the average water table elevation by about 0.45 m over the period 1999 - 2001. A 75% reduction in seepage losses from canals was predicted to result in about a 0.70 m reduction. Respective reductions in the salt load in return flows to the river were predicted as about 20% and 25%. Results also suggest that nonbeneficial consumptive use from shallow water tables under fallow fields would be reduced. Impacts of other alternative improvements, including subsurface drainage, are under consideration. In addition, progress was made in development of a model for predicting basin-scale impacts of alternatives. All tributaries, gaging stations, diversions, and storage facilities along the Arkansas River have been incorporated in the model, along with their associated water rights designations. Linkages between the subregional scale model and the basin-scale model, have been initially developed using a neural network. |
| 2003 | Water table depth and salinity were measured throughout 2003 in 102 monitoring wells in the study region in the vicinity of La Junta, Colorado. Water table elevations rose slightly compared to 2002 conditions, due to improved water availability. However, drought conditions continued. Preliminary results indicate average measured water table depths over the 2003 irrigation season of about 2.77 m in the study region. The average measured water table salinity over the season was about 2.8 dS/m in 2003. About 48% of the wells in the study region were dry as a result of the drought. Surface-water salinity was routinely measured at more than 170 locations in the study region, including eight locations in the Arkansas River. Data are still under analysis. Soil salinity was measured early and late in the irrigation season on 80 fields in the study area in 2003. Early season results indicated average measured soil salinity of 3.1 dS/m. Data indicate that average crop yield reduction due to waterlogging and salinity ranges from 10 to 20%. Horizontal saturated hydraulic conductivity was measured by slug test in an additional nine monitoring wells in a second study area downstream of Lamar (downstream study area), and seepage tests were conducted in two earthen canals. About 50 monitoring wells and 19 surface water locations (including four along the river) were sampled for dissolved selenium and iron in the downstream area. Though dissolved iron concentrations were low, dissolved selenium was found to be moderately high, often exceeding State standards. Dynamic modeling of the study region was conducted to predict impacts of reduced recharge through increased irrigation efficiency and decreased canal seepage, improved drainage through increased pumping and installation of subsurface drains, and combined interventions. Results suggest that substantial reductions in water table elevation, soil salinity, and salt loads in return flows to the river could be achieved. For example, a reduction of recharge from overirrigation by 50%, along with a 90% reduction in canal seepage, would have reduced the average water table elevation by about 1.5 m over the period 1999 - 2001 and reduced the average soil salinity by about 500 mg/L. Reduction in the salt load in return flows to the river was predicted as 50 to 60%. Progress was made in development of a model for predicting basin-scale impacts of alternatives. All tributaries, gaging stations, diversions, and storage facilities along the Arkansas River have been incorporated in the model, along with their associated water rights designations. The upstream regional-scale model and the basin-scale model have been successfully linked using an artificial neural network, and return flow predictions have been developed and tested. |
| 2004 | Water table depth and salinity were measured throughout 2004 in 102 monitoring wells in the upstream study region in the vicinity of La Junta, Colorado and in 112 wells in the downstream region near Lamar, Colorado. Water table elevations rose in 2004 compared to 2002 and 2003 conditions, due to increased precipitation and improved water availability. Preliminary results indicate average measured water table depths over the 2004 irrigation season of about 3.31 m and 3.97 m in the upstream and downstream regions, respectively. The average measured water table salinity over the season was about 3.3 dS/m (2920 mg/L) upstream and 4.8 dS/m (4260 mg/L) downstream in 2004. About 35% of the wells upstream and 32% of the wells downstream were dry as a result of the continuing drought. Surface-water salinity was routinely measured at more than 150 locations in the upstream study region, including eight locations in the Arkansas River, and at about 100 locations downstream, including six locations in river. Data are still under analysis. Soil salinity was measured early and late in the irrigation season on 68 fields in the upstream area and on 75 fields in the downstream area in 2004. Analysis of soil salinity data is still in process. Calibration equations for the EM38 salinity probe have been developed, based upon 253 calibration sites upstream and 161 calibration sites downstream. About 54 monitoring wells and 21 surface water locations (including six along the river) were sampled for dissolved selenium (Se) and iron in the downstream area. Analysis of data collected in 2003 and 2004 revealed a median Se concentration of 16.7 micrograms/liter in groundwater. River samples revealed a mean Se concentration of 11.2 micrograms/liter with all 64 samples exceeding the Colorado standard. Dynamic modeling of the upstream study region was conducted to predict impacts of reduced recharge through increased irrigation efficiency and decreased canal seepage, improved drainage through increased pumping and installation of subsurface drains, and combined interventions. Predicted average regional decrease in water table elevation was as great as 1 .93 m over the irrigation season. Regional and seasonal average decrease in soil salinity was predicted as high as 950 mg/L. Estimated groundwater salinity changes, reduction in total salt loading to the river (as high as 40 to 45%), increase in average regional crop yield (as high as 10 percentage points), and changes in net water consumption indicate the potential for marked regional-scale enhancements to the irrigation-stream-aquifer system. Progress was made in continued development and testing of a model for predicting basin-scale impacts of alternatives, constrained by state water rights and interstate compact. The upstream regional-scale model and the basin-scale model have been successfully linked using an artificial neural network and have been integrated into a GIS format. |
| 2005 | In 2005, water table depth and salinity were routinely measured in 102 monitoring wells in the Upstream Study Region in the vicinity of La Junta, Colorado and in 110 wells in the Downstream Region near Lamar, Colorado. Water table elevations remained higher in 2005, indicating greater recharge to the water table due to increased irrigation water applications compared to the previous few years of drought. Preliminary results indicate average measured water table depths over the 2005 irrigation season of about 3.51 m and 4.01 m in the upstream and downstream regions, respectively. Average measured water table salinity over the season was about 3.1 dS/m (2740 mg/L) upstream and 4.8 dS/m (4260 mg/L) downstream. Surface-water salinity was routinely measured at about 100 locations in the Upstream Study Region, including 8 locations in the Arkansas River, and at about 100 locations downstream, including 6 locations in river. Typically, river salinity measured downstream was 2 to 4 times greater than that measured upstream. Soil water salinity was measured early and/or late in the irrigation season on 61 fields in the upstream area and on 79 fields in the downstream area in 2005. Average specific conductance in the soil water was 3.7 dS/m upstream and 5.6 dS/m downstream. Data gathered in 2005 on crop yields reveal reductions in corn and alfalfa yields for soil salinity levels exceeding 3 - 4 dS/m. About 54 monitoring wells and 21 surface water locations (including six along the river) were sampled for dissolved selenium (Se) in the downstream area. Analysis of data collected from April 2003 until July 2005 revealed a median Se concentration of 16.4 micrograms/liter in groundwater. Se concentrations measured in the river samples ranged from 4.2 to 23 micrograms/liter with median of 9.4 micrograms/liter, exceeding the Colorado standard. Seepage tests were conducted in five canals in 2005. Results from tests conducted over the entire life of this study indicate substantial seepage loss rates of about 0.5 to 7.4 cfs per mile in four canals tested upstream and about 0.2 to 6.6 cfs per mile in three canals downstream. Calibration of the enhanced regional-scale model of ground water flow for the Upstream Study Region began in June 2005. The enhanced model is first being calibrated for the period April 1999 to October 2001 and will be applied to simulate baseline and improved management strategies for the period April 1999 to October 2004. The model will also be applied downstream to simulate flow, salt transport, and Se transport. Progress was made in continued development and testing of GeoDSS, a spatial decision support model for predicting basin-scale impacts of alternatives for managing the irrigated stream-aquifer system of the lower Valley, constrained by state water rights and interstate compact. The 'links and nodes' of the MODSIM flow and water allocation simulation model were successfully integrated in 2005 into a geographic information system format within the model. This allows storage reservoirs, river diversions, in-stream gaging stations, etc. to be displayed and accessed from a map of the lower Arkansas River. |
| 2006 | Water table depth and salinity were routinely measured in about 102 monitoring wells in the Upstream Study Region in the vicinity of La Junta, Colorado and in about 110 wells in the Downstream Region near Lamar, Colorado. Water table elevations were higher in 2006, indicating greater recharge to the water table from increased irrigation water applications and rainfall compared to the previous few years of drought. Surface-water salinity was routinely measured at numerous locations in the Upstream and Downstream Study Regions, including 8 locations in the Arkansas River upstream and 6 locations in river downstream. Data are still being processed and analyzed. Soil water salinity was measured late in the irrigation season on 12 fields in the upstream area and on 15 fields in the downstream area in 2006 for use in evaluating the impact of soil salinity on crop evapotranspiration (ET), estimated using satellite images of the fields. Results indicate a strong relationship between increasing salt concentration and decreasing ET. About 61 monitoring wells and 22 surface water locations (including six along the river) were sampled seven times during 2006 for dissolved selenium (Se) in the downstream area. Also, one sampling event for dissolved Se was conducted in 44 wells and 12 surface points in the upstream area. Analysis of downstream data collected from April 2003 until August 2006 revealed a median Se concentration of 16.6 micrograms/liter in groundwater. Se concentrations measured in the river ranged from 4.2 to 23 micrograms/liter with median of 10.2 micrograms/liter, exceeding the Colorado standard. Median Se concentrations in groundwater and in the river were 22.8 micrograms/liter and 4.5 micrograms/liter, respectively, upstream. Mass balance calculations were performed to estimate nonpoint source salt and Se loading rates to the Arkansas River for sample periods extending from 2000 to 2005. Tests were conducted on three canals to evaluate the effectiveness of polyacrylamide (PAM) for reducing seepage losses. Results were promising, indicating reductions of 38%, 59%, and 87%, within the first month of PAM application on three reaches that had substantial seepage. Work on refinement and calibration of the model of ground water flow for the Upstream Study Region continued. The enhanced model is first being calibrated for the period April 1999 - October 2001 and will be applied to simulate baseline and improved management strategies for the period April 1999 - October 2004. Work began toward calibration of the model for the downstream region to simulate flow, salt transport, and Se transport. Much progress was made in continued development and testing of GeoDSS, a spatial decision support model for predicting basin-scale impacts of alternatives for managing the irrigated stream-aquifer system of the lower Valley, constrained by state water rights and interstate compact. The model has been calibrated for flows and salt concentration for a historic period. The model predicts and displays flow and salt concentrations of reservoir releases, river diversions, and in-stream flows in a geographic information system (GIS) format. |
| Impact | |
| 1999 | Data collection efforts and modeling tools for characterizing salinization and waterlogging in the lower Arkansas River Valley in Colorado are helping guide the search for answers. Solutions must be based on accurate knowledge of field conditions to insure preservation of agriculture and rural communities in the Valley. Through systematic computational analysis, this project will evaluate and rank alternative solution approaches and publish specific recommendations. |
| 2000 | This project strengthens the data foundation and modeling tools for characterizing salinization and waterlogging problems in the lower Arkansas river valley and guiding the search for answers. Without sound and timely intervention, the Valley will succumb to effects of salinization. Through systematic computational analysis, the project will evaluate alternative solution approaches and publish specific recommendations. |
| 2001 | This project proposes to strengthen the data foundation and the modeling tools needed to characterize salinization and waterlogging problems in the lower Arkansas river valley and to guide the search for answers. Without sound and timely intervention, it appears that the Valley will eventually succumb, at least in a large part, to the ill effects of these problems . Solutions based upon accurate knowledge of field conditions will be needed to insure sustainability of the Valley's productive agricultural base and preservation of its rural communities. Through systematic computational analysis, the project will evaluate and rank alternative solution approaches and will publish a report making preliminary recommendations. |
| 2002 | This project strengthens the data foundation and the modeling tools needed to characterize salinization, waterlogging, and pollutant loading problems in the lower Arkansas River valley and to guide the search for answers. Solution alternatives considered thus far show promise both for boosting agricultural productivity on the land and enhancing the environmental health of the river. Results from the upstream study subregion suggest that strategies to reduce recharge to the water table by improving irrigation efficiency and reducing canal seepage would (a) lower the saline high water table leading to lower soil salinity and increased crop yields, (b) significantly reduce loading of salts and other pollutants to the river, and (c) markedly reduce nonbeneficial consumptive use under fallow land. This proposition will be verified and refined by data-calibrated subregional and basin-scale modeling. |
| 2003 | This project strengthens the data foundation and the modeling tools needed to characterize salinization, waterlogging, and pollutant loading problems in the lower Arkansas River valley and to guide the search for answers. Solution alternatives considered thus far show promise both for boosting agricultural productivity on the land and enhancing the environmental health of the river. Results from the upstream study region suggest that a variety of strategies are available that could (a) lower the saline high water table leading to lower soil salinity and increased crop yields, (b) significantly reduce loading of salts and other pollutants to the river, and (c) possibly reduce nonbeneficial consumptive use under fallow land. This proposition will be verified and refined by data-calibrated regional and basin-scale modeling. |
| 2004 | This project strengthens the data foundation and the modeling tools needed to characterize salinization, waterlogging, and pollutant loading problems in the lower Arkansas River valley and to guide the search for answers. Solution alternatives considered thus far show promise both for boosting agricultural productivity on the land and enhancing the environmental health of the river. Results from the upstream study region suggest that a variety of strategies are available that could (a) lower the saline high water table leading to lower soil salinity and increased crop yields, (b) significantly reduce loading of salts and other pollutants to the river, and (c) possibly reduce nonbeneficial consumptive use under fallow land. This proposition will be verified and refined by data-calibrated regional and basin-scale modeling. |
| 2005 | This project strengthens the data foundation and the modeling tools needed to characterize water conservation, salinization, waterlogging, and pollutant loading problems in the lower Arkansas River Valley and to guide the search for answers. The expanding database is enhancing our understanding of the nature, extent, and severity of problems related to water availability and use, salinity, and selenium pollution. Solution alternatives considered thus far show promise for boosting agricultural productivity on the land, saving water, and enhancing the environmental health of the river. Results to date suggest that a variety of strategies are available that could (a) lower the saline high water table leading to lower soil salinity and increased crop yields, (b) significantly reduce loading of salts and other pollutants to the river, and (c) possibly reduce nonbeneficial consumptive use under fallow land. This proposition will be verified and refined by additional data-calibrated regional and basin-scale modeling. Advances in the development of a basin-scale spatial decision support model indicate that alternative water management options along the river will be able to be explored in terms of their impact on the timing, magnitude, quality, and spatial distribution of in-stream flows, diversions, and state-line flows. |
| 2006 | This project strengthens the data foundation and the modeling tools needed to characterize water conservation, salinization, waterlogging, and pollutant loading problems in the lower Arkansas River Valley and to guide the search for answers. The expanding database is enhancing our understanding of the nature, extent, and severity of problems related to water availability and use, salinity, and selenium pollution. Solution alternatives considered thus far show promise for boosting agricultural productivity on the land, saving water, and enhancing the environmental health of the river. Results to date suggest that a variety of strategies are available that could (a) lower the saline high water table leading to lower soil salinity and increased crop yields, (b) significantly reduce loading of salts and other pollutants to the river, and (c) possibly reduce nonbeneficial consumptive use under fallow land. This proposition will be verified and refined by additional data-calibrated regional and basin-scale modeling. Advances in the development of a basin-scale spatial decision support model indicate that alternative water management options along the river will be able to be explored in terms of their impact on the timing, magnitude, quality, and spatial distribution of in-stream flows, diversions, and state-line flows. |
| Publications | |
| 2000 |
Burkhalter, J. P., Gates, T. K., and Labadie, J. W. 2000. "Model and field studies to manage saline shallow water tables in the Lower Arkansas Valley, Colorado." Proceedings of the International Conference on Irrigation and Drainage in the New Millenium, USCID, Fort Collins, Colo. |
| 2001 |
Gates, T. K., Burkhalter, J. P., Labadie, J. W., Valliant, J. C., and Broner, I. 2002. "Monitoring and modeling flow and salt transport in a salinity-threatened irrigated valley". Journal of Irrigation and Drainage Engineering, ASCE, 128(2): In Press. |
| 2002 |
Gates, T. K., Burkhalter, J. P., Labadie, J. W., Valliant, J. C., and Broner, I. 2002. "Monitoring and modeling flow and salt transport in a salinity-threatened irrigated valley". Journal of Irrigation and Drainage Engineering, ASCE, 128(2): 87-99. |
| 2005 |
Burkhalter, J. P., and Gates, T. K. 2005. Agroecological impacts from salinization and waterlogging in an irrigated river valley. Journal of Irrigation and Drainage Engineering, ASCE, 131(2): 197 - 209. |
| 2006 |
Burkhalter, J. P., and Gates, T. K. 2006. "Evaluating regional solutions to salinization and waterlogging in an irrigated river valley." Journal of Irrigation and Drainage Engineering, ASCE, 132(1):21-30. Wittler, J. M., Cardon, G. E., Gates, T. K., Cooper, C. A., and Sutherland, P. L. 2006. "Calibration of electromagnetic induction for regional assessment of soil water salinity in an irrigated valley". Journal of Irrigation and Drainage Engineering, ASCE, 132(5):436-444. |