2 USCID/EWRI Conference

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3 Water Quality of Surface Irrigation Returns in Southern Idaho Clarence W. Robison 1 Richard G. Allen 2 Richard Merkle 3 ABSTRACT The Clean Water Act and Safe Drinking Water Act and the Environmental Protection Agency of the United States Federal Government have provided means and encouragement to irrigation projects and entities to improve the quality of surface water returns flowing to river systems. In Idaho, state and federal partnerships have set maximum concentration limits for suspended sediment (52 mg/l) and phosphorus (0.1 mg/l) on portions of the Snake River system and its tributaries through the total maximum daily load process. The irrigation community has responded by implementing programs and partnerships for improving quality of returning water. These programs include education, water quality improvement facilities and best management practices, and monitoring. BACKGROUND The Snake River reach between Milner and King Hill in southern Idaho is locally referred to as the Middle Snake River. Water quality in the 94-mile reach has been impacted various ways resulting in some of the designated beneficial uses not being attained within the reach (Figure 1). This stretch of the Snake River is impacted by return flows from irrigated agriculture, fish hatchery effluent, hydroelectric development, sewer treatment plant discharge, spring flows, grazing and recreational activities. The Middle Snake River often is referred to as a working river because of its highly regulated stream flow. Reservoirs upstream of Milner have a combined storage capacity in excess of 4.5 million acre-feet 4. Impoundments and diversions, 1 Clarence W. Robison, P.E., Research Associate, Department of Biological and Agricultural Engineering, University of Idaho, Kimberly, Idaho, USA 2 Richard G. Allen, Ph.D., P.E., Research Professor, Department of Civil and Department of Biological and Agricultural Engineering, University of Idaho, Kimberly, Idaho, USA. 3 Richard I. Merkle, Research Technician, Department of Biological and Agricultural Engineering, University of Idaho, Kimberly, Idaho, USA 4 Kjelstrom, L. C., 1995, Streamflow gains and losses in the Snake River and ground-water budgets for the Snake River Plain, Idaho and eastern Oregon: U.S. Geological Survey Professional Paper 1408-C. 243

4 244 USCID/EWRI Conference primarily for irrigation and hydroelectric power generation, have resulted in smaller stream flows and stream flow velocities thus limiting the Middle Snake River s ability to assimilate sediment and nutrient inputs from non-point and point sources. Figure 1. Map showing general location and area of interest. Water quality in the Middle Snake River reach is impacted by a variety of non-point and point sources of pollution. Non-point sources account for most of the sediment reaching the river and its tributaries. Primary non-point sources of pollutants are agricultural activities, animal grazing and irrigation. Primary point sources of pollutants in the reach are municipal wastewater-treatment facilities and aquaculture related activities. The degraded water quality in the river results from a combination of excessive nitrogen, phosphorus, pesticides, and sediment; and the cumulative effects of decades of non-point and point source activities. Excessive aquatic vegetation, low dissolved oxygen, and high water temperatures prevent water in this reach from meeting State water-quality criteria 5. Geologic and Hydrologic Setting The Middle Snake River flows through an incised canyon in the basalts of the Snake River Group. The present location and configuration of the river is the result of ancient canyon filling processes and erosion and deposition during the Pleistocene Bonneville flood. Flowing west of Milner Dam, the river becomes 5, 1997, The Middle Snake River Watershed Management Plan, Phase 1 TMDL, Total Phosphorus. Idaho Division of Environmental Quality, Twin Falls Regional Office, Twin Falls, Idaho.

5 Water Quality Monitoring of Surface Irrigation Returns in Southern Idaho245 incised in the basalts, and the elevation of the river drops below the ground water table elevation of the aquifers bordering the river. The primary outflow from the Eastern Snake Plain Aquifer occurs along the north side of the river. Springs issuing from the canyon walls contribute significantly to the river flow for the lower three fourths of the reach. These spring inflows contribute approximately 5,000 to 6,000 cfs to the river. Depending on the water supply in the Upper Snake River Basin, the flow entering the reach or passing Milner Dam may be as low as 200 cfs or as great as 30,000 cfs during floods. To meet storage and irrigation diversions upstream of Milner Dam the U. S. Bureau of Reclamation and Idaho Water District Number 1 control the flow passing Milner Dam and entering the reach. Adjacent to the canyon, 360,000 acres are surface irrigated with sprinkler and traditional gravity methods using water diverted from the Snake River above Milner Dam. The Northside Canal Company operates the diversion and delivery system on the north side of the river for 160,000 acres and the Twin Falls Canal Company operates the diversion and delivery system on the south side of the river for 200,000 acres. The majority of the farms are sprinkler irrigated on the north side (90%) compared to the majority of farms under furrow irrigation on the south side (75%). The crops include alfalfa, dry beans, corn, small grains, sugar beets, and potatoes. The soils are loessal in origin varying between 6 to 40 inches in depth. Most of the soils are classified as a silt-loam or sandy-loam and are highly erosive. The climate is considered semi-arid with most of the precipitation occurring during the winter and spring months. Irrigation return flow from the two systems enters the Snake River directly, from numerous surface drains on both sides of the canyon and tributaries, and indirectly through springs along the river and tributaries. These drains represent surface return flows from irrigated agricultural ranging from individual fields to irrigation canal company lateral returns. Excluding the individual field and farm drains, the canal companies estimate maximum surface return flows at approximate 420 cfs for both the north and south sides. Individually, the return flow drains typically have highly variable flows reflecting daily and seasonal patterns in water use. Water Quality Awareness In the early 1990 s, local citizens and concerned agencies formed a working group to address water quality problems within the Middle Snake River reach. As an outgrowth of the working group s activities, the State of Idaho implemented the nutrient management planning process. The working group served as the basis for the initial planning group. Representatives from the various industries, municipalities, irrigated agriculture, recreational and environmental groups served on the planning committee. The parties took a proactive stance on improving water quality in the reach. Many of the participants, including agriculture, developed proactive plans of action to reduce their impact on water quality in the

6 246 USCID/EWRI Conference reach and a few started implementing their plans. As the nutrient manage planning process was transformed into a Total Maximum Daily Load (TMDL) determination and allocation process overseen by Idaho Department of Environmental Quality (IDEQ) and U.S. Environmental Protection Agency (EPA), the planning group became in part the Mid-Snake Watershed Advisory Group. As a result of the efforts during the 1990 s, two TMDLs were written by IDEQ and approved by EPA for the Middle Snake River and it s associated tributaries. The first TMDL addressed total phosphorus within the Middle Snake River and set a target concentration of mg/l. Irrigated agriculture commitment to the first TMDL was to reduce suspended sediment entering the river via surface returns by 27 percent. Irrigated agriculture representatives and advisory staff felt that there would be an associated 10 percent reduction in total phosphorus by attaining the suspended sediment goal. Based on the commitment by irrigated agriculture, sixteen indicator drains were assigned specific phosphorus load targets. The second TMDL 6 addressed then entire Middle Snake watershed formally known as the Upper Snake/Rock Watershed. This TMDL set suspended sediment concentration target level at a mean monthly 52 mg/l with a daily maximum of 80 mg/l for the river and it s tributaries. Additionally, total phosphorus target concentration of 0.1 mg/l was set for tributaries. The analysis was based on the assumption that the quantity of return flow would not change. Canal Company Actions Over the past decade both canal companies have pursued a vigorous proactive course with regard to water quality in the Middle Snake River. The canal companies were instrumental in the formation of the Irrigators Water Quality Committee (IWQC). This committee was comprised of representatives from canal companies, local soil conservation districts, local farmers, the University of Idaho, the USDA Agricultural Research Service, the USDA Natural Resources Conservation Service and IDEQ. The committee served to guide the irrigated agriculture representatives on the various advisory groups associated with watershed management plans and total maximum daily load determinations for the Middle Snake River and its watershed. The committee also served as a clearinghouse on activities by the various entities on their efforts to improve water quality. The committee was instrumental in developing the irrigated agriculture management plan identified in the two Middle Snake River TMDLs. The committee additionally served in an oversight role for an irrigation return flow 6 Buhidar, Balthasar B., et al., 1999, The Upper Snake Rock Watershed Management Plan, The Upper Snake Rock Subbasin Assessment and The Upper Snake Rock Total Maximum Daily Load, Idaho Division of Environmental Quality, Twin Falls Regional Office, Twin Falls, Idaho.

7 Water Quality Monitoring of Surface Irrigation Returns in Southern Idaho247 water quality project funded by the two canal companies and operated by the University of Idaho. The canal companies have been diligent in efforts to build water quality improvement facilities on the various lateral returns and or drains prior to their discharge into the Snake River or its tributaries. The facilities are typically largescale sediment ponds and have retention times on the order of 4 to 36 hours. Some of the facilities have constructed wetland components. The partnerships developed by the canal companies to construct and operate these facilities have included: The Nature Conservancy, Idaho Power, Idaho Department of Fish and Game, and others besides local property owners. WATER QUALITY PROJECT The water quality project funded by the canal companies and operated by the University of Idaho received support from the U.S. Bureau of Reclamation who provided assistance in laboratory analyses. The project s approach identified by the canal companies, the university and the IWQC consisted of three key elements: education, water quality practices, and monitoring. The three components were intended to increase the project s potential for successfully improving irrigated agriculture s impact on water quality in the Mid Snake watershed. Education The education program focused on education and training on three levels: irrigators (landowners and operators), general public, and canal company staff. The two major goals of the education program were: (1) to bring about improved water quality in the Mid-Snake by emphasizing improved tillage and water management practices on the land; and, (2) to educate the general public about good-faith efforts underway by the canal companies and irrigators to improve water quality of irrigation return flows. The educational effort associated with farm owners, operators, and irrigators had two primary focus points. The first was to increase the awareness that irrigated agriculture along with other industries and municipalities does impact water quality in the Middle Snake River. The other focus of the irrigator education program was to provide information about the water quality situation and information on new technology and management practices for improving water quality in irrigation return flows. Proposed, enacted and adopted regulatory requirements regarding irrigation return flow water quality was provided to irrigators and landowners. Procedures were emphasized for management of delivery systems for sediment and nutrient control, on-farm tillage and irrigation management practices, and operation of sediment ponds and vegetative areas for both water quality improvement and wildlife habitat enhancement.

8 248 USCID/EWRI Conference The public education program provided a historical perspective of water development in Magic Valley and associated benefits, and an understanding of the irrigation process and it s impact on sediment and nutrient loading to the river. The operation of irrigation systems, constraints to change, and trade-offs in water management, energy, and water supply were presented to various public service groups, schools, and other organizations. Water quality improvements efforts by the canal companies and shareholders (landowners) were identified at those presentations and addition to various tours conducted for interested parties and regulatory agencies. Additionally, presentations were made to educate the agriculture support sector (consultants, business leaders, and lenders) on activities and practices that control erosion and reduce sediment and associated nutrients from surface return flows at the farm level. The educational effort associated with canal company ditch riders focused on water management, recognizing farmers and irrigators with successful water quality management plans, and identifying those who may need help. The hope was that the ditch rider would be able to discuss water quality practices with individual irrigators and farmers when the opportunity arose. They would be able to relay information needed or identify sources of help to those needing assistance. Information sessions on how canal company activities impact water quality within the canal system and finally the Middle Snake River were developed and presented to the employees. By increasing the water quality awareness of the canal company staff, opportunities for improving water quality by changing day-to-day operations and minor system changes were identified by the staff, some of which were implemented. Water Quality Improvement Facilities and Best Management Practices A majority of the farm level best management practices (BMPs) have centered on controlling erosion on the field and treating the surface runoff. These practices have changed little over the past years. They include modifying traditional crop management and water management practices. New BMPs have incorporated usage of chemical additives such as polyacrylamides to stabilize the soil structure. The historical control and treatment practices effectiveness has been documented in previous studies by various agencies. The effectiveness of new practices are being evaluated by the USDA Agricultural Research Service and others. University personnel provided assistance to the canal companies in locating potential water quality improvement facility sites, designing the facilities, and evaluation of alternatives. After implementing several facilities, the canal companies developed expertise in locating sites and facility design. The university monitoring program documented the performance of typical facilities on a caseby-case basis.

9 Water Quality Monitoring of Surface Irrigation Returns in Southern Idaho249 WATER QUALITY MONITORING The water quality monitoring program developed by the University of Idaho for irrigated agriculture consisted of four components: attitudes, best management practice and facility performance, surface return flow quality, and in-stream water quality of the Middle Snake River. The first two components were to assess the effectiveness of the educational program and implemented practices. The remaining components of the monitoring program were to assess water quality trends and improvements related to the Mid Snake and irrigation return flows. Attitudes An attitude survey was developed by University of Idaho Extension staff and mailed to irrigators within each canal company service area. The attitude survey attempted to quantify the impact of the educational program of the project. Surveys were mailed to all canal company shareholders irrigating more than 5 acres. The surveys were conducted four times during an eight-year period. The survey was not a rigorous survey where similar statements were repeated in different forms. From the results of the four surveys, the attitude of the irrigation community appeared to have changed. Initially, the owners and operators were of the opinion that sediment control practices either cost too much, required too much time, or reduced yields. By the last survey the respondents had moderated their opinions. The level of agreement to statements in the survey expressing that practices took too many resources changed from agreement to disagreement. Based on the surveys and the educational efforts, the canal companies were able to adopt bylaws governing the quality of surface water returning to the distribution and return flow systems. The stockholders (landowners) of the two companies have supported management s allocation of more resources to water quality programs within each company. Water Quality Improvement Facility Monitoring While the irrigated agriculture nutrient management plan identified best management practice implementation on the irrigated fields, the irrigation companies have constructed water quality facilities on the drainage systems. The typical facility is a sediment pond; however, constructed wetlands have been built in cooperation with landowners and conservation groups. Components from a constructed wetland concept have been implemented where applicable. The monitoring program addressed the need for facility monitoring to document performance. In-stream Monitoring The in-stream water quality-monitoring program was based on the monitoring work performed by the University of Idaho on the Middle Snake River

10 250 USCID/EWRI Conference for the IDEQ 7. Four selected locations along the Snake River were monitored on a biweekly schedule. The monitoring locations along the reach were Milner Dam (inflow), Blue Lakes Bridge (Twin Falls), Clear Lakes Bridge (Buhl), and Shoestring Bridge (Bliss). The monitoring package consisted of field parameters and laboratory parameters. The parameter list included air and water temperature, dissolved oxygen, ph, electrical conductivity, transparency, total suspended solids (sediment), ammonia nitrogen, nitrate nitrogen, total Kjeldahl nitrogen, dissolved orthophosphate, total phosphorus, and chlorophyll-a. These four monitoring sites were to provide trends on water quality in the river and provide a data set for evaluating the success of all efforts, not only irrigated agriculture, in improving water quality. Over the decade of monitoring, the discharges in the Middle Snake River ranged from historical lows to historical highs. Figure 2 shows the average daily discharge for the Snake River at the USGS station near Kimberly for the period of monitoring. Snake River near Kimberly Discharge (ft 3 /sec) 1000 Jan1989 Jan1990 Jan1991 Jan1992 Jan1993 Jan1994 Jan1995 Jan1996 Jan1997 Jan1998 Jan1999 Jan2000 Jan2001 Figure 2. Snake River daily discharge near Kimberly, ID. The wide variation in flows over the decade has resulted in difficulty in determining trends in suspended sediment loads within the reach. During the early 1990 s, the region experienced a drought with very low flows. Sediment was being deposited in various areas of the river. These deposits along with deposited sediment from irrigation return flows during the twentieth century were eroded during the high flows in 1996 and later years. Figure 3 shows average quarterly suspended solids loads in the river at Blue Lakes Bridge near Twin Falls. These 7 Brockway, Charles E. and Clarence W Robison, Middle Snake River Water Quality Study, Phase I, Idaho Water Resources Research Institute, University of Idaho, Moscow, Idaho

11 Water Quality Monitoring of Surface Irrigation Returns in Southern Idaho251 loads are based on the bi-weekly monitoring results and represent between six and seven measurements. Clearly, there does not seem to be a trend in the loading at the site not associated with stream flow. Snake River at Blue Lakes Suspended Solids Load (tons per day) C 1990D 1991A 1991B 1991C 1992C 1992D 1993A 1993B 1993C 1993D 1994A 1994B 1994C 1994D 1995A 1995B 1995C 1995D 1996A 1996B 1996C 1996D 1997A 1997B 1997C 1997D 1998A 1998B 1998C 1998D 1999A 1999B 1999C 1999D 2000A 2000B 2000C Return Flow Monitoring Figure 3. Quarterly Suspended Solids Load near Twin Falls The surface return flow-monitoring program focused on 16 irrigation return flow drains discharging directing to the Middle Snake River reach. The drains were identified by the IDEQ and the University of Idaho in a study as contributing over 60 percent of the irrigation return flow volume to the river. The drains were identified in the first TMDL developed for the Middle Snake River as the key indicator drains for irrigated agriculture and had individual phosphorus loads allocated to them. The program targeted these drains to be monitored on a biweekly basis every three years for temperature, dissolved oxygen, electrical conductivity, flow, total suspended solids (sediment), ammonia nitrogen, nitrate nitrogen, total Kjeldahl nitrogen, dissolved orthophosphate, and total phosphorus. On the off years, some of the drains were monitored for total suspended solids and total phosphorus. Figures 4 and 5 show the concentrations over time of suspended solids and total phosphorus for a typical southside irrigation return flow drain. This drain is showing improvement from the various activities on its watershed (farmland) over the past decade. A web site has been created and maintained to make the collected water quality data available to the public ( The site contains summary data for the various parameters at each monitoring site along with scatter plots of the data over time.

12 252 USCID/EWRI Conference Southside Irrigation Return 1000 Suspended Solids (mg/l) / 1/1990 1/ 1/1991 1/ 1/1992 1/ 1/19931/ 1/1994 1/ 1/1995 1/ 1/1996 1/ 1/1997 1/ 1/1998 1/ 1/1999 1/ 1/2000 1/ 1/20011/ 1/2002 Figure 4. Suspended solids concentration for a southside drain. 1.5 Southside Irrigation Return Total Phosphorus (mg/l)",ylog= / 1/1990 1/ 1/1991 1/ 1/1992 1/ 1/1993 1/ 1/1994 1/ 1/1995 1/ 1/1996 1/ 1/1997 1/ 1/1998 1/ 1/1999 1/ 1/2000 1/ 1/2001 1/ 1/2002 Figure 5. Total phosphorus concentrations for a southside drain. SUMMARY AND CONCLUSIONS Water quality monitoring of irrigation return flows has provided valuable information on magnitudes of and trends in the quality of surface waters returning to the Snake River of southern Idaho. Data show a general improvement in return flow quality resulting from adoption of best management practices and proactive water management programs by local canal companies. The water quality of the mid Snake River should also improve over the near future as surface returns improve and as other programs supported by the TMDL process evolve.