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By Dr. Eric Flaig and Dr. Sanjay Shukla 1.0 INTRODUCTION Agriculture in the Caloosahatchee watershed depends on water released from Lake Okeechobee for supplemental irrigation. If runoff is more effectively stored within the watershed, and existing or planned reservoirs can adequately retain and release a large portion of that water, then growers will likely gain an additional management tool for on-farm water management. At the same time, growers will substantially decrease reliance on water from Lake Okeechobee. The South Florida Water Management District (District) has set guidelines for the construction of wet detention basins for the impoundment of agricultural drainage water before it can be discharged off site. An effort is made to include and connect existing wet areas when locating and sizing a wet detention area. Exterior dikes are located and sized to allow passage of off-site flow while protecting the grove area. Interior lateral and collection ditches are located, sized and installed to provide drainage. These wet detention basins for drainage water from citrus groves have four primary functions (Pitts, 1989): 1) maintain off-site discharge peak flows at or below pre-development levels; 2) provide detention time for sediment removal and enhancement of the quality of discharged water; 3) preserve wetland habitat; and 4) provide groundwater recharge areas. Groundwater recharge is likely occurring from the wet detention basins. Much of the soil in the region has a semi-permeable organic hard pan at a depth of about 1meter that limits downward percolation. The canal created to provide fill for the dike construction usually penetrates the pan. However, it is likely that with time, recharge rates will diminish as sedimentation occurs. Although it is commonly believed that above-grade retention/detention facilities are not effective storage reservoirs, there is little information confirming that effective reservoirs cannot be constructed. This project is designed to determine the potential effectiveness of surface water reservoirs for storing water for supplemental irrigation. The storage, seepage, ET losses, and hydroperiod characteristics of local water storage opportunities should be carefully and rigorously evaluated. However, this project is not intended to prioritize alternative storage strategies for the Caloosahatchee Water Management Plan. The University of Florida, Institute of Food and Agricultural Services (University) shall be responsible for conducting the study and reporting on the activities set forth herein. 2.0 SCOPE OF WORK The scope of work consists of five tasks designed to develop necessary information concerning reservoirs for water storage in the Caloosahatchee Watershed. The individual tasks are presented and discussed in Section 3 of this document. The tasks cover a number of activities that include:
The results of the work shall be presented in two workshops, one workshop presented to the growers and one workshop for the US Army Corps Of Engineers and the District. 3.0 WORK BREAK-DOWN STRUCTURE Task 1. Field Monitoring – Installation of Equipment. The parties will mutually select three reservoirs for detailed evaluation. The evaluation shall consist of a detailed water budget for each reservoir documenting evapotranspiration and seepage losses, including monitoring water levels inside and outside of each reservoir, and monitoring weather data and pumpage. Observation wells shall be installed to determine the piezometric gradients. The following equipment, supplied by the District, shall be installed at each reservoir: 1) weather station, 2) pump monitoring instruments, 3) surface water and groundwater level monitoring equipment. Task 2. Survey of reservoirs. The current retention/detention facilities shall be evaluated to determine the effectiveness of those facilities for enhanced water supply management. The survey shall include a review of water use and surface water permit files and field visits where possible. The area of available retention in the watershed shall be evaluated. The University shall create a table of key characteristics for each reservoir that affect water retention. The University shall interpret the results obtained from the field measurements in relation to the watershed. The data shall be used to determine seepage behavior of the reservoir for different antecedent conditions. The fill materials of the dike, bottom, and sides of each reservoir shall be measured for hydraulic conductivity, particle-size distribution, and potential seepage rates. Task 3. Reservoir models A preliminary model shall be developed to evaluate the impact of distributed reservoirs on water storage in the Caloosahatchee Watershed. The model shall evaluate the potential storage based on daily values of evapotranspiration developed using the AFSIRS model. The University shall estimate the change in supplemental water requirement and runoff for selected crop and soil types using the model. The model shall utilize a 31-year period of record of daily data. Field studies shall be conducted at each reservoir site to develop site-specific data for the model. These studies shall include land survey, vegetation survey, and well tests to determine hydraulic conductivity. The University shall develop a reservoir simulation model to determine the water budgets for each reservoir. The model shall be used to calculate evapotranspiration based on weather data, seepage, and pumpage. The model shall be used to assess uncertainty in the field measurements. A coupled groundwater/surface water simulation model shall be developed for each reservoir. Each model shall use an entire farm as the simulation domain and the Caloosahatchee Watershed model (a MikeSHE model) to obtain boundary conditions. The model shall be used to test parameter coefficients for the Caloosahatchee Watershed model. Task 4. Evaluation of Alternatives The University shall evaluate alternative water management strategies for each of the three, instrumented reservoirs. The objective of the alternatives shall be to improve the availability of water supply to a farm. The evaluation of alternative strategies shall be constrained by practicable solutions and management that is consistent with wildlife values. Where possible the University shall field test alternative methods to improve water retention capabilities of the reservoirs. The evaluation of alternatives shall include development of a criteria matrix that indicates the conditions suitable for reservoir construction. The suitability analysis shall include thematic maps indicating the suitability for reservoir construction in the Caloosahatchee Watershed. This analysis shall also include guidelines for construction of new reservoirs. The University shall develop two workshops for dissemination of the information collected during this study. The first workshop will be presented to the growers at part of the University of Florida Extension Service to inform growers about the management of farm reservoirs for meeting water supply The University shall develop information that shall aid the District in preparing the Caloosahatchee Water Management Plan addressing the use of reservoirs for agricultural water supply. The results of this project shall be address the issues identified by the CWMP Advisory Committee. Task 5. Project Completion and Documentation Data collected after the interim reporting period shall be analyzed and incorporated into a final study report by the University. The data shall also be used to further refine the model. Results of the model refinement and application, and documentation of the workshops shall also be included in the report. A summary of the study and recommendation of future work will be provided. The final report shall contain the following components: 1) results of the wet-season and dry season monitoring for the three reservoirs, 2) results of model application, 3) the evaluation of alternative management strategies based one complete year of field data, and 4) the results of the two workshops. 5.0 LOCATION OF THE PROJECT The project will be conducted within the Caloosahatchee Watershed. All laboratory and engineering analysis will be conducted at the Southwest Florida Research and Education Center (SWFREC) of the University of Florida in Immokalee. 6.0 PROJECT MANAGEMENT The principal investigator for this project on behalf of the University of Florida, IFAS is Dr. Tom Obreza. The District project manager is Dr. Eric Flaig who is assigned to work on-site at the SWFREC facility. 7.0 DISTRICT RESPONSIBILITIES The DISTRICT will supply the field equipment and materials necessary for monitoring the water budgets at the three reservoirs monitored in Task 1. This equipment is necessary for developing calibrated models in Task 3. The District project coordinator, Dr. Eric Flaig who is assigned to the SWFREC, will be directly involved technically in all aspects of this work order including development of any intellectual property. The District will provide timely review of any documents to be submitted. Additional review time will extend the due dates of future deliverables. 8.0 CONFIDENTIALITY All data information used in the preparation of the products for this work order will be subject to a thorough scientific or engineering review before use and release. No grower information will be published without review. No grower data will be collected that is not directly required to complete the products required in this work order. There are no known trade secrets required to complete the work products. |
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