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Reduction of Effluent Discharge and Groundwater Use in Catfish Ponds – Field Validation : Reduction of Effluent Discharge and Groundwater Use in Catfish Ponds – Field Validation D.W. Rutherford, T.P. Cathcart, and J. Hargreaves Mississippi State University


Slide2 : Introduction About 10 years ago, Pote and Wax modeled a “drop – add” method to reduce ground water use and effluent release (the “6/3 scheme”). Projected reductions in water use and release averaged about 30 percent.


Slide3 : The next logical step was to consider deepening production ponds to increase rain water storage. Considerations: How to bring such a system online gradually as part of routine maintenance. How to allow producers to partly drain ponds when needed without throwing away stored water


Slide4 : Deepened Modified drainage A solution: When ponds are being reconstructed, deepen them to increase their water holding capacity and then allow adjacent ponds to drain into them instead of into a ditch.


During rainy periods, conventional production ponds would discharge to the production / storage ponds instead of to receiving waters. : During rainy periods, conventional production ponds would discharge to the production / storage ponds instead of to receiving waters.


Stored water would be used for filling production ponds for as long as the water was available. : Stored water would be used for filling production ponds for as long as the water was available.


This idea was modeled using a 26 year meteorological record. Two scenarios were modeled: : This idea was modeled using a 26 year meteorological record. Two scenarios were modeled:


Slide8 : Simulations using the model predicted: Up to 70 % reduction in effluent release and groundwater use (depending upon configuration and storage depth); Some years with no effluent release or groundwater use at all; In years when effluent release occurs, most will be during late fall, winter, and early spring (when dilution is greatest).


Slide9 : Effluent discharge and groundwater use have both become issues of concern in the catfish industry. Non-point source pollution has become a hot topic in all sectors, including agriculture. Producers would like to have additional water management options should the regulatory climate become more severe. Producers are also aware of their dependence on groundwater and want to be prepared for possible future restrictions.


Slide10 : With this in mind, a study to test this approach was funded in 1999 by the Southern Regional Aquaculture Center (USDA). The purpose of the study is to test the reliability of the model and determine whether there are unforeseen problems associated with the use of this approach. 7 one acre ponds at DREC are being used; The study has a 3 year duration (data collection began March, 2000).


Slide11 : To look for unforeseen consequences of this approach, we will monitored water quality and fish growth. The ponds have been stocked at commercial rates. Standard water quality analyses were conducted biweekly. The ponds were monitored as per standard practice.


Slide12 : Testing the model (1:1 and 3:1 configurations). We had to deepen 2 ponds. Production/storage pond being deepened and reworked.


Slide13 : New drains from adjacent ponds. New outflow Partially completed production/storage pond


Slide14 : A Deepened Pond 1.25 m depth Drain depth 60 cm of storage Pipe to flume


Slide15 : Pond modifications: We had to re-route the drainage (from production to production/storage ponds). We had to re-route the drainage out of production/storage ponds through the outflow measuring system.


Slide16 : To Flume Drain from adjacent pond


Slide17 : Measurements required for model inputs: Evaporation and precipitation data (already measured on site). Pond geometry (depth and surface area of catchment) – carefully surveyed before and after pond modifications.


Slide18 : Measurements required for model inputs: Pond depths (for infiltration estimates).


Slide19 : Model dependent variables to be measured: Volume of stored water and groundwater pumped into production control and production/storage ponds.


Slide20 : Dependent variables: Volume of water discharged from control and Production/storage ponds. Good picture of system – the one that’s printed


Slide21 : Dependent variables: Volume of discharge This is the hardest one. We’re using H flumes:


Slide22 : Dependent variables: Pressure transducers in still wells (used to compute volume flow rates):


Slide23 : Automated data collection:


Slide24 : Dependent variables: The systems were calibrated prior to installation


Slide25 : and then installed on site.


Slide26 : Data collection began mid-January, 2000. One CR-10 and 1 sensor have been damaged (lightning). Data collection appears to be progressing satisfactorily.


Slide27 : After a very dry January – February, the discharge measuring system was finally put to use in late March, early April.


Slide28 : System performance: The system performed Reliably for the 2 years that it has operated. This summer we will be working up most of the Data from the project. We have (rather hurriedly) assembled some results from the “6 / 3” control pond (results from Deepened ponds are not ready for viewing).


Slide29 : During the first 200 days of operation, there were approximately 50 days that rain occurred. Discharge from the 6 / 3 pond occurred on 4 days.


Slide30 : Treating the 2 consecutive days of rain as 1 “event”, you can see how the available storage reduced effluent release.


Slide31 : 3/20: 808 ft3, 0.22 acre-in 4/2: 19,862 ft3, 5.47 acre-in 4/3: 2,706 ft3, 0.75 acre-in 5/5: 2,447 ft3, 0.67 acre-in Effluent release:


Slide32 : Model Validation (only 3 points so far): Predicted vs Observed