Sustainability

Sustainability generally means the development and use of ground water in a manner that can be maintained for the present and future time without causing unacceptable environmental, economic, social, or health consequences.  This is the definition stated in Louisiana Revised Statute 38:3097.2.11.

Sustainable Yields and Thresholds of Concern

Sustainable yield is that quantity of water that can be withdrawn on a continuing basis by reaching a system equilibrium without compromising the integrity of the aquifer or with respect to agreed upon criteria. (9)  Sustainable yield is a critical element in identifying and designing viable water supply alternatives.  With sustain-able yield defined and knowledge of total water demand in an area, an unmet demand can be calculated.

Sparta-Louisiana Sustainable Yield

‘The Sparta Groundwater Study’ Results

The Sparta Commission contracted Meyer, Meyer, LeCroix and Hixson, Inc. to determine limitations of the Sparta to meet current and future needs and to test hypothetical conservation approaches.  The researchers entered well water level data, pumpage data, and information about Sparta’s hydrogeologic properties into a groundwater flow model,  USGS-developed (MODFLOW) software.  The study area was the Sparta aquifer in north central Louisiana and southeast Arkansas.  Predictions covered the time period 2000 to 2025.  The resulting ‘sustained maximum pumpage rate’ of 52 mgd was predicted to result in recovery, not to a pre-pumping state, but to a state of self-renewable stable supply, assuming the Sparta’s natural recharge and leakage rates continue close to historic rates. (2, ) 

The results of the study in 2001 were published in the Sparta Groundwater Study (2):

• The maximum recommended pumpage from the Sparta is approximately 52 million gallons per day (mgd).
• To achieve a pumpage rate of 52 mgd, pumpage must be reduced by 18 mgd, from the current pumpage rate of approximately 70 mgd.
• Decreased pumping must occur across the extent of the entire Sparta region for widespread effect.
• Developing alternative sources to produce an additional 12 mgd of potable water would provide for future increases in demand for potable water.

USGS Study by KcKee, Clark, and Czarnecki

Figure 26 depicts actual and optimal withdrawal rates estimated by an optimization study by McKee, Clark, and Czarnecki. (8)  Components of the optimization study, including the researchers’ definition of ‘optimal withdrawal’, and their data sources, estimations, assumptions, and methods, are reported in a publication of study results (8) and a publication describing project development (9)

The researchers note that estimates of sustainable yield are affected by 1) hydraulic-head constraints (the most important factor), and 2) the distribution of managed wells.  In terms of hydraulic head constraints, the researchers used for sustainable yield estimates the Arkansas ‘critical groundwater area’ criterion—water levels above the top of the aquifer.  They noted that lowering the hydraulic-head constraint in Louisiana, Louisiana having no established criteria for maintaining hydraulic heads above the top of the Sparta Sand, would increase the amount of estimated sustainable yield for both Arkansas and Louisiana.  Non-linear model behavior precluded reliable quantification of the increase.  In terms of well distribution, the researchers used the distribution of existing wells in the Sparta aquifer.  More strategic well placement might increase the sustainable yield estimates.