Dr. Robert Knight has written an article in the Gainesville Sun, April 24, 2016, explaining the vast differences between what the water managers want to believe and the truth regarding ground water withdrawals.
Robert Knight: Flawed models used to permit groundwater pumping
By Robert Knight
Special to The Sun
Published: Friday, April 22, 2016 at 6:01 a.m.
Last Modified: Wednesday, April 20, 2016 at 2:41 p.m.
The fate of Florida’s groundwater resources rests on the accuracy of mathematical models. Scientists and engineers estimate groundwater flows and levels by collecting and summarizing data from wells, rivers and springs. They then use computers to simultaneously solve thousands of equations to give the best fit between actual and modeled groundwater levels and spring and river flows.
Problems arise when the conceptual aquifer structure does not match reality and when computer-generated parameters are not constrained by real aquifer characteristics. The result is that groundwater models often include significant discrepancies between actual and predicted levels and flows.
The Florida Springs Institute enlists highly qualified technical advisors to provide independent review of the models used by the state to manage groundwater resources. Those experts have concerns about the poor quality of the models used for evaluation, review and issuance of water-use permits by the water management districts (WMDs) throughout Florida.
Based on information provided by the WMDs, it is apparent that many of the existing groundwater flow models have not been thoroughly reviewed, validated or used with adequate caution. Without proper review, water managers and the public cannot have confidence in the results provided by the use of these models.
Complex models need to be thoroughly reviewed by competent professionals with no vested interest in the outcome of the reviews. Scientific peer review comments need to be addressed with appropriate modifications. The Florida Springs Institute recommends that each model be reviewed by at least two independent peer reviewers, followed by full public disclosure of review comments and documentation of how the models are revised to effectively incorporate suggested improvements.
It is imperative that the accuracy of every groundwater-flow model used for allocating groundwater pumping permits be estimated and reported along with model predictions. Many of the models prepared for water-use permitting are intended for regional analysis and yet they are applied to site-specific permitting applications. Gross over-estimates of groundwater availability appears to be the norm. Model estimates of spring flow reductions due to groundwater extractions are strikingly different from actual measured changes in spring flows.
For example, the St. Johns River WMD’s best models estimate that Silver Springs flow has been reduced by about 5 percent by groundwater pumping while actual average flow reductions are greater than 30 percent. The Southwest Florida WMD’s groundwater model estimated that pumping lowered flows at the Gum Slough Springs Group by 3 percent while actual data show a 50 percent spring flow decline. And the Suwannee River WMD’s model predicts an average decline in Ichetucknee River flows of 5-9 percent while an independent analysis by the U.S. Geological Survey documented a 23 percent decrease.
The degree to which modelling errors impact efforts to protect springs was most clearly revealed two years ago after independent experts reviewed the model used by the St. Johns River WMD to establish minimum flows and levels for Silver Springs. The model initially indicated pumping had such a negligible effect on Silver Spring’s flow that additional groundwater withdrawal permits could be issued before significant spring impacts occurred.
After an outside review, the WMD admitted that flows at Silver Springs were already more than 12 million gallons per day past the point of significant harm. Efforts to address that impact are still underway. The salient point is that the state’s model was drastically wrong, and if not for independent review, the error might not have been caught.
A more recent groundwater modeling effort was initiated by the state in 2014 to better assess the cross-boundary effects of massive groundwater withdrawals in northeast Florida and southeast Georgia. This model, named the North Florida Southeast Georgia model, includes the same flawed framework as the previous WMD groundwater flow models.
These models all include the assumption that the Floridan Aquifer does not include caves and large underground conduits, a conceptual error that leads to unreasonable aquifer characteristics contradicted by actual data. It is not reasonable to expect a measurable improvement in the accuracy of groundwater pumping impact estimates provided by this new and “improved” North Florida Southeast Georgia model.
On behalf of all Florida citizens who wish to have a sustainable groundwater future, Florida Springs Institute advocates for a full and truly independent review of that model before it is adopted for issuing the next round of groundwater permits. The public cannot tolerate another inaccurate and unbelievable conclusion that additional groundwater withdrawals will have no impact on our dying springs and lakes.
— Robert Knight is director of the Howard T. Odum Florida Springs Institute in High Springs