The following is an email first published June 9, 2011, from Peter Schreuder, hydrological consultant for LAWA:
Attached are copies of two figures in the USGS Report 2011-5031 from a section of the report starting on page 160. This section is entitled: “Analysis of Long-Term Trends in Flow from a Large Spring Complex in Northern Florida”. The data shown graphically in Figures 1 and 2 contain important hydrogeological and groundwater resources in formation. In Figure 1 it shows that the second highest ground water elevations (potentiometric surface) in Northern Florida occur in the Keystone Heights area. In 1980 the elevation of the groundwater in the Floridan Aquifer was as high as 90 ft above mean sea-level also referred to as NGVD. This is indicating a very productive recharge area from the lakes into the underlying Floridan Aquifer. From the Keystone Height the ground water flowed southward and to the St John’s and Santa Fe rivers as indicated by the arrows.
In Figure 2 you can see that ground water withdrawals in Northeast Florida area apparently changed the direction of ground water flow away from the Suwannee River area and more towards the Duval County area. The effect extended all the way to the Keystone Heights area. It resulted in a lowering of the potentiometric surface by approximately 10 feet in the Keystone Heights area. One can conclude this by looking at the map which no longer shows a contour line for the 90 ft level.
Hydrogeologically speaking the data indicate that the Keystone Heights area, in particular the lakes in this area, is a central and important feature to provide replenishment of water to the Floridan Aquifer through recharge of surface water from the lakes into the underlying Floridan Aquifer. The more surface water we can bring to the lakes, the more recharge we can deliver to the ground water system and the better the Floridan Aquifer will regionally be.
Peter
Peter Schreuder, P.G.
Schreuder Inc
www.schreuderwater.us
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