Ground-water interaction with
surface water is a natural phenomenon dictated by the fact that the
two water media are critical components of one system that some
workers in this field have described as a three-dimensional
watershed. Ground water contribution to surface water can be in the
form of base flow to rivers and streams, submerged springs or
seepage of ground water into coastal zones. The USGS has estimated
the average of ground water contribution to surface water in the US
to be over 40% (Ground Water and Surface Water- A Single
Resource, USGS Circular 1139, 1998).
In another study; the USGS also estimated the percentage of
ground water contribution to selected streams across the country. The
estimates reflected a wide range of percentages of contribution as
illustrated in Figure 1 (Source: USGS Circular 1139, 1998) below. In
carbonate aquifers, such as the Floridan Aquifer System in north Florida,
conduit flow during the dry season can produce up to 100% base flow in
rivers such as the Suwannee. The implications of this interaction on
watershed health and on environmental regulation and protection can not be
over-emphasized. Unfortunately, the data needed to quantify such
interaction, which is necessary for implementing environmental protection
programs, has historically been both difficult and costly to obtain using
traditional hydrogeological procedures. This situation may have forced
workers in the field but to frequently ignore the fact of interaction and
deal with ground and surface water as two separate entities; to the
detriment of watershed and ecosystem health and integrity.
To help rectify this situation, the Hydrogeology Section at
FGS Hydrogeology Section has directed a significant amount of its
research effort to the development and field-testing of innovative
approaches to understanding the dynamics of SW/GW interaction. That in
turn, will help in providing better estimates of the sources and
quantities of water involved and in determining its quality. This
information is needed to model the flow of water and to predict the
behavior and fate of contaminants in karstic settings. In these settings
characterized by conduit flow and multi-porosity, the traditional flow
equations (Darcy’s Law) are not applicable, necessitating the
development of new models. It is our hope that once these new models are
proven effective in the field, they might be used by the regulatory
programs and the consulting community to account for ground-water
contribution while implementing various environmental programs. Possible
examples of such programs include Wetland and Source Water Management
and Protection, Waste-Load Allocation including springshed nutrient
loading, delineation of springshed boundaries and relative recharge
areas, public drinking-water supply well fields and calculation of Total
Maximum Daily Loads (TMDL).
The list of projects below is meant to provide the reader
with an idea about the overall direction of this research at FGS. Among
other approaches, the research seeks to demonstrate the effectiveness of
remote-sensing techniques in locating areas of ground water discharge to
surface waters. Once such promising areas are identified on a large scale;
they can be further “ground-truthed” on a more focused scale, for the
purpose of determining the quality and volumes of water involved.
Recent and Ongoing SW/GW Research:
Simplified Method for Estimating Ground Water Discharge
to Surface Water for the purpose of Tatal Maximum Daily Loads (TMDL) Allocations
Ground-water tracing studies
More about Woodville Karst Plain
Standardizing springs nomenclature
- Conduct thermography and resistivity surveys to increase
knowledge of surface-water ground-water interactions; surveyed areas of interest
to TMDL studies such as the Ortega River, Escambia Bay, and Lake Barco
- Apply the Wakulla Spring system and the Woodville Karst
Plain watershed as a hydrogeological observatory in support of modeling of
ground-water flow and contaminant transport in karst terrains, under this task
several projects were initiated including the following:
- Application of radium and radon
isotope measurements to estimate the rates of ground-water discharge to
surface waters via submarine springs or diffuse flow along the coastal zone.
- Assess feasibility of using Landsat imagery to locate
offshore sources of potable water.
of thermography, resistivity, side-scan surveys and site investigations to
characterize offshore springs.
- Evaluate the effectiveness and resolution of several
geophysical techniques (micro-gravity, resistivity, cave radios etc in
determining the location and morphology of caves and conduits.
- Evaluate the use of foraminifera as indicators of
historical salinity changes and pollution in coastal waters.
For information regarding these projects, contact Dr.
Rodney DeHan, FDEP/FGS Hydrogeology Section Outsourcing Manager.