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About ISGW
Simulating both surface water and groundwater and their interaction in one hydrologic model remained a dream for many years. Surface water models moved water into a groundwater zone, usually never to interact with surface water again. Groundwater models added stream-aquifer interactions, but did not simulate the rainfall-runoff component of stream flow. Thus, neither model could be used effectively for long-term predictive simulations where the interactions between surface water and groundwater are important.
Why do we need an integrated model?People have come to realize that groundwater pumping can cause reductions in stream flow and lower water levels in lakes and wetlands, affecting the ecology and wildlife of an area and reducing water available for senior water rights. SDI co- developed an integrated hydrologic model in Florida designed to predict hydrologic conditions in reclaimed wetlands after phosphate mining. Recognizing the value of the integrated hydrologic model for assessing regional water resource development, SDI continues to expand the capabilities of the integrated hydrologic model. ISGW, SDI's integrated surface and groundwater model, is the result of that effort.
What can ISGW do?
By coupling the strengths of the surface water model HSPF with the strengths of the groundwater flow model MODFLOW, and allowing water to transfer between each model, ISGW simulates the major hydrologic processes, including
The secret of the integration is letting each model component do what it does best, exchanging necessary information between components. The result is a model that is capable of completing hydrologic simulations lasting up to several decades.
Yes, if you want to avoid repeating mistakes and further harming the environment. Interactions between surface water and groundwater can be slow, taking months or years for impacts to be observable, particularly in wetlands. SDI has successfully applied ISGW to sites ranging in size from 50 acres to nearly 4,000 square miles. Recent applications of ISGW focus on the development of new water resources while minimizing impacts to the environment. Nearly 500 million gallons of groundwater and surface water are withdrawn daily to serve the growing needs of west-central Florida, and ISGW has successfully simulated the long-term (1971- 1998) hydrologic responses caused by these stresses. One client has incorporated ISGW into a regional operations plan to optimize production from more than 170 groundwater wells.
Show me the money!
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Good model results are cheaper than poorly designed facilities. How good are the results from ISGW? The comparison between observed and simulated stream flows is best illustrated by the accompanying flow-duration graph. Both low and high monthly average daily flow patterns are well represented by ISGW. A comparison of observed and simulated groundwater levels illustrates how well ISGW represents the groundwater component of the hydrologic cycle. Observed seasonal fluctuations and longer-term fluctuations due to above- and below-average rainfall and due to changes in groundwater pumping are accurately simulated by ISGW.
Are integrated hydrologic models the wave of the future?
We at SDI believe so. The advantages are many, while the disadvantages of additional cost and complexity are diminishing each day as our understanding of the integrated hydrologic system improves along with computer hardware and software. Don't be fooled by numerous "pseudo-integrated" hydrologic models reported in the literature. Very few truly integrate the surface water and the groundwater systems as ISGW does.
Please contact SDI if you are interested in learning more about the possible application of ISGW to your problem.     
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