Crawford,
if you have fluvial deposits on the creek bed, that extend out into the lake, then it suggests that your area is not down cutting, so you are less likely to find active vadose systems, more likely to find phreatic systems or no conduit flow at all.
You said that there has been a lowereing of the water table due to (farm/agricultural) use. I would look towards the wells, there is often good sources of information from those.
Well/bore drilling logs can tell you a lot about the water table and the geology near the surface. I would go and talk to the local guy with the drilling rig, see what he has to say. If he pulls out a couple of divining sticks, then drink his whiskey and take the whole thing with a grain of salt.
Another source of information about subterranian flow that can come from contamination and environmental impact studies. Look for any pig or dairy farms in the area and check out their "sediment" ponds. Often times these were sources of groundwater conbtamination and show up in local council environmental impact studies etc. E.Coli is a great tracer in karst areas, as soon as an outbreak of ecoli poisoning occurs, hydrological studies happen. The water tracing is relatively easy, and usually well documented.
From the topographical maps you have look for drainage polygons. Closed valleys are a great indication of conduit flow. If you have a relatively flat landscape like we have here, then this wont help much.
If the overlying clay is thick, then you might be out of luck, sediment rapidly fills up capilliary conduits, and decreases the recharge of agressive water, you might be stuck with just a throughflow aquifer.
Have you contacted the NSS? They may have someone in your area!