Description: Basins: Local level basins are the largest drainage unit tracked by Tallahassee-Leon County government and reflect final destinations of surface water drainage. Lake Jackson is, for example, a natural lake where a substantial amount of surface water runoff ultimately collects. Ames Sink (Lake Munson Basin) is a natural swallet (a sinkhole where surface water enters the aquifer) where surface watercourses terminate into the Floridan Aquifer. Lake Miccosukee is a water feature in part created from infrastructure that controls water elevation (weir/spillway) and a berm that prevents the surface water from draining into the aquifer by way of a swallet.
Description: Watersheds: Watersheds are groups of catchments aggregated (merged) to produce even larger more meaningful drainage units. The results are produced from storm-water inventory wherever possible and indicate where water ultimately collects. This could be a much larger storm-water facility, a natural area (lake or depression) or other area where a greater volume of surface water collects.
Description: Catchments: Catchments are an aggregated set of data. Meaning groups of sub-basins (deranged areas) are merged to create larger more meaningful boundary areas. For natural areas this could be several shallow depressions being included with a larger nearby natural feature (lake, sink, etc.). Meaning depending upon rainfall conditions an entire area of interconnected lower elevation depressions coalesce into a larger drainage area. For developed areas, this could mean a series inlets direct surface drainage by way of conduits to a storm-water management facility. This information is processed by either known inventory data connection or by best assumption.
Description: Sub-Basins: The sub-basin data is identical geometry to the ‘deranged area’ boundaries produced by Archydro, an extension of ESRI ArcGIS software. The deranged area boundaries used to produce the sub-basins are themselves produced by hydro-correcting the DEM surface to reflect both natural environments and areas with human activity. Areas with more substantial human activity effect the drainage pattern of water and in particular storm-water runoff. This would include things like paved roads, paved parking lots and buildings. An effort has been made to produce deranged area boundaries at locations where storm-water runoff is directed (inlets, grates, storm-water ponds, etc.) and as well natural locations in the environment (sinks, depressions, confluences, etc.). Hydro-correcting involves a certain amount of modification and manipulation of the DEM surface to produce better results. For example, ‘burning’ in a channelized ditch along a road with many driveway aprons that obscure the subsurface ditch (driveway culverts) beneath. A deranged area boundary is created by leveling an area that approximates where the water would flow (inlet, pond, sinkhole, etc.) by way of gravity and infrastructure that directs it (ditches, curbs, etc.). From the leveled area the ArcHydro software uses the DEM to generate the drainage boundary (deranged area boundary) using the DEM surface.