Watershed Facts: Technical Background

St. Johns River Water Management District

St. Johns River Water Management District - floridaswater.com

In this section

Surface water quality

2011 Water quality status and trends report

2010 Water quality status and trends report

Technical background

Arc Hydro represents advancement in the field of geographic information system (GIS) specifically for water resources applications. GIS has been used at the District for many years, but the advancements offered by Arc Hydro implementation allowed staff to perform GIS functions that were previously not possible or that were much more difficult and time consuming to perform.

The map below contains selected features from the District’s Arc Hydro geodatabase. The legend to the right of the map includes the Arc Hydro network, Arc Hydro Polygon Feature Classes and HydroPoints. The Arc Hydro network is composed of HydroEdges and HydroJunctions. The HydroEdges are a hybrid feature class, composed of two types of lines that represent surface water flow: those that represent streams and rivers, which are linear in nature, and those that represent flow through lakes and wetlands, not usually represented as linear features. Thus, the HydroEdges establish the connectivity of features in the Arc Hydro network. The arrowheads on the HydroEdges indicate the primary direction of surface water flow, ignoring tidal influence along the coast. The HydroJunctions are points where significant features can be linked to the network. The network is essential to Arc Hydro, allowing scientists to easily determine upstream and downstream relationships of surface water-related features. The Arc Hydro Polygon Feature Classes are District Catchment and Water body. The catchments represent local drainage areas and the water bodies are lakes. HydroPoints are hydrologic points of interest and include such features as water quality monitoring points, engineering structures and springs.