[4] Models are available for individual components of the hydrological system such as surface runoff;[5] there also exist basin wide models addressing hydrologic transport and for ocean and estuarine applications.
Often finite difference methods are used to analyze these phenomena, and, almost always, large complex computer models are required.
A SPARROW model is a SPAtially-Referenced Regression on Watershed attributes, which helps integrate water quality data with landscape information.
[2] More specifically the USGS used this model to display long-term changes within watersheds to further explain in-stream water measurement in relation to upstream sources, water quality, and watershed properties.
[2] A SPARROW model used by the USGS focused on the nutrients in the Nation's major rivers and estuaries; this model helped create a better understanding of where nutrients come from, where they are transported to while in the water bodies, and where they end up (reservoirs, other estuaries, etc.).