Illinois Environmental Protection Agency

Bruce Rauner, Governor

To report
, call the
Illinois Emergency
Management Agency
(24 hrs/day)

Notice of Nondiscrimination
Notificacion Sobre Actos Discriminatorios
Inspector General

Agencies, Boards & Commissions

Illinois Legislature

Kidz Privacy

Targeted Watershed Contents

Delineation of Watersheds

The first step in the watershed prioritization process involved the delineation of watershed boundaries at an appropriate scale. Watersheds boundaries needed to be hydrologically defined, consistent with USGS eight-digit hydrologic unit codes, and based on a framework linked to version 3 of the USEPA river Reach File (RF) coverage. Using these general criteria, the USGS eight-digit hydrologic catalog units (51 in Illinois) were further sub-divided into smaller scale watersheds in a manner compatible with first version of the USEPA Reach File in 1987. At the same time, the Illinois EPA developed a statewide database for tracking designated use assessment information for Section 305(b) of the CWA (the Illinois Water Quality Report) called the State Water Body Tracking System (WBTS). A link was established between the Illinois EPA’s stream coding system and RF1. This link allowed WBTS designated use assessment data to be reach indexed to a RF1 level of detail, and increased Illinois EPA’s ability to target watersheds based on decisions that were data driven.

RF2 (the second version of the Reach File) maintained the integrity of RF1 and added one level of tributaries from the USGS Geographic Names Information System (GNIS). These additions were limited to streams of at least three miles in length and more than one-half mile from an existing RF1 intersection. RF2 doubled the number of stream miles found in RF1.

RF3 (the third version of the Reach File), maintained stream reach designations from earlier reach file versions, and incorporated USGS 1:100,000 scale Digital Line Graph (DLG) data into the Reach Files network configuration. This created an endpoint at every intersection, and included such geographic features as roads, map edges, and stream confluences. The level of detail added in RF3 made it a viable tool for Geographic Information Systems (GIS) applications.

In 1995, Illinois EPA utilized GIS technology to reach index the WBTS assessment data for 305(b) to a RF3 level of detail while simultaneously redelineating the 832 watershed boundaries (Figure 1) to a 1:24,000 scale. This allowed for an electronic link between the WBTS data and RF3, which greatly enhanced Illinois EPA’s ability to target watersheds based on data driven decisions.

Figure 1. Illinois EPA Delineated Watersheds

Water Menu

2012 Illinois Clean Water Initiative
Water Pollution Control
Public Water Supply
Financial Assistance
About the Bureau
Rules & Regulations
Partners for Conservation
Water Resource Assessments
Total Maximum Daily Load
Storm Water Requirements
Green Infrastructure Plan
Nutrient Issues
Harmful Algal Bloom and Algal Toxins
Copyright © 1996-2011 Illinois EPA Agency Site Map | Privacy Information | Kids Privacy | Web Accessibility | Agency Webmaster