GSS Partners on Clean Water Rule Spatial Analysis

In February of 2017, the Trump administration directed the Administrator of the Environmental Protection Agency (EPA)and the Assistant Secretary of the Army for Civil Works (Assistant Secretary) to revise the definition of Waters of the U.S. (WOTUS). The definition is used to determine which streams, rivers, lakes, coastlines and wetlands are protected from draining and filling under the Clean Water Act. Due to a combination of subsequent rule makings and court challenges, two definitions are currently used in the United States. There are 28 states where waters are defined by the 1986 definition of Waters of the U.S. in combination with guidance developed following the 2006 Rapanos Supreme Court decision and 22 states where waters are defined by the 2015 Clean Water Rule definition.

In December 2018, the EPA and Department of Army published another proposed rule with a new definition of WOTUS to replace both of these. The new proposed rule would remove many waters and wetlands from Clean Water Act protection that are currently protected by both the 2015 and 1986 definitions. There is a clear need for analytical materials, such as a digital map of different watersheds in the U.S. that shows which waters and wetlands are protected and which are not protected under these three scenarios. Such a resource could help elected officials, policy makers and the public understand what waters are currently protected, as well as the extent and impact of the changes proposed by the Trump Administration, so they can comment on the proposed rule and plan for potential future changes in the extent of waters protected under the Clean Water Act.

With grant funding from the Hewlett Foundation, GSS created a geospatial model that predicts the spatial extent of federally protected wetlands and waterways. This model uses three different analysis scenarios:

1. Most Restrictive Scenario - This scenario limits protection of wetlands to those directly adjacent to perennial (permanent) streams/rivers only.

2. Very Restrictive Scenario - This scenario limits protection of wetlands to those adjacent to protected perennial (permanent) and intermittent (seasonal) streams/rivers.

3. Less Restrictive Scenario - This is the least restrictive of the modeled scenarios and limits protection of wetlands to those adjacent to protected perennial, intermittent and ephemeral (temporary) streams, and ditched or channelized streams.

This comparative analysis was completed for three geographically diverse case study watersheds using GIS and publicly available geographic digital data. The methods and communication of results were guided by a project advisory committee made up of science and legal professionals. The results of the analyses in the case study watersheds show that narrowing the scope of federally protected waters would significantly reduce the number of streams, wetlands and wetland acreage protected by the Clean Water Act, leading to a potential loss of benefits provided by wetlands that would no longer be protected under the Act. These benefits include water quality protection, floodwater attenuation, fish habitat and wildlife habitat. The methods and results of this work can be found in the final report and in a story map developed with Esri technology.