Hydrological Response Units (HRUs) at a regional-scale for the SNEP region within Massachusetts and Rhode Island

I.  SNEP HRU Project Background
The Southeast New England Program (SNEP) region consists of watersheds in Massachusetts and Rhode Island that primarily drain into Narragansett Bay, Buzzards Bay, or Nantucket Sound. It encompasses all or portions of 134 municipalities many of which are highly developed. The region faces multiple water quality issues with stormwater being previously identified a major contributor. These maps have been generated for all 134 Municipalities including 81 subwatersheds in the SNEP region to provide organizations and municipalities a way to understand where significant stormwater pollution may be originating. For organizations or municipalities with GIS capabilities the data that created these maps is available as well.
II.  What are HRUs?
Hydrologic Response Units (HRUs) describe a landscape through unique combinations of land use and land cover (residential, commercial, forest, etc.), soil types (A, B, C, D), and additional characteristics such as slope, and impervious cover. These landscape characteristics, or HRUs, provide the building block to quantify stormwater pollutant loads (nitrogen, phosphorus, and total suspended solids (TSS)) originating from a given land area. The HRUs and nutrient pollutant loads in stormwater provides a baseline from which reduction targets can be created.
III.  How can HRUs be used?
These maps and their underlying data can provide critical information to municipalities, watershed organizations, EPA, and others to assess stormwater pollutant loads in SNEP watersheds. EPA expects that this information will facilitate further understanding of the distribution of stormwater pollutant load source areas throughout the watersheds. This information serves to advance a broader understanding of stormwater impacts and potential management options by the public and direct stakeholders. Consistent HRUs may help municipalities implement MS4 permitting requirements and facilitate stormwater management strategies, such as land use conversion, stormwater Control Measure (SCM) siting, and targeting areas for conservation. HRU mapping can identify best locations for SCMs and can be utilized with additional stormwater planning tools (such as EPA’s Opti-Tool) to develop a cost-effective stormwater management plan. By providing a consistent HRU map for the SNEP region, practitioners can focus their efforts on implementation of SCM strategies rather than mapping their landscape. Hotspot mapping is a tool that integrates the HRU analysis and stormwater runoff pollutant load outputs to indicate areas where pollutant loads are highest and areas that stormwater controls may be best implemented. The HRUs and pollutant loads can be overlayed with parcel analysis to determine which parcels have high loads/areas of large impervious cover. The parcel data can help towns prioritize their efforts by determining the properties with highest potential to reduce pollutant loads through stormwater controls. Similarly, it can help determine which properties have large stormwater pollutant loads. 
IV.  Other Resources
HRUs That have been completed by EPA - Taunton River Watershed FDC Project and Tisbury, MA IC Disconnection Project 
The Cape Cod Commission developed HRUs for Barnstable County (CCC: Barnstable County HRUs).
The UNH Stormwater Center developed parcel level hotspot mapping in New Hampshire for municipalities to prioritize where new BMPs should be placed (UNHSC: NH Hotspot Mapping).

Tags: 020:085, contaminant, environment, land, massachusetts, rhode island, water
Organization: U.S. Environmental Protection Agency