Severn River Action Plan

Published: October 16, 2024

SRA Publishes the Severn River Action Plan

READ the Full Report

READ the Summary Report

SRA is proud to announce the publication of the Severn River Action Plan (SRAP): Subwatershed Planning Strategy and Weems Creek Subwatershed Action Plan. This is a long-term planning strategy for the Severn River Watershed that will help SRA better understand and track the status of subwatersheds and project implementation in the watershed. Additionally, this strategy builds capacity in the Severn River Watershed (Figure 1) to implement future on-the-ground water quality and habitat restoration activities. 

The SRAP was developed with technical assistance from the Center for Watershed Protection and support from a Steering Committee of key watershed stakeholders, including the City of Annapolis, and Anne Arundel County representatives. SRA is committed to using this plan to guide future project efforts. 

The SRAP is made of two parts. Part 1 is a strategic, phased approach to watershed planning based on a prioritization ranking of all the subwatersheds. Part 2 is the Weems Creek Subwatershed Action Plan, which presents a prioritized list of potential restoration projects in Weems Creek, the #1 priority subwatershed. 

Figure 1. Map of the Severn River with ranked subwatersheds

Part 1: Subwatershed Prioritization and Ranking

This section develops a strategy for long-term action planning by prioritizing and ranking all 108 subwatersheds of the Severn River watershed. It identifies priorities for restoration considering three major factors and their subcategories (Figure 2):

  • The need for restoration 
      1. Habitat 
      2. Biology
      3. Water Quality
      4. Total Nitrogen Loading
      5. Total Phosphorus Loading
      6. Total Suspended Sediment Loading
  • The need for planning
      1. Existing Watershed Plans
      2. Age of Existing Watershed Plans
      3. Current Restoration Status
  • Community support for restoration
    1. Presence of Community Support
    2. Environmental Justice Score

Figure 2. Weighting factors for prioritization 

More details about the data collected, how they were scaled and weighted, and the calculations of prioritization rank for each of the 108 subwatersheds are included in the full report. When everything was said and done a Prioritization Score (of a possible 1 to 100) and Prioritization Rank (1 to 108) was calculated for each subwatershed. The higher the Prioritization Score and lower the Prioritization Rank, the greater the priority (Figure 3). 

The #1 priority subwatershed is Weems Creek, which had a Prioritization Score of 72.1 and a Prioritization Rank of 1. 

Figure 3. Prioritization Score (colors) and Prioritization Rank (numbers) for each subwatershed. Subwatersheds with greatest need for restoration have a high Prioritization Score (red) and low Prioritization Rank (1 to 10). Weems Creek is the #1 priority subwatershed for restoration, as it has a Prioritization Score of 72.1 and a Prioritization Rank of 1. 

The long-term strategy is to update or develop action plans for each subwatershed in order of their Prioritization Rank while concurrently designing, permitting, and constructing the projects identified in them. Each subwatershed action plan may take five to ten years to implement most of the projects, assuming that sufficient and timely funding is secured. Factors that may make this take longer include delays in funding, permitting, and/or negotiations with landowners to implement these projects on their property.  Ultimately, implementing the projects identified is the actual key to realizing a thriving Severn River with improved water quality. 

Part 2: Weems Creek Action Plan

Weems Creek Subwatershed is the #1 priority subwatershed for restoration. It is 2.2 square miles and is heavily developed, with about half of its land in the City of Annapolis and about half in Anne Arundel County (Figure 4). About 42.4% of the subwatershed is impervious surface of some kind (e.g. roof, road, sidewalk, driveway or parking lot, etc., Figure 5). About 24% of the subwatershed is “Tree Canopy over Turf Grass” and 10% is “Turf Grass”. Both are mainly residential lots. So combined, 76% of the watershed substantially contributes stormwater runoff pollution (nitrogen, phosphorus and sediments) to Weems Creek. For perspective, aquatic ecosystems are negatively impacted by stormwater runoff pollution when >10% of the watershed is developed with impervious cover and/or turf grass. 

Figure 4. Map of 2017/2018 land use in and around Weems Creek subwatershed.

Figure 5. Map of impervious cover in Weems Creek subwatershed (yellow). 

To start identifying places for potential restoration projects, we first needed to identify what Best Management Practices (BMPs) already exist and then identify areas that are not already treated by these BMPs. Within Weems Creek subwatershed, there are ~148 existing BMPs in the City of Annapolis and ~238 in Anne Arundel County (Figure 6). These existing BMPs represent a wide variety of practices that treat nitrogen, phosphorus and sediments, as well as other pollutants. Nevertheless, there are large swaths of the Weems Creek subwatershed where stormwater runoff is not currently treated by a BMP of some kind (pink in Figure 7).  

Figure 6. Existing Best Management Practices in the Weems Creek subwatershed.

Figure 7. Areas of impervious cover that are not currently treated by BMPS are shown in pink. The remainder of impervious cover (yellow) is already treated in some way.

After further desktop and satellite analysis, specific sites within the areas not already treated were identified for field assessment to determine the feasibility of installing a new BMP or updating an existing BMP to extend its treatment area (Figure 8). The Center for Watershed Protection visited 37 sites, and of these, 18 were deemed suitable for retrofits. Sites were rejected as infeasible based on topography, land use, space constraints, or other reasons that would make constructing a stormwater retrofit too difficult or expensive.  

Most of the retrofit opportunities proposed are bioretention practices (Figure 9). Additional retrofit opportunities identified include two bioswales (Sites 10D and 20A) and opportunities for impervious disconnection and rain barrels. Sites 17A and 19A propose modifying existing site conditions or practices that would provide additional pollutant removal. Collectively, 1.26 additional acres of the Weems Creek subwatershed would be treated if all retrofit opportunities were implemented and ~1.08 acres of the impervious surface cover would be treated. Once implemented they would cumulatively remove an estimated 0.55 lbs/year of nitrogen,  61.66 lbs/year of phosphorus, and 6,011.7 lbs/year of sediment. 

Figure 9. Map of proposed projects from the field assessment.

Each of the proposed restoration projects is ranked based on eight criteria:

  1. Total nitrogen removal cost-effectiveness ($/lb)
  2. Total phosphorus removal cost-effectiveness ($/lb)
  3. Total suspended solids removal cost-effectiveness ($/lb)
  4. Maintenance needs (very little, quarterly, weekly)
  5. Demonstration value
  6. Ease of implementation
  7. Land ownership
  8. Site constraints

SRA and Center for Watershed Protection held a Weems Creek Restoration Community Meeting in early May 2024 to collect input and feedback on the potential projects. From this meeting, the community came to a general consensus on the following projects:

  1. Stream restoration at Weems Creek headwaters (South Branch)
  2. BMP 10 – A suite of stormwater practices at the Annapolis Exchange
  3. BMP 21 – Two bioretention at the Capital One Bank on West St.
  4. BMP 36 – Bioretention at the WNAV radio station on Admiral Dr.
  5. BMP 33 – Impervious surface cover removal at West St. and Gibralter Ave.
  6. BMP 12 – Bioretention in Annapolis Plaza parking lot off Jennifer Rd.

Cost estimates for these and the other identified projects as well as potential grant funding sources are also provided in the full report.

Next Steps

Now  our Severn River Action Plan is complete, the next steps are to develop additional subwatershed action plans, in order of priority, and to design, permit, and build the restoration projects that are identified in each subwatershed action plan. 

This project was funded by: