Early Tenants Prove the Success of the Richmond Wetlands Project
Jefferson Village is the site of a major wetlands mitigation project located in the city of Richmond, VA, in an area containing significant residential, commercial, and industrial development. The project has provided several benefits to the community, including mitigation for wetland impacts, public recreation, research and education, wildlife refuge and habitat, and flood-flow attenuation.
Reedy Creek is a perennial stream that flows generally parallel and adjacent to Midlothian Turnpike, a major commercial roadway that passes through southwestern Richmond. While Reedy Creek has a relatively low constant water flow, it conveys substantial stormwater runoff from a 4.2-mi.2 urbanized area. The Reedy Creek watershed is contained within a 23-mi.2 area annexed by the city in the early 1970s. The creek ultimately discharges to the James River, also in southwestern Richmond.
Increased development and dense urbanization have negatively impacted this stream. It has degraded in areas, and existing drainage structures have been unable to convey even routine storm flows from frequent storms. Channel banks have eroded or collapsed in some areas, while undersized culverts and drainage structures have caused flooding in others. Flooding is a frequent occurrence in many areas along the stream, resulting in property damage and increased risks to human safety.
The City of Richmond began implementing an ongoing capital-improvement program in the early 1970s to improve the condition of Reedy Creek and its ability to convey the increased stormwater runoff from the developed watershed. Stream-channel improvements constructed in phases through the early 1990s consisted mostly of segments of concrete-lined channel sized to convey peak storm flows quickly downstream. While these measures were effective in reducing localized flooding, this approach did little to enhance water quality or reduce the scour effect of the high water velocities in the downstream reaches of Reedy Creek. It also led to significant wetland impacts.
The United States Army Corps of Engineers (ACE) and the Virginia Department of Environmental Quality (VDEC) developed wetland regulatory programs in the 1980s; as a result, the city was required to obtain permits from the agencies for any channel improvements to Reedy Creek. These permits included the requirement to construct a suitable wetland mitigation site. Phase XII was completed in 1992, and construction ceased until the city could locate and design a wetland mitigation site. ACE and VDEQ determined that approximately 2.8 ac. of immediate wetland mitigation would be required to proceed with Phase XIII. City officials and the agencies wanted the new wetland site to lie within the city and the Reedy Creek watershed, but since Richmond is highly developed, many people were concerned that acquisition and development of such a site would prove prohibitively expensive.
There were many challenges to finding a suitable site. The Reedy Creek watershed is located in one of the older, more urbanized areas in southwestern Richmond. Commercial, residential, and industrial developments line both sides of the stream channel, much of it constructed prior to modern flood-encroachment or stormwater management regulations. Few open areas remain in the watershed, and the economically depressed area recently has become a target for redevelopment initiatives. The topography within the Reedy Creek watershed is generally flat along the basin boundaries but slopes quickly toward the stream. In some areas, the channel is incised and eroded, making it difficult to divert or impound water without a lot of excavating. Many of the culvert crossings are undersized and several have undergone short-term repairs.
A major sanitary sewer interceptor ran along nearly the entire length of the stream and crossed it in numerous places. In addition, other utilities, such as water, gas, and electric, cross the stream in many places, with very few record drawings showing the location of these lines.
HDR Engineering Inc., under contract with the city’s Department of Public Works for stream improvements in the Reedy Creek watershed, initiated a search for potential mitigation sites within the watershed. Criteria for wetland site selection included:
- sufficient land to provide the required mitigation credit;
- avoiding relocation of businesses or residences and minimizing any private property takings;
- minimizing existing structure demolition;
- avoiding contaminated sites;
- minimizing impacts to natural resources, such as wetlands or endangered or threatened plants and animals;
- compatibility with adjacent lands;
- availability of lands for purchase or justification for condemnation, including economic feasibility;
- minimal excavation or earthwork needed for construction;
- existence of potential hydrologic sources;
- potential to create additional wetlands for anticipated impacts from future stream improvement projects.
In addition, sites were evaluated based on their proximity to the creek, adjacent land uses, soil types and conditions, topography, level of existing vegetation, tree-removal requirements, proximity to mapped floodplains, and utility conflicts.
After an initial desktop review of mapping and numerous field assessments, three potential sites were identified within the watershed. Two of the potential sites were larger undeveloped properties in the size range of 20-30 ac. They were located in lower areas of the watershed, and both had steep topography and contained dense tree stands of mature hardwoods. Since already-viable natural habitat would be destroyed to create a wetland, the likelihood of obtaining regulatory approval to permit these sites as mitigation areas was not promising.
The third identified site was located within the Jefferson Village apartments, an abandoned apartment area in the upper reaches of the watershed. It met most of the criteria set by the design team and offered some great opportunities to provide environmental and recreational benefits to the community.
The Jefferson Village apartments historically had been an area of crime and economic depression. The entire apartment property had been targeted for redevelopment and at the time was owned by the Richmond Redevelopment and Housing Authority (RRHA). A large portion of the site was being developed with the construction of approximately 40 single-family homes. In addition, RRHA had sold a large parcel of the site to the school board for construction of a much-needed elementary school. Engineers working with the city had already begun design of the new infrastructure for these facilities.
Reedy Creek extended through the northern corner of the property, and the water quality within that section of the stream was relatively poor. The opportunities for new development within this portion of the property were limited because of its presence within the 100-year floodplain. Soil conditions were suitable for wetland construction. While site topography would require some excavation, it appeared to be the most appropriate site from that standpoint. Hydrology did not appear to be a constraint because of the close proximity of the stream. Additionally, the relatively flat site required only limited clearing since most of it had previously been used as a swimming pool and clubhouse by the apartment complex.
Another deciding factor in favor of the Jefferson Village site was its presence in the upper reaches of the watershed. Only about 15% of the watershed’s 2,660 ac. drained to the site. This would reduce the potential for poor water quality in the stream and also minimize the potential for extremely high-velocity flows during routine storm events that were frequent in areas downstream.
Other deciding factors:
- Preliminary coordination and a site visit with the state and federal permitting authorities indicated that the site would be suitable and permitable.
- The site would be compatible with the redevelopment of the area as proposed by RRHA and the school board.
- The site would be acceptable to the surrounding homeowners because it was such a dramatic improvement to the previous eyesore that they had long sought to change.
- There were three potential sources of water: the stream, offsite drainage into the site, and groundwater inflow.
- The land already was in public ownership and would merely take an interagency transfer to acquire.
- An opportunity existed for the proposed wetland to become a community-enhancement feature for recreation, research, and education.
- A sanitary sewer interceptor ran adjacent to the stream but was located on the south side of the site where the topography was much higher.
- There were miscellaneous water, sewer-service, and power utilities on-site, but all were abandoned.
- A preliminary site assessment showed no evidence of contamination.
The city’s Department of Public Works was able to acquire the property, and planning and design of the mitigation site began immediately. Certain challenges were identified at this stage, including a desire to minimize excavation costs, avoid impacts to an existing sanitary sewer main, and avoid the perception that a wetland site in such close proximity to residential neighborhoods would be a “snake-infested mosquito trap.” The public relations component is a significant factor in all of the project activities under the Reedy Creek Public Improvements Program.
With the most suitable site selected, the engineering design met many challenges and opportunities to optimize the existing conditions and provide a site that not only supplied the required mitigation credit, but could also serve as a community asset. The southwestern section of the City of Richmond has limited green spaces or parklike areas. The potential for the site to also provide these types of community amenities was considered at an early stage.
A walking path was designed around the 4-ac. site, with an observation deck that extended into the wetlands. Two pedestrian bridges were added over the creek. These features were designed to enhance the aesthetic value of the site.
An additional feature included in the site design was a rock drop structure. With Reedy Creek flowing directly through the site, the designers wished to “flatten” the stream to reduce velocities and optimize the stream overflow into the adjacent wetland cells during storm events. This necessitated the installation of a rapid drop in the flow line at the downstream portion of the site with the appropriate energy dissipation. The drop structure was constructed of large-diameter riprap with larger boulders in the bottom to provide energy dissipation. The drop structure was placed immediately upstream of one of the pedestrian bridges to provide an aesthetic feature near the site’s pedestrian access.
Efforts were made during design to maximize the creation area but avoid impacts to existing perimeter trees. Additionally, great care was taken during construction to keep the contractor from impacting areas outside the project limits. The access path that extended around the perimeter of the site was routed to preserve certain forested areas near the channel at the upstream and downstream ends of the property. The planting phase will include upland trees and shrubs to improve the buffer between the creation site and the adjacent residential lots.
The design team placed considerable value in achieving an improvement in the condition of Reedy Creek within the site boundaries. Prior to the project, the section of Reedy Creek lying within the site limits was in very poor condition with limited vegetation. A deteriorated culvert and road crossing provided access across the creek, and substantial amounts of debris and trash had accumulated in the channel. The stream had very little buffer separating it from the adjacent parking lots and apartments. The wetland project provided an opportunity to dramatically improve the stream conditions.
The site required limited demolition of a swimming pool and an associated pool-house building. Demolition of these features was coordinated with the other site demolition performed by RRHA.
Excavation was considered the most critical factor affecting the ultimate project cost because of the site’s location in an urban area with no nearby permanent stockpile opportunities. The contractor would need to haul and dispose of nearly all of the excavated material. A small amount of material could be used for fill in certain areas of the site.
Based upon the suitability of the soils and the location of the stream, the first design approach was to bring the entire site down to stream level. Reedy Creek then would provide hydrology to all of the created wetlands within the site. This approach, however, led to a significant soil-removal requirement. A reduction in the amount of excavation could only be achieved by creating separate self-contained “cells” or terraces within the site at differing elevations. Cells at elevations significantly above the stream elevation would not be inundated under normal storm conditions. Therefore, other sources of hydrology were sought.
Direct runoff to the site from the adjacent properties was limited. It was estimated that fewer than 5 ac. of drainage area would discharge to the site under normal conditions. The search for a hydrologic source expanded to a roadside drainage swale approximately 500 ft. north of the site. At the time, this swale transmitted runoff from approximately 32 ac. of single-family residential land uses to Reedy Creek well upstream of the site. By regrading a connecting drainage swale to flow in the opposite direction, the runoff from this drainage area was rerouted to flow directly into the site. The drainage area was well within the guideline of providing approximately 10 ac. of drainage area per acre of created wetland.
The project team had concerns that flow velocities from the discharge pipe for this runoff could lead to instability within the site and/or damage vegetation. For this reason, a forebay was designed at the point at which the water entered the site, which would provide energy dissipation and sediment deposition. Based upon site observations since the completion of construction, it is anticipated that this separate forebay area will also be planted with wetland species.
With a hydrologic source secured, it was clear that hydrology could be provided to an upper cell. The second requirement would be to keep it there long enough to support wetland vegetation. The presence of the groundwater table was not included in the design considerations because of the uncertainty associated with predicting long-term water-table elevations. Studies indicated that while the site contained suitable soils to support wetland vegetation at the stream level, the subgrade in the upper cells would allow water to percolate more rapidly than was desired. For this reason, a low-permeability requirement of 2.6 x 10-6 cm/sec. for the upper cells of the site was developed. The contractor was required to meet the design permeability in the upper cells with city-directed confirmatory testing, and the city was to pay for all passing tests.
A permeability technical specification was prepared that allowed the contractor to achieve the goal in one of three ways: stockpiling onsite clays and marls for use as subgrade, importing and installing a clay liner, or augmenting the existing soils with granular bentonite. The contractors were given access to the city’s soil assessment reports and performed their own soil borings prior to submitting a bid. While this approach was challenging during the construction phase of the project, it resulted in constructed wetland cells that maintain significant levels of water, with an even lower permeability than the natural subgrade adjacent to the creek.
From the initiation of the project, there was a desire to create a wetland site that would be an amenity for the surrounding community. Pedestrian access is provided by two public-road rights of way at opposite ends of the property. Two cable gates restrict vehicular access. Since completion of construction, the walking trail extending around the perimeter has been used frequently by local residents. The city also plans to install park benches, picnic tables, and other improvements during the planting phase of the project to be conducted in the winter of 2000 and the spring of 2001.
Another major component of the city’s efforts to improve Reedy Creek has been coordinating the project activities with the public. The Reedy Creek watershed has a very active and interested community of citizens, including the Reedy Creek Coalition, the Friends of Forest Hill Park, and several city-sponsored neighborhood teams. The design team worked very closely with these groups and others in the community to gather input regarding the goals of the project and include them in its development. Coordination with these groups has continued, and citizen participation in the tree-planting effort is planned.
Since completion of construction, the site has seen a substantial increase in volunteer-emergent wetland species, especially in the portions of the site immediately adjacent to the stream. The upper cell also has seen substantial volunteer growth and has remained wet throughout the year. The efforts to control infiltration in the upper cell are proving to be successful. Significant populations of ducks, geese, and other migratory birds have visited the site, demonstrating that in the midst of urban development, it is possible to maintain an ecological balance.
The site is also emerging as an educational tool. Teachers at the nearby elementary school frequently take their classes to the site for environmental education, and local graduate students inquire about studying the site. It is also used by nearby residents for recreation and exercise and will provide an immediate benefit for the science curriculum at the newly constructed elementary school. It also has been the subject of water-quality sampling and analysis by middle and high school students at the Greater Richmond Area Health Education Center.
