Hooffs Run Watershed - Characteristics and Features.

 

 

Hooffs Run Watershed - Characteristics and Features.

Storm water and Sewers: 

As outlined on the City of Alexandria website, the city operates two types of storm sewer systems: A separate sewer system and a combined sewer system (CSS). The separate system consists of two pipes (one each for sewer and storm water), where as the CSS combines sewer and storm water in a single pipe. During moderate to heavy rain, the pipe can become overloaded with storm water and raw sewage may overflow in to local streams (including the Hooffs Run Stream/Tributary). 

The Hooffs Run watershed encompasses both systems, although the majority of the watershed surface area is serviced by the separate system. The Hooffs Run stream, seen in the map below, holds significance as it is the site of two CSS Combined Sewer Overflow (CSO) Stations (red dots 003 and 004). A detailed GIS Sewer Viewer maintained by the City of Alexandria displays how storm water and sewage are collected in old town, then channeled towards the Hoofs Run Stream. 

Source: River Renew CSS Annual Report for 2019

 

Source: virginiaplaces.org

 A report on the CSS by the City of Alexandria notes, “The Outfall 004 regulator consists of a weir and slightly elevated outflow pipe in series. When flow becomes so large that it overtops the weir and the water surface is high enough to reach the invert of the overflow pipe, it is discharged into Hooffs Run.” 

The CSS is subject to a significant infrastructure project designed to reduce these overflows, which will involve a network of tunnels and sewers connecting to a treatment plant. Detailed information on the CSO, including number of annual overflow events and average volume of overflow, can be found through this link to virginiaplaces.org. 

Beyond this significant project, the City of Alexandria conducted a ‘Green Infrastructure Technology Evaluation’ to identify alternatives for CSO control (i.e. to reduce the amount of sewage and storm water in the Hooffs Run Stream). The following Green Infrastructure (GI) technologies were analyzed during the study: permeable pavement, planter boxes, bioswales, rain garden and downspout disconnects. However, in relation to CSO-003 and 004, it was concluded these GI alternatives are more suited as a complementary technology, and on their own will not achieve the required bacteria reduction (seen when sewage and storm water pass through the outfall regulator). 

Geographic features 

The western side of the Hooffs Run watershed is bordered by hills that rise up from the suburb of Del Ray and small portion of the southern tip of Old Town. The base of these hills largely run north/south parallel with Russell Road, rising to a height of approximately 150 feet. 

On the eastern side of the watershed, the mapped boundary concludes short of Highway 1 (apart from a small section on the western most tip), but covers the entire Metrorail (and Amtrack) section from King Street to Braddock road station.  

Source: USGS ScienceBase Catalog 

Perhaps the most easily recognizable landmark within the Hooffs Run watershed is the George Washington Masonic National Memorial. The memorial stands atop Shuters Hill at an elevation of approximately 100 feet on an irregular parcel bounded by King Street to the north, Duke Street to the west and south, and Callahan Drive to the east (Virginia Department of Historic Resources). Shuters Hill is a registered archaeological site, with findings suggesting the location was inhabited by native Americans for over 5000 years (i.e as early as 3000 BCE) .   

Geology 

The Hooffs Run Watershed spans three distanced types of bedrock, as outlined in this geological survey conducted by the City of Alexandria. The elevated areas of the watershed are largely part of the ‘Sykesville Formation and early Ordovician (OCs)’, with most of Del Ray part of the ‘Rock Creek Shear Zone (RCSZ)’, then the southern part (including Hoofs Run stream) part of the ‘Chopawamsic Formation (Oc)’. According to the survey, the various rock units are part of the mid-Atlantic Piedmont which occupies the area between the Blue Ridge Mountains and the Atlantic Coastal Plain. They were formed about 450 to 550 million years ago.