Mattawoman Creek Watershed

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Characteristics

The Mattawoman Creek is a 60,300 acre watershed located in Prince George's and Charles Counties. Approximately 44,479 acres of the total area is located in Charles County. The Creek originates in Brandywine in Prince George's County and flows south towards Waldorf in Charles County, where it begins to followthe border between the two counties at U.S. Route 301 and goes to the Maryland Route 228 crossing.

From this point, it flows southwest about nine miles to Maryland Route 225 where it becomes a seven mile tidal estuary before entering the Potomac River. There are nine subwatersheds nested in the Charles County portion of the Mattawoman watershed, each averaging 7 square miles and defined by the Maryland Department of Natural Resources(MDNR) as 12 digit watersheds. Some of the major tributaries to Mattawoman Creek include Piney Branch, Old Woman's Run, Laurel Branch, and Marbury Run.

Several factors define the character of the watershed; some of these include the following:

Designation as an Area of Critical State Concern

The Mattawoman Creek and its tidal and non-tidal wetlands were identified in a 1981 Maryland Department of State Planning report on areas of Critical State Concern. The Creek, its wetlands and its tributaries are among the most productive finfish spawning and nursery streams in the entire Chesapeake Bay region.

The wetland areas support unusually large numbers of fish-eating wildlife, especially Great Blue Herons, Great Egrets, Bald Eagles, and Black-Crowned Night Herons. The tidal wetlands contain the native lotus plant, Nelumbo lutea. Otter, mink, osprey, and beaver, as well as the largest concentration of nesting Wood Duck in Maryland are found here.

Chemical and Biological Indicators

The 1998 Maryland Clean Water Action Plan rated all of the watersheds in Maryland for water quality, aquatic living resources, landscape parameters, and clean water requirements

In the water quality category, the Mattawoman was in the top 25% of all watersheds in Maryland for having the highest poundage of nitrogen and phosphorus in the watershed per watershed acre. These two nutrients are known to cause algae blooms which block sunlight to submerged aquatic vegetation(SAV). Nitrogen and phosphorus also consume large amounts of dissolved oxygen from the water that fish and plants need to survive. The creek exceeds two federal clean water quality requirements - - nutrients and sediments.

In the aquatic living resources category several measurements were poor, while several other measurements were good. For example, the acreage of SAV, which is mostly found at a water depth of six meters or less, is poor. Scores for number of fish species and trophic composition (food web composition) were also in the lowest 25%. Good scores in this category were for high numbers and diversity of aquatic species listed as rare, endangered, threatened or otherwise of special concern, high number of species of migratory fish that use the creek as a spawning area, and high numbers of ecologically valuable anadromous and semi-anadromous fish.

In the landscape parameters category the Mattawoman also rated poorly in some measurements and well in others. The Mattawoman scored well and exceeded State goals for a high percentage of headwater streams occurring in interior forest and high acreage of watershed forest and wildland. Parameters in which the Mattawoman rated poorly were high density population, large amount of historic wetland loss and a high soil erodibility indicator.

Land With Long Term Protection

In the Charles County portion of the watershed, there are approximately 5,900 acres of state protected land and park land and 316 acres of County park land. Additionally, Charles County holds Forest Conservation Easements on approximately 400 acres in the watershed.

Current Zoning and Demographic Trends

The majority of the Mattawoman Watershed is designated as a Development District in the 1997 Charles County Comprehensive Plan. The Development District is the principal center of population, services and employment in the County, and generally coincides with the Mattawoman Sewer Treatment planned sewer service area.

A portion of about 15,000 acres of the District is currently classified as a Deferred Development District. This area is not yet able to support higher densities of development because it is not connected to public water and sewer. The goal of the Comprehensive Plan is to encourage growth to emanate from the urban core and town centers, thus reserving the deferred development areas until the necessary public facilities are extended to serve these areas.

Recent census data show Charles County is the eighth fastest growing county in Maryland, with a 19.5% population increase from 1990-1999. This is probably due to the abundance of available land and the close proximity to the Washington, D.C. metropolitan area. According to the County's 1997 Comprehensive Plan, 70-75% of the new growth in Charles County will be directed to the Development District. If 70% of the new growth expected by 2020 does actually occur in the Development District, then the population in this area will increase by 49,666 people.

Impervious Surface and Build-Out

Potential

Impervious surface has been cited by several studies to have a relationship to the water quality of a watershed. Some of these studies include Klein(1979) "Urbanization and stream quality impairment," Schueler (1994) "The Importance of Imperviousness", Maxtec and Shaver(1996) "Watershed Protection using an integrated approach", and Horner, et al (1996) "Watershed Determinates of Ecosystem Functioning." The Rapid Watershed Planning Handbook, by the Center for Watershed Protection in Ellicott City, Maryland states that at over 10% impervious cover, watersheds show clear signs of degradation. These signs include erosion, channel widening, and a decline in biodiversity, with the most sensitive fish and aquatic insects disappearing from the streams. As calculated by Department of Natural Resources in 1999, two of the nine subwatersheds in the Mattawoman watershed have impervious surface percentages over 10%. These are the Piney Branch subwatershed, which includes most of St. Charles west of U.S. Route 301, and part of the tidal Mattawoman Creek Watershed, which includes the Town of Indian Head and the U.S. Naval Surface Warfare Center.

A 1996 issue paper prepared in conjunction with the County's update of the 1997 Comprehensive Plan, entitled "Protection of Environmental Resources within the Charles County Development District," estimates that at build-out of the Development District approximately 8,607 acres of the total 45,503 acres in the Development District will be impervious surface. This equals approximately 20 percent impervious surface cover when all properties are developed to their zoned capacity. This issue paper was done prior to the State's 1998 purchase of 2,225 acres, slated for the Chapman's Landing Community and turning it into a park, and the County's recent Deferred Development District zoning, where the residential density has been reduced from one dwelling unit per acre to one dwelling unit per ten acres.