V: WATERSHED PLANNING WATERSHED V: Restoration and preservation policies for rivers, streams, tributaries, and wetlands begin with an identification of the existing conditions as issues and opportunities within watersheds, culminating in the development and implementation of effective solutions based on best management practices. ater quality throughout Prince George’s County has been impacted by the conversionW of forest land to agricultural use over the past three centuries and to increasingly urbanized land over the past few decades. This conversion has resulted in degradation of streams, decline in forest and wetland habitats, and decreased opportunities to benefit from the recreational and economic opportunities that healthy water resources provide. Prince George’s County encompasses approximately 300,000 acres or five percent of the land area of Maryland and lies within the Chesapeake Bay watershed—the largest estuary in the United States and the third largest in the world. On May 12, 2009, President Barack Obama signed an executive order that recognizes the Chesapeake Bay as a national treasure and calls on the federal government to lead a renewed effort to restore and protect the nation’s largest estuary and its watershed.1 WATERSHEDS The term watershed is often applied to geographical areas of different sizes and scales. In general, the definition of a watershed is a geographic area in which water, sediments, and dissolved materials drain from higher elevations to a common low-lying outlet or basin discharging at a point on a larger stream, lake, underlying aquifer, or estuary.2 The largest watershed management unit is called a basin, which is a large drainage area related to a lake, river, or estuary, such as the Chesapeake Bay. Within each basin is a group of subbasins that can extend over hundreds of square miles. Maryland contains 13 subbasins, 1 http://www.cbf.org/site/MessageViewer?em_id=38823.0 2 http://www.stormwaterauthority.org/glossary.aspx Chapter V: Watershed Planning 55 Preliminary Water Resources Functional Master Plan HOWARD ten of which fall within the Chesapeake Bay basin and Watersheds COUNTY Prince George's County, Maryland ¯ correspond to ten tributary basins often referred to as Maryland’s “6-digit” watersheds as defined by the P A TU XE NT Maryland Department of Natural Resources (DNR). R IV ER MONTGOMERY COUNTY ANNE Subbasins contain groups of watersheds, which typically range from 20 to 100 square miles in size Upper Patuxent Anacostia and are composed of groups of subwatersheds that DISTRICT OF COLUMBIA cover an area of approximately ten square miles or less. ARUNDEL Maryland DNR has defined 138 watersheds, which are often referred to as Maryland’s “8-digit” watersheds. Western Branch They collectively contain the approximately 1,100 subwatersheds referred to as “12-digit” watersheds.3 Middle Patuxent Any of these units may be referred to as watersheds, Oxon Creek Patuxent DISTRICT OF COLUMBIA and depending on their size and location, contain a COUNTY number of land uses including forests, streams, and Wash Metro Area FAIRFAX Potomac other natural areas; agricultural and natural resource Middle Patuxent BROA D CREEK areas; urban, suburban, and rural communities; COUNTY Piscataway roadways and other transportation systems; commercial CALVERT C A M O T P O IS P CAT AWA Y CREEK development and industry; and schools, hospitals, CHARLES COUNTY COUNTY government offices and other public facilities. Water Lower Patuxent Lower Potomac Wash Metro Area resource issues including water supply, water quality, CHARLES COUNTY PA TU X and habitat for fish and wildlife are closely linked and E N Miles T R I V 0 5 10 E Legend R interdependent with human land uses. How land and Watershed Basin Main Watershed Oxon Creek Patuxent Anacostia Piscataway water resources are used have impacts on the entire bay Potomac Lower Patuxent Upper Patuxent watershed. Lower Potomac Wash Metro Area Middle Patuxent Western Branch Map 9: Watersheds IMPACTS OF LAND USE ON WATERSHEDS Prince George’s County’s landscape has changed dramatically over the past century along with other areas of the Chesapeake Bay watershed, particularly in and around the metropolitan Washington area. As we have spread across the watershed and built away from existing infrastructure, we are using more land than we need. Between 1970 and 2000, the watershed’s population increased by approximately eight percent. During this time, the average family size per household decreased but average home and lot sizes increased, and the amount of impervious surface area (roads, rooftops, parking lots, and other hardened or paved areas) increased by over 40 percent.4 This type of low density residential and commercial growth has extended to larger geographic areas within the county, resulting in more development outside existing municipalities, cities, and town centers. Expansion requires additional infrastructure in the form of more schools, roads, and shopping centers that increases pavement and roof areas. Open areas between developed areas have gradually filled with new development, which reduces the quantity, quality, and connectivity of forests, riparian buffers, wetlands, and agricultural lands. Forests and stream buffers provide critical 3 Center for Watershed Protection (CWP) User’s Guide 4 Ibid 56 Chapter V: Watershed Planning Preliminary Water Resources Functional Master Plan ecological services and act as buffers and filters within their watersheds; their loss causes increased pollution and degradation of land and water and, consequentially, quality of life for residents and visitors. Down-cutting: Population growth can result in economic benefits, but it can also have detrimental Downward or vertical impacts on natural resources if not planned for carefully to control the use of, and erosion is a geological avoid degradation to, water resources. Increasing populations require more domestic process that deepens the drinking water from available surface and groundwaters while increasing the amount of channel of a stream or valley wastewater and stormwater pollutants (point and nonpoint source) that are discharged into the receiving waters. In addition, during and after the development process, the by removing material from natural cycle of water is disrupted by alteration of the topography and the addition of the stream’s bed or the impervious surfaces that result in reduced water infiltration through soils to groundwater valley’s floor. How fast down- and increased quantities and velocities of runoff carrying sediments and pollutants to cutting occurs depends on streams. Stream flows are maintained through groundwater infiltration when rain falls the stream’s base level, which on forested or naturally vegetated areas. After development, the increase in impervious surfaces, decrease of soil functionality, and decrease in available groundwater mean that is the lowest point to which stream flows receive more surface runoff and associated pollutants at generally higher the stream can erode. temperatures. Sedimentation: The primary impacts to the hydrologic system from changes due to development include: The deposition of soil, sand, Changes in stream flow—increased runoff volumes, increased peak discharges, and minerals washed from greater runoff velocities, increased flooding, and lower dry weather stream flows. land into water, usually Changes in stream geometry—stream widening and down-cutting, loss of after rain. They pile up riparian tree cover, sedimentation in the channel, increased flood elevations, and disconnection of streams from adjacent wetlands and floodplains. in reservoirs, rivers and harbors, destroying fish and Degradation of aquatic habitat—degradation of habitat structure, loss of pool- riffle structure, reduced stream base flows, increased temperatures, and reduced wildlife habitat, and clouding abundance and diversity of aquatic biota. the water so that sunlight Water quality impacts—reduced dissolved oxygen and increases in nutrient cannot reach aquatic plants. enrichment, microbial contamination, hydrocarbons (oils and grease), toxic materials (pesticides, metals, and organic contaminants), sedimentation, increased Pool: temperatures, and trash/debris. A region of deeper slower- Impairment of drinking water supplies and increased cost of treatment. moving water with fine bed materials. Declining values of fisheries, waterfront properties, and loss of recreational uses (boating, fishing, swimming, etc.). Ripple: LOCAL WATER QUALITY ISSUES A region with coarse bed Degradation of the Chesapeake Bay has been recognized for decades, with excessive materials and shallow, fast nutrient loading identified as a critical problem. Major sources of nutrients include moving water sometimes urban, suburban, and agricultural runoff, failing septic systems and sewage treatment associated with whitewater. facilities, and atmospheric deposition from vehicles, power plants, and other sources. The pool-riffle is important Excess nutrients cause algal blooms that reduce the amount of sunlight available to submerged aquatic vegetation. Decomposition of the algae depletes bottom waters of in the cycling of nutrients oxygen, which causes “dead zones” and harms aquatic living resources such as blue in a stream. crabs and oysters. Other water quality issues affecting the bay include water pollution from sediments and chemicals, over-harvesting of aquatic resources, invasive plant and animal species, climate change, sea level rise, and tidal and nontidal