Land

The concept of the Green Infrastructure gives order and identity to the natural systems that support us. The Green Infrastructure provides essential “ecological services” that sustain life – nutrient cycling; storing, cleaning and conveying our water; cleaning the air we breathe, breaking down waste and creating topsoil; supporting food production, fishing and hunting; support for wildlife, and opportunities for humans to learn and enjoy our natural surroundings. A healthy Green Infrastructure is necessary to protect human health, support vibrant communities and a robust economy.

Loudoun County’s General Plan states that the Green Infrastructure “organizes the County’s environmental, natural and heritage resources into a related system consisting of the Potomac River edge, stream corridors and scenic rivers, forested areas and tree stands, mountainsides, wetlands, limestone conglomerate areas, important plant and wildlife habitats, greenways and trails, scenic areas and corridors, historic and archaeological sites, and other open spaces (natural, eased and man-made) of special importance. In all future land use planning, the framework of the Green Infrastructure will guide where and how development and redevelopment occurs.“

Why is the Green Infrastructure important?

The President’s Council on Sustainable Development defines Green Infrastructure as our nation’s natural life support system - an interconnected network of waterways, wetlands, woodlands, wildlife habitats, and other natural areas; greenways, parks and other conservation lands; working farms, ranches, and forests of conservation value; and wilderness and other open spaces that support native species, maintain natural ecological processes, sustain air and water resources and contribute to the health and quality of life for America’s communities and people.

What needs to be protected?

Sensitive areas are those most vulnerable to disruption by human interaction or areas that pose a potential threat to life and property from such actions as flooding, slope slippage, or sinkholes. Sensitive areas are components of the natural system that provides necessary “ecological services”. The areas must be protected to keep the integrity of natural processes intact. In most cases, these areas are difficult to develop or are specifically protected by County regulations. Sensitive areas include stream corridors, floodplains, wetlands, drinking water source areas, steep slopes, mountainsides, and areas underlain by limestone conglomerate.

Stream valleys are the “skeleton” of the Green Infrastructure.

Stream corridors may be the most important component of our natural environment. They collect and transport runoff and flood flows, carry base flow and groundwater, and recharge groundwater supplies. Stream valleys are home to a wide variety of plants and wildlife as well as some of the County’s grandest trees. They provide food, water, and travel corridors for wildlife, aid dispersal of native plant seeds, and offer exceptional opportunities for linear parks and trails. In addition, they serve critical ecological functions like helping clean our air and water, and supporting aquatic species that form the base of the food chain. Stream buffers – forested and vegetated areas adjacent to streams – protect against erosion and filter pollution before it gets into our water system.

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“Protecting the County’s Stream Corridors

must be a top priority in order to protect the

Green Infrastructure, protect nature, and reduce pollution.”

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Stream corridors also are a unique preservation opportunity. Since these valleys were often unsuitable for farming or development, many are in a relatively natural condition. Some of the County’s most remarkable habitats lie within stream valleys. Another important consideration is the high probability of archaeological or historical sites in, or near stream valleys. In both prehistoric and early historic periods, settlement occurred near reliable water sources. Preservation of stream corridors is a major step toward protecting some of our remaining historic structures and archaeological sites.

What makes an effective stream protection ordinance?

An effective strategy for protecting streams, adjacent floodplains and steep slopes, is critical to preserving ecological integrity, protecting watershed health, and retaining the interconnectivity of the Green Infrastructure. A stream corridor ordinance should be designed to protect the stream and adjacent resources. The regulation should also allow flexibility so that the best protection is achieved in concert with the needs of the landowner. Effective protection of the resource can be realized by applying a 3-zone concept to the stream corridor. In the 3-zone approach restrictions are the most extensive in the streamside zone where disturbance must be minimized and followed by restoration. Disturbance in the streamside zone has direct impacts on stream ecology and water quality.

The second zone is slightly less restrictive and encompasses the floodplain, adjacent wetlands, and steep slopes. Some uses are permitted within this “Middle Zone” provided the resources are protected and impacts mitigated. Disturbance in the Middle Zone may directly or indirectly affect stream ecology and could compromise the stream valley buffer.

The Outer Zone “buffers the buffer” with much more flexibility in uses and allowable disturbances. This zone can be managed with flexibility as long as the intent of the protective ordinance is served. Rather than a hard and fast dimension, this management area can shrink and grow as needed to protect sensitive areas and still accommodate the land use.

The former River and Stream Corridor Overlay District (RSCOD) was based on the 3-zone concept. This zoning overlay was overturned by the courts in 2004. In the absence of RSCOD or a similar ordinance, the County’s stream corridors are vulnerable to clearing and grading, multiple road and driveway crossings, utility encroachments, and other actions that threaten the resource.

What are wetlands and why are they so important?

Wetlands are areas where water is the dominant factor. Often they are low-lying areas with standing water but that is not always the case. A wetland can be periodically flooded or just contain saturated soil through part of the growing season. What constitutes a wetland is that flooding or soil saturation changes the soil chemistry and types of plants that grow there. Wetland soils have little or no oxygen in the pores (unlike a well aerated garden soil). These soils can often be identified by smell and/or color. Wetland soils are called “hydric soils“. In any case, a hydric soil is permanent evidence of a history of soil saturation, periodic flooding, or high water table.

Wetlands are over-achievers in some sense. On a global scale wetlands are only about 1.5 percent of the earth’s surface yet contribute nearly 40 percent of the global renewable ecosystem services. Wetlands are mostly in low-lying areas, so they store runoff during storm events and help prevent flooding and stream erosion. An acre of wetland can store over 1,000,000 gallons of water. They filter sediment and other pollutants from rainwater runoff. By storing polluted water for extended periods bacteria, contaminants and excess nutrients – all of which would be harmful once in our aquatic systems – are removed by wetlands.

Wetlands also provide valuable ecological functions. They support an abundance of aquatic and terrestrial wildlife. Although wetlands comprise only about 5 percent of the U.S. land area, they support about 31 percent of the plant species. Many species depend on wetlands during one or more periods of their life cycle and/or feed on organisms that develop in wetlands. About one-half of the nation’s birds species nest or feed in wetlands and 75 percent of commercially harvested fish are wetland dependent (95 percent when you include shellfish).

Conditions of flooding or saturated soil are very stressful to plants. Wetland vegetation must be specially adapted to periodic flooding, be able to resist flowing water, remain stable in wet muddy soils, and be able to survive where there is little or no oxygen present in the underlying soil. Wetland plants have developed adaptive strategies to overcome these conditions in order to survive.

Wetlands have long been either places of mystery that were avoided, or areas that man wanted to convert to “productive” farm land. Since the 1600s more than half of the original 220 million acres in the lower 48 states have been drained or filled. Only in recent decades have wetlands begun to receive protection through government regulations. Section 404 of the Clean Water Act protects wetlands against filling or draining. Today, impacts to wetlands are regulated by the U.S. Army Corps of Engineers (Corps) and Virginia Department of Environmental Quality (DEQ). The Corps and DEQ wetland permit processes require that applicants first seek to avoid impacts to wetlands. If avoidance is not feasible then onsite mitigation is preferred over off-site mitigation. Mitigation for wetland impacts may take several forms but the intent is to replace the ecological function lost by the wetland impact.

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Loudoun adopted the federal goal of

“no net loss” [of ecological function] of wetlands

with adoption of the County’s Revised General Plan.

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A relatively recent development in wetland mitigation is Wetland Banking. Wetland banks are areas where wetlands are created or re-established by investors and professional wetland scientists. Wetland banks must undergo a rigorous review and permit process prior to construction. Post-construction monitoring is conducted to demonstrate that the created wetland is functioning as anticipated. Wetland banks offer developers an alternative means of meeting state and federal mitigation requirements. Wetland banks sell pre-approved credits to applicants to satisfy all or part of the compensation required to offset an applicant’s wetland impact. The advantage of wetland banks is that a developer can purchase credits to fulfill permit obligations and avoid the lengthy process of designing and constructing compensatory wetlands. Mitigation banks can be used to consolidate compensation for a number of small impacts into one large wetland. If properly designed and constructed, a wetland bank may do a better job of replacing ecological function than is achieved by building several small, disconnected mitigation projects. The disadvantage of wetland banking is that historically many of the impacts in Loudoun were mitigated in adjacent counties like Prince William and Fauquier. Thanks to a joint County – Developer effort, this trend is changing. Wetland banks are being constructed in Loudoun so that mitigation for impacts can be kept at home.

What are floodplains and how are they protected?

A floodplain is flat land bordering a stream or river. When a stream or river overflows, the floodplain is covered with water. Floodplains help reduce stream erosion after large storms and store flood waters to help reduce downstream flooding. Floodplains are necessary to safely convey periodic flood flows so buildings are usually prohibited in floodplains under federal regulation and local ordinance. The Federal Emergency Management Agency (FEMA) administers a nationwide flood insurance program. Under FEMA’s regulations, structures cannot be built in a way that obstructs flood flows. If constructed on the fringe of a floodplain, structures must be built to be flood proof.

Loudoun County regulations are more restrictive. Structures (with very few exceptions) may not be constructed within the regulated floodplain. The County also requires that engineering studies accompany development applications in order to map the limits of the floodplain and evaluate if any proposed grading or crossings will impede flood flows or raise flood elevations. Floodplains are regulated by the County’s Floodplain Overlay District (FOD) Ordinance. The regulatory floodplain in Loudoun is defined by the extent of flooding resulting from a storm event having a one percent probability of occurring in any given year (sometimes referred to as the “100 year flood”). The ordinance protects safe passage of flood waters through residential communities and commercial districts. Having an effective ordinance with proper enforcement is also necessary for a community to participate in the Federal Flood Insurance Program.

Mountainsides are protected by the Mountainside Development Overlay District (MDOD)

The County Mountainside Development Overlay District (MDOD) places certain restrictions on development in areas defined under the MDOD. Mountainsides are important to the County for a number of reasons. These areas contain the County’s largest area of contiguous forest, feed headwater streams, recharge groundwater, and support plant and wildlife diversity. Loudoun’s mountains are also an important part of the character of the landscape by framing the Loudoun Valley and lending vistas to residents and visitors.

There are unique challenges to building in the mountainside areas. Slopes are usually steep which affects placement of roads, driveways, homes, wells and drainfields. Thin soil layers over shallow rock compound the difficulty of grading, excavation, and restabilizing disturbed areas. Steep slopes lead to high rates of soil erosion when mountainsides are cleared or disturbed and can have impacts that extend far beyond the construction footprint. Some mountainside areas also have a potential for rock slides and slope slippage. Because of these conditions, which vary from site to site, a site-specific locational clearance must be obtained from the County prior to grading or issuance of a building permit within the MDOD.

Steep Slopes

Steep slopes have many of the same construction challenges found on the mountainsides. Under the County ordinances Moderately Steep Slopes are slopes between 15 percent (8.5°) and 25 percent (14°). Very Steep Slopes are defined as those over 25 percent. The Steep Slope Ordinance defines steep slopes, requires avoidance of steep slopes to the extent possible and includes performance criteria for construction on or across steep slopes.

What is the Limestone area and why is protection important?

A large area just east of the Catoctin Mountain range in the Northeastern part of Loudoun County (pictured at right) is comprised of limestone and “Karst terrain” areas. The limestone geology of carbonate deposits dissolves over time by mildly acidic precipitation, creating fissures. These deposits are very permeable, allowing surface water to pass through quickly to underlying groundwater, sometimes reappearing elsewhere as springs. The terrain is also characterized by the presence of certain natural features, such as sinkholes and rock outcrops.

A Limestone Overlay District (LOD) Ordinance would regulate land use and development in areas underlain by limestone and in areas with Karst features and Karst terrain. This is important in order to protect groundwater from contamination and reduce the potential for property damage resulting from sink holes (pictured left) or other earth movement. Building in the Limestone Conglomerate area, like steep slopes and mountainside, has its own set of unique challenges. Conventional stormwater control methods such as wet or dry ponds concentrate pollutants and may contaminate groundwater. Modifications to the landscape could redirect surface flows contributing to sink holes and solution channels in the soft carbonate material beneath the surface. Individual waste treatment systems and erosion control methods both require special attention to the surface-subsurface connection to prevent surface or groundwater contamination. Geophysical testing is used as a means of testing the underlying geology prior to construction permitting, and before locating buildings or other structures.

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Native species and ecosystems are important to protect for many reasons. They provide valuable, if not irreplaceable, ecosystem services and other economic benefits; and they offer humans aesthetic and spiritual nourishment.

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Drinking water source areas

There are several drinking water sources in Loudoun. The City of Fairfax owns Goose Creek Reservoir. This drinking water reservoir is fed by Goose Creek. Beaverdam Creek Reservoir lies just upstream of Goose Creek Reservoir. Water impounded in Beaverdam Creek Reservoir is released when necessary to augment supply at the water intake. Loudoun County Sanitation Authority (LCSA) purchases water from the City of Fairfax as supply to Ashburn. The balance of water purchased by LCSA comes from Fairfax [County] Water’s Potomac River intake. The Town of Purcellville owns Hirst Reservoir as a drinking water supply. There are a few communal and municipal wells that serve the Towns and select communities in Western Loudoun. Individual wells serve residents outside of the service areas of LCSA and the Towns.

Source water protection is an issue being addressed by many counties and municipalities to protect drinking water. Supplemental land use restrictions in areas that directly contribute to surface or groundwater used for drinking supplies can help protect the quality of the water and reduce treatment costs. Several strategies can be employed, some as simple as requiring greater setbacks from reservoirs. Other protective strategies can include overlay zones that restrict certain land uses or require a greater degree of pollution prevention; multiple barrier approaches to pollution prevention so that there is redundancy and higher levels of protection; and public education programs to show businesses and landowners how to prevent pollution at the source.

What are the major threats to these sensitive areas?

Sensitive areas like Big Spring Creek (Loudoun’s only trout stream) pictured here, are more vulnerable to land disturbances associated with agriculture or land development. Although resources can be threatened by natural disasters, in Loudoun County rapid growth has been the principal stressor. The next four years will see nearly 40,000 new residents. As growth continues 2030 will see an additional 200,000 residents and 121 percent job growth (source: MWCOG). The pressure on our natural systems will mount. The challenge is to accommodate needed jobs and housing without an expensive ecological collapse and loss of “quality of life”.

Growth can occur in balance with protection of the County’s water, nature, and sensitive areas. Design for new developments must begin by first identifying important natural and cultural resources. This initial step delineates areas where land disturbance should be avoided or minimized. Once areas set aside for resource protection have been mapped, the remaining property area can be laid out for development. Flexibility must be built into the process so that innovative proposals that give a higher level of resource protection can be encouraged, not discouraged with unyielding regulation. This process goes by various names – Conservation Design, Environmentally Sensitive Development (ESD), or Green Design.