Managing Water Quality and Quantity in One Facility
Improving water quality and reducing flood damage become compatible goals.
By
George W. Simpson,
Robert H Wampler,
Charles E. Mitchem,
Christy Straight
The design of the new Hidden Valley High School Stormwater Management Facility (Hidden Valley SWMF) in Roanoke County, VA, was shaped by the need to improve water quality and reduce flood damage. The facility will not only reduce the increase in post-developed storm flows in Mud Lick Creek by as much as 101% (in two-year events), but its pollutant-reduction features will also benefit the health of the Roanoke River, a 303(d)-listed river. An extended detention basin, enhanced by a forebay and downstream riparian buffer, best serves the existing and anticipated 2020 development scenarios for mitigating flooding and controlling the pollutant loads in Mud Lick Creek.
A regional stormwater management plan was developed for the Roanoke Valley in 1997 and identified projected growth to 2020 and the flooding impacts of that growth in the area's 16 watersheds of the Roanoke River. The plan identified water-quantity control measures in each watershed. Within Mud Lick Creek, two best management practice (BMP) locations were recommended to mitigate impacts of development. Land use is expected to be 50% high-density, 30% low-density, and 10% medium-density in hilly terrain of Blue Ridge and Valley and Ridge geologic provinces.
 |
| The project site in in the southwest area of the county. Major highways are indicated by white lines. The Roanoke River runs east and is in blue. |
Implementing the Plan
In 1999, Roanoke County had the opportunity to construct one of the recommended facilities on Mud Lick Creek. The Roanoke County School Board was constructing a new 70-acre-campus high school that required a stormwater management facility next to the creek. A regional stormwater management facility had been identified on that site in the county's regional master plan, but neither the school board nor the county's board of supervisors had allocated funding for it. By pursuing funding at the state level through the Department of Conservation and Recreation's Water Quality Improvement Act grants, and with endorsement by the local greenway commission and Project Impact, the county could create a regional facility owned by the school board and maintained by the county.
To make the most of this opportunity, Roanoke County added a water-quality goal to the project. The design criteria were modified to include the reduction of nutrients, metals, and sediment loads in accordance with the Commonwealth of Virginia's stormwater regulations, even though the project was not required to design to those standards, as National Pollutant Discharge Elimination System (NPDES) requirements were still years away from implementation. The water quality element made the county eligible for funds under Virginia's Water Quality Improvement Act with $230,000 in a 50% matching grant.
Historical and Projected Watershed Character
The facility is situated 4.5 miles above the mouth of the 6.2-mile-long creek and receives flow from 1,218 acres of the 6,121-acre watershed. Water flows are expected to increase in each storm event based on projected development and known changes in land use since the 1997 plan. The flow estimates assume a 30% impervious surface area in 2020 (compared to an existing 15%). Table 1 summarizes existing and future flow rates.
The flow rates were calculated using the drainage area of 1,218.8 acres, the time-of-concentration of 1.26 hours, the existing curve number value of 67.9, and a future curve number value of 73.9.
Flooding
Riverine flooding in the Roanoke River watershed is typically well documented. The Roanoke Valley has experienced 17 large flood events since 1877. Four in the last 30 years have been significant: one 50-year, one 130-year, and two 10-year storm events.
The Mud Lick Creek watershed contains 13 specific land uses, but more than 50% of the watershed is composed of 0.25-acre residential lots. According to the Roanoke Valley Regional Stormwater Management Plan, there are approximately 60 houses in the 100-year floodplain of Mud Lick Creek. Forty of those are also affected by 10-year storm events. Since the Hidden Valley SWMF began operation in 2000 and despite drought conditions in 2002, several flood events occurred in the spring of 2003. The facility appears to have made a difference—no roads have flooded and residents have seen little or no damage to their homes from these storms.
Pollutant Loads
Hidden Valley SWMF will reduce phosphorus, nitrogen, suspended solids, lead, and zinc loadings through differential settling and biological uptake. Settling efficiency and, to some extent, biological uptake and transformation are dependent on runoff detention time and the presence of appropriate wetland and aquatic vegetation. The 30-hour drawdown and forebay treat runoff from small, more frequent storms, increasing pollutant removal efficiency. The extended detention basin is an effective, low-cost means of removing particulate pollutants and controlling downstream bank erosion.
The facility will accomplish reductions in total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), lead (Pb), and zinc (Zn). The loadings and reductions were determined with simplified, planning-level hydrologic techniques. Pollutant loads are calculated with the equation
where
- L = pollutant load (lb/yr)
- P = annual average precipitation (in/yr)
- Pj = rainfall correction factor
- Rv = runoff coefficient
- EMC = pollutant event mean concentration (mg/lit)
- A = watershed area (ac)
- 12 and 2.72 are conversion factors where 12 inches = 1 foot and 2.72 lb/yr = [(ft/yr)(mg/lit)(ac)]x[(43,560 sf/ac)(lb/453,593 mg)(28.317 lit/cf)] (from EPA's Guidance Manual for Preparation of Part 2 of the NPDES Permit Application for Discharges from Municipal Separate Storm Sewer Systems)
The basis of the equation is water-quality parameters related to land use and soil type.
Table Two
Design
 |
| The extended detention basin, an in-line facility, was selected during the feasibility study based on site and design constraints. |
Using Virginia's stormwater regulations as a guide, the facility was designed to treat the "first flush' (the first half-inch of rainfall runoff, also referred to as water-quality volume, or WQV) and reduce flooding in two-year and ten-year storm events. The selected facility needed to meet these requirements based on the county's goal of optimizing design to meet the highest water quality possible downstream and to fit into the available acreage.
The land available for the facility covers 6 acres along the creek. The site is bounded by the high school at the top of the western slope; residential development and school athletic fields to the east; Canter Road, which crosses the creek, to the south; and the school's access road (which would also serve as the facility's emergency spillway) to the north. Because of the fixed dimensions of the site, options reducing pollutant loads and providing effective flood management were limited to detention or retention basins.
The consulting engineer, Engineering Concepts Inc. (ECI), evaluated three alternatives based on the total contributing watershed area and the infiltration rate of soils at the facility. Each of the following alternatives was evaluated and included a wetland-enhanced forebay: extended detention, enhanced extended detention, and a retention basin. The results of the feasibility study clearly demonstrated that the extended detention basin was the most appropriate choice. The alternatives are summarized in Table 3.
The constructed design, an extended detention basin with a forebay, stream restoration, and downstream riparian buffer, begins 85 feet downstream of Canter Road. The forebay, which can handle a total volume of 5 acre-feet, will be most effective in sediment deposition during one-year events. The forebay receives the stream flow through a single 24-inch culvert in low flows or through a 20-foot-wide channel during higher flows and discharges to the detention basin through three 60-inch pipes. The online detention basin is in a physical depression banked by a 20% slope to the east and a re-graded 50% slope that fits the high school site design to the west.
 |
| Students from Hidden Valley High School practice water-sampling techniques during a field laboratory session. |
The facility's embankment, which incorporates three overflow outlet structures, also serves as the school's access road. At the base of the embankment, a 24-inch pipe releases normal stream flow. For ease of pipe maintenance, a shallow sediment pit was excavated at each end of the pipe. An 18-inch orifice plate and a debris rack control accumulation within the pipe. The original debris rack required frequent monitoring and maintenance to maintain its expected effectiveness. Mats of leaves, soda bottles, and other small debris caught by the rack caused restrictions too often for long-term maintenance of the facility. The rack has since been redesigned to allow smaller debris to flow through the pipe but still blocks larger material, such as tree branches or other large debris, that could clog the base flow pipe.
The overflow structure allows a 30-hour drawdown of twice the WQV (the first half-inch of rainfall runoff from the 30% impervious surface area of the 1,218-acre watershed releases flows from two-year events at predeveloped rates and can safely pass half of the probable maximum flood (a flow six times that of the 100-year flood). Anticipated effectiveness of the facility's reduction of increased flows for other events is included in Table 4.
The overflow outlets control the flow during two-year storm events and larger floods. The overflow consists of three 12.5-foot-diameter structural plate pipes. The structural plate was selected for the overflow pipes to match materials already specified for construction, thereby avoiding increased costs or schedule delays. The overflow outlet releases into a riprap-lined basin and flow channel 45 feet to the east of the existing creek. The scour hole normally created by high-velocity flows has been excavated and lined with riprap sufficient to handle flow velocity resulting from a 100-year event. The flow channel is lined with a turf reinforcement geotextile to provide natural cover and withstand 100-year storm flows.
Riparian buffer improvements were added to the streambank within the detention basin and along 50 feet of the streambank past the downstream base flow outlet. Plantings will improve the streambank's stability and mitigate erosion as well as reduce flow velocity. The riparian buffer will also provide shade to reduce water temperature and improve stream habitat as well as improve the visual impacts of the basin.
Coordinating Construction
 |
 |
 |
| The outlet for normal stream flows during construction, during a storm event, and with normal stream flows at normal levels. |
Once funding was acquired, Hidden Valley SWMF was included as an addendum to the overall construction package. ECI, also the engineer for the school's site design, coordinated site construction activities with the general contractor to phase site work to accommodate the anticipated addendum and modify the road design.
Construction on the SWMF required diverting the stream flow while installing the base flow pipe. The county was fortunate to have a cooperative contractor with Counts and Dobyns, who phased their activities and budgeted to accommodate the addendum for the facility.
Effectiveness of Facility—Water Quality and Quantity
The consulting engineer also developed a monitoring program to assess the health of Mud Lick Creek, which the county began implementing during construction. The overall goals for the monitoring program are to qualitatively monitor stream health and quantitatively determine the effectiveness of the SWMF. The original program, routine and event-based sampling, called for volunteer monitoring because no budgeted funds were available. The current monitoring plan, begun in June 2001, is an impact monitoring program intended to assess the performance of the SWMF by examining various water-quality parameters upstream, downstream, and within the facility.
Before construction of the facility, no existing data were available for a baseline of stream health. When testing was conducted monthly during construction and the first nine months of the SWMF's operation, a baseline was established to determine the effectiveness of the facility and the stream's health.
In the first year of implementation, routine samples were collected quarterly and four storm events were monitored in three locations. In April 2002, the monitoring program design was changed at the request of the state regulatory agency (Virginia Department of Conservation and Recreation) to eliminate the routine sampling in favor of more event sampling with the first year of sampling used as the baseline data. The program has been reconfigured to sample events of various durations and intensities at the original three locations. The drought conditions of 2002 affected the number and magnitude of storm events suitable for sampling, so monitoring was performed only five times.
The samples collected are analyzed in the field for pH, temperature, and dissolved oxygen concentration, and additional grab samples are sent to a certified laboratory for TSS, total Kjeldahl nitrogen, and TP analyses. Because of lag effects, such as hydraulic adjustment and growth of plantings for erosion control in the facility, the monitoring program does not have a fixed end date.
With these water-quality and water-quantity data parameters, meaningful observations can, in time, be made about the stream health and the performance of the SWMF. Monitoring data are still being collected, and until a sufficient number of data points are collected to constitute a valid statistical sample, no conclusions can be drawn.
Beyond Passive Quality and Quantity Control
 |
| The overflow outlets are designed to accommodate the 100-year flood. |
Hidden Valley SWMF contributes to the county's goal of creating physical control measures, but it also provides an educational resource and an ideal situation to monitor and measure stormwater management effectiveness in the county's watersheds.
Field Laboratory for Students
Roanoke County has incorporated Hidden Valley SWMF into its NPDES implementation plan, not just as a physical BMP, but also as a minimum control measure both for public education and outreach and for public participation and involvement through stream school seminars and Save Our Streams programs for macroinvertebrate assessment and stream habitat inventory. The county's community development department, working with Virginia's Save Our Streams, the Roanoke County school system, and Explore Park, has already held these events in 2003 for high school students. Plans for future events include participation of the local community-college students and at least 10% of the county's school-age children.
Future Monitoring and Improvements at Hidden Valley SWMF
Beyond the current monitoring program discussed above, the county has outlined its goals for developing meaningful data on the stream's water quality and the SWMF's impact on the stream and has begun to implement those goals. Plans for upgrading and expanding data collection efforts include a water-quality database for flows from the detention area, cross-sections and global positioning system profiles within the basin, a database of macroinvertebrate populations, more data collection points for pollutant reduction trend analysis, flood stage indicators and gauging stations, and automatic samplers for composite water-quality sampling stations. Additional water-quality control measures—biofiltration—downstream of the SWMF have been installed to collect sediments not captured by the SWMF.
Advertisement
Summary
As communities continue to grow and development intensifies and expands, municipalities must seek resourceful solutions to address the increase in stormwater runoff and to mitigate potential flooding problems. NPDES regulations require local governments to reduce nonpoint-source pollutants, an issue particularly compelling for governments facing imminent deadlines for compliance and total maximum daily load plans. Stormwater solutions must focus on both issues. Additionally, addressing water-quality issues and water-quantity control now extends to basin-wide solutions, not just site-specific controls for new development. These basin-wide solutions are most effective when based on projections developed in long-term, regional plans, such as Roanoke Valley's stormwater management plan. This 20-year plan allowed Roanoke County to clarify the need for stormwater management facilities and identify potential sites. The county was therefore in a position to recognize and make the most of an opportunity to design and construct a stormwater facility, for only the cost of design and construction, that will improve the health of the Mud Lick Creek watershed and reduce flooding for residents now and through 2020.
Author's Bio: George W. Simpson III, P.E., is assistant director of community development for Roanoke County, VA.
Author's Bio: Robert H. Wampler, P.E., is design manager with Engineering Concepts Inc. in Fincastle, VA.
Author's Bio: Charles E. Mitchem Jr., P.E., is an environmental engineer with Engineering Concepts Inc. in Fincastle, VA.
Author's Bio: Christy Straight is marketing coordinator with Engineering Concepts Inc. in Fincastle, VA.
September-October 2004
Managing Water Quality and Quantity in One Facility
Improving water quality and reducing flood damage become compatible goals.
By
George W. Simpson,
Robert H Wampler,
Charles E. Mitchem,
Christy Straight
The design of the new Hidden Valley High School Stormwater Management Facility (Hidden Valley SWMF) in Roanoke County, VA, was shaped by the need to improve water quality and reduce flood damage. The facility will not only reduce the increase in post-developed storm flows in Mud Lick Creek by as much as 101% (in two-year events), but its pollutant-reduction features will also benefit the health of the Roanoke River, a 303(d)-listed river. An extended detention basin, enhanced by a forebay and downstream riparian buffer, best serves the existing and anticipated 2020 development scenarios for mitigating flooding and controlling the pollutant loads in Mud Lick Creek.A regional stormwater management plan was developed for the Roanoke Valley in 1997 and identified projected growth to 2020 and the flooding impacts of that growth in the area's 16 watersheds of the Roanoke River. The plan identified water-quantity control measures in each watershed. Within Mud Lick Creek, two best management practice (BMP) locations were recommended to mitigate impacts of development. Land use is expected to be 50% high-density, 30% low-density, and 10% medium-density in hilly terrain of Blue Ridge and Valley and Ridge geologic provinces.
|
| The project site in in the southwest area of the county. Major highways are indicated by white lines. The Roanoke River runs east and is in blue. |
Implementing the Plan
In 1999, Roanoke County had the opportunity to construct one of the recommended facilities on Mud Lick Creek. The Roanoke County School Board was constructing a new 70-acre-campus high school that required a stormwater management facility next to the creek. A regional stormwater management facility had been identified on that site in the county's regional master plan, but neither the school board nor the county's board of supervisors had allocated funding for it. By pursuing funding at the state level through the Department of Conservation and Recreation's Water Quality Improvement Act grants, and with endorsement by the local greenway commission and Project Impact, the county could create a regional facility owned by the school board and maintained by the county.
To make the most of this opportunity, Roanoke County added a water-quality goal to the project. The design criteria were modified to include the reduction of nutrients, metals, and sediment loads in accordance with the Commonwealth of Virginia's stormwater regulations, even though the project was not required to design to those standards, as National Pollutant Discharge Elimination System (NPDES) requirements were still years away from implementation. The water quality element made the county eligible for funds under Virginia's Water Quality Improvement Act with $230,000 in a 50% matching grant.
Historical and Projected Watershed Character
The facility is situated 4.5 miles above the mouth of the 6.2-mile-long creek and receives flow from 1,218 acres of the 6,121-acre watershed. Water flows are expected to increase in each storm event based on projected development and known changes in land use since the 1997 plan. The flow estimates assume a 30% impervious surface area in 2020 (compared to an existing 15%). Table 1 summarizes existing and future flow rates.
The flow rates were calculated using the drainage area of 1,218.8 acres, the time-of-concentration of 1.26 hours, the existing curve number value of 67.9, and a future curve number value of 73.9.
Flooding
Riverine flooding in the Roanoke River watershed is typically well documented. The Roanoke Valley has experienced 17 large flood events since 1877. Four in the last 30 years have been significant: one 50-year, one 130-year, and two 10-year storm events.
The Mud Lick Creek watershed contains 13 specific land uses, but more than 50% of the watershed is composed of 0.25-acre residential lots. According to the Roanoke Valley Regional Stormwater Management Plan, there are approximately 60 houses in the 100-year floodplain of Mud Lick Creek. Forty of those are also affected by 10-year storm events. Since the Hidden Valley SWMF began operation in 2000 and despite drought conditions in 2002, several flood events occurred in the spring of 2003. The facility appears to have made a difference—no roads have flooded and residents have seen little or no damage to their homes from these storms.
Pollutant Loads
Hidden Valley SWMF will reduce phosphorus, nitrogen, suspended solids, lead, and zinc loadings through differential settling and biological uptake. Settling efficiency and, to some extent, biological uptake and transformation are dependent on runoff detention time and the presence of appropriate wetland and aquatic vegetation. The 30-hour drawdown and forebay treat runoff from small, more frequent storms, increasing pollutant removal efficiency. The extended detention basin is an effective, low-cost means of removing particulate pollutants and controlling downstream bank erosion.
The facility will accomplish reductions in total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), lead (Pb), and zinc (Zn). The loadings and reductions were determined with simplified, planning-level hydrologic techniques. Pollutant loads are calculated with the equation
where
- L = pollutant load (lb/yr)
- P = annual average precipitation (in/yr)
- Pj = rainfall correction factor
- Rv = runoff coefficient
- EMC = pollutant event mean concentration (mg/lit)
- A = watershed area (ac)
- 12 and 2.72 are conversion factors where 12 inches = 1 foot and 2.72 lb/yr = [(ft/yr)(mg/lit)(ac)]x[(43,560 sf/ac)(lb/453,593 mg)(28.317 lit/cf)] (from EPA's Guidance Manual for Preparation of Part 2 of the NPDES Permit Application for Discharges from Municipal Separate Storm Sewer Systems)
The basis of the equation is water-quality parameters related to land use and soil type.
Table Two
Design
|
| The extended detention basin, an in-line facility, was selected during the feasibility study based on site and design constraints. |
Using Virginia's stormwater regulations as a guide, the facility was designed to treat the "first flush' (the first half-inch of rainfall runoff, also referred to as water-quality volume, or WQV) and reduce flooding in two-year and ten-year storm events. The selected facility needed to meet these requirements based on the county's goal of optimizing design to meet the highest water quality possible downstream and to fit into the available acreage.
The land available for the facility covers 6 acres along the creek. The site is bounded by the high school at the top of the western slope; residential development and school athletic fields to the east; Canter Road, which crosses the creek, to the south; and the school's access road (which would also serve as the facility's emergency spillway) to the north. Because of the fixed dimensions of the site, options reducing pollutant loads and providing effective flood management were limited to detention or retention basins.
The consulting engineer, Engineering Concepts Inc. (ECI), evaluated three alternatives based on the total contributing watershed area and the infiltration rate of soils at the facility. Each of the following alternatives was evaluated and included a wetland-enhanced forebay: extended detention, enhanced extended detention, and a retention basin. The results of the feasibility study clearly demonstrated that the extended detention basin was the most appropriate choice. The alternatives are summarized in Table 3.
The constructed design, an extended detention basin with a forebay, stream restoration, and downstream riparian buffer, begins 85 feet downstream of Canter Road. The forebay, which can handle a total volume of 5 acre-feet, will be most effective in sediment deposition during one-year events. The forebay receives the stream flow through a single 24-inch culvert in low flows or through a 20-foot-wide channel during higher flows and discharges to the detention basin through three 60-inch pipes. The online detention basin is in a physical depression banked by a 20% slope to the east and a re-graded 50% slope that fits the high school site design to the west.
|
| Students from Hidden Valley High School practice water-sampling techniques during a field laboratory session. |
The facility's embankment, which incorporates three overflow outlet structures, also serves as the school's access road. At the base of the embankment, a 24-inch pipe releases normal stream flow. For ease of pipe maintenance, a shallow sediment pit was excavated at each end of the pipe. An 18-inch orifice plate and a debris rack control accumulation within the pipe. The original debris rack required frequent monitoring and maintenance to maintain its expected effectiveness. Mats of leaves, soda bottles, and other small debris caught by the rack caused restrictions too often for long-term maintenance of the facility. The rack has since been redesigned to allow smaller debris to flow through the pipe but still blocks larger material, such as tree branches or other large debris, that could clog the base flow pipe.
The overflow structure allows a 30-hour drawdown of twice the WQV (the first half-inch of rainfall runoff from the 30% impervious surface area of the 1,218-acre watershed releases flows from two-year events at predeveloped rates and can safely pass half of the probable maximum flood (a flow six times that of the 100-year flood). Anticipated effectiveness of the facility's reduction of increased flows for other events is included in Table 4.
The overflow outlets control the flow during two-year storm events and larger floods. The overflow consists of three 12.5-foot-diameter structural plate pipes. The structural plate was selected for the overflow pipes to match materials already specified for construction, thereby avoiding increased costs or schedule delays. The overflow outlet releases into a riprap-lined basin and flow channel 45 feet to the east of the existing creek. The scour hole normally created by high-velocity flows has been excavated and lined with riprap sufficient to handle flow velocity resulting from a 100-year event. The flow channel is lined with a turf reinforcement geotextile to provide natural cover and withstand 100-year storm flows.
Riparian buffer improvements were added to the streambank within the detention basin and along 50 feet of the streambank past the downstream base flow outlet. Plantings will improve the streambank's stability and mitigate erosion as well as reduce flow velocity. The riparian buffer will also provide shade to reduce water temperature and improve stream habitat as well as improve the visual impacts of the basin.
Coordinating Construction
|
|
|
| The outlet for normal stream flows during construction, during a storm event, and with normal stream flows at normal levels. |
Once funding was acquired, Hidden Valley SWMF was included as an addendum to the overall construction package. ECI, also the engineer for the school's site design, coordinated site construction activities with the general contractor to phase site work to accommodate the anticipated addendum and modify the road design.
Construction on the SWMF required diverting the stream flow while installing the base flow pipe. The county was fortunate to have a cooperative contractor with Counts and Dobyns, who phased their activities and budgeted to accommodate the addendum for the facility.
Effectiveness of Facility—Water Quality and Quantity
The consulting engineer also developed a monitoring program to assess the health of Mud Lick Creek, which the county began implementing during construction. The overall goals for the monitoring program are to qualitatively monitor stream health and quantitatively determine the effectiveness of the SWMF. The original program, routine and event-based sampling, called for volunteer monitoring because no budgeted funds were available. The current monitoring plan, begun in June 2001, is an impact monitoring program intended to assess the performance of the SWMF by examining various water-quality parameters upstream, downstream, and within the facility.
Before construction of the facility, no existing data were available for a baseline of stream health. When testing was conducted monthly during construction and the first nine months of the SWMF's operation, a baseline was established to determine the effectiveness of the facility and the stream's health.
In the first year of implementation, routine samples were collected quarterly and four storm events were monitored in three locations. In April 2002, the monitoring program design was changed at the request of the state regulatory agency (Virginia Department of Conservation and Recreation) to eliminate the routine sampling in favor of more event sampling with the first year of sampling used as the baseline data. The program has been reconfigured to sample events of various durations and intensities at the original three locations. The drought conditions of 2002 affected the number and magnitude of storm events suitable for sampling, so monitoring was performed only five times.
The samples collected are analyzed in the field for pH, temperature, and dissolved oxygen concentration, and additional grab samples are sent to a certified laboratory for TSS, total Kjeldahl nitrogen, and TP analyses. Because of lag effects, such as hydraulic adjustment and growth of plantings for erosion control in the facility, the monitoring program does not have a fixed end date.
With these water-quality and water-quantity data parameters, meaningful observations can, in time, be made about the stream health and the performance of the SWMF. Monitoring data are still being collected, and until a sufficient number of data points are collected to constitute a valid statistical sample, no conclusions can be drawn.
Beyond Passive Quality and Quantity Control
|
| The overflow outlets are designed to accommodate the 100-year flood. |
Hidden Valley SWMF contributes to the county's goal of creating physical control measures, but it also provides an educational resource and an ideal situation to monitor and measure stormwater management effectiveness in the county's watersheds.
Field Laboratory for Students
Roanoke County has incorporated Hidden Valley SWMF into its NPDES implementation plan, not just as a physical BMP, but also as a minimum control measure both for public education and outreach and for public participation and involvement through stream school seminars and Save Our Streams programs for macroinvertebrate assessment and stream habitat inventory. The county's community development department, working with Virginia's Save Our Streams, the Roanoke County school system, and Explore Park, has already held these events in 2003 for high school students. Plans for future events include participation of the local community-college students and at least 10% of the county's school-age children.
Future Monitoring and Improvements at Hidden Valley SWMF
Beyond the current monitoring program discussed above, the county has outlined its goals for developing meaningful data on the stream's water quality and the SWMF's impact on the stream and has begun to implement those goals. Plans for upgrading and expanding data collection efforts include a water-quality database for flows from the detention area, cross-sections and global positioning system profiles within the basin, a database of macroinvertebrate populations, more data collection points for pollutant reduction trend analysis, flood stage indicators and gauging stations, and automatic samplers for composite water-quality sampling stations. Additional water-quality control measures—biofiltration—downstream of the SWMF have been installed to collect sediments not captured by the SWMF.
Summary
As communities continue to grow and development intensifies and expands, municipalities must seek resourceful solutions to address the increase in stormwater runoff and to mitigate potential flooding problems. NPDES regulations require local governments to reduce nonpoint-source pollutants, an issue particularly compelling for governments facing imminent deadlines for compliance and total maximum daily load plans. Stormwater solutions must focus on both issues. Additionally, addressing water-quality issues and water-quantity control now extends to basin-wide solutions, not just site-specific controls for new development. These basin-wide solutions are most effective when based on projections developed in long-term, regional plans, such as Roanoke Valley's stormwater management plan. This 20-year plan allowed Roanoke County to clarify the need for stormwater management facilities and identify potential sites. The county was therefore in a position to recognize and make the most of an opportunity to design and construct a stormwater facility, for only the cost of design and construction, that will improve the health of the Mud Lick Creek watershed and reduce flooding for residents now and through 2020.