Frequently Asked Questions
- Who do I contact if I have a question or concern regarding this project?
- Where can I get information on upcoming public meetings and events regarding this project?
- Why is the trail closed? How will I get to where I'm going?
- What is the Northern Virginia Stream Restoration Bank?
- What is mitigation banking?
- What is HB 2464?
- Why are we creating a stream bank in Reston?
- What benefit will Reston see?
- How do we know if the restoration is successful?
- Reston has preserved all of its streams, so they should be fine. What gives?
- What's wrong with the streams the way they are?
- How will stream restoration help our environment?
- Is there a difference between urban and rural streams?
- Can't we just dredge the sediment out of the ponds once in a while?
- Will you get rid of all the beavers?
- Why is there so much algae in the streams? Is it detrimental?
- What is the design process?
- What are those little silver tags on all the trees?
- Are you straightening the stream? If so, why?
- Will the pools create mosquito breeding habitat?
- What plants are you planting? Are they native to Reston?
- Why are you planting seedlings instead of container-grown stock? Won't they take a long time to grow?
- Why aren't you using tree tubes to help the new trees survive?
- Aren't you removing existing streamside habitat?
- Will the stream restoration increase the flooding potential in my basement?
- Why have some of the bridges moved?
- How will the restoration project affect deer and other species?
- Do you have to remove trees? If so, how do you assess the "value" of one tree over another?
- What is the "stockpile area" used for?
- Why have I seen a few white PVC pipes scattered randomly throughout the streams?
- What is the basis for the spacing on the construction access “cut-ins,” and why can’t the distance between them be increased?
Who do I contact if I have a question or concern regarding this project?
Contact the Reston Association with questions regarding this project. They are responsible for easements, public meetings, trail maintenance and operation during construction, and other matters. If you have a technical question, they will gladly forward it to Wetland Studies to get it answered or included here.
Where can I get information on upcoming public meetings and events regarding this project?
Why is the trail closed? How will I get to where I'm going?
We apologize for any inconvenience, but for safety and liability reasons, trails in the vicinity of the stream work will be closed and blocked off with orange fencing. Signed detour routes will be provided to allow access around the work area. Trail patrons with time constraints should allow for a few extra minutes if they suspect they may be travelling in the vicinity of the work area.
What is the Northern Virginia Stream Restoration Bank?
The Northern Virginia Stream Restoration Bank (NVSRB) is a partnership between Wetland Studies and Solutions, Inc. (WSSI) and the Reston Association. The NVSRB is responsible for restoring and stabilizing degraded streams in Reston.
What is mitigation banking? How does it work?
First, a Public Works Agency or private landowner needs to impact streams on their property. In the past, they would have had to restore streams as compensation, either on or off their site.
Under the market-oriented system, they can go to a “bank” created by a Bank Sponsor who has obtained credit for restoring impaired streams elsewhere in the same portion of the rivershed & physiographic province.
By purchasing stream credits from the Bank Sponsor, the mitigation requirements of a permit for stream impacts is satisfied. Stream restorers use this pooled money to create much larger, well-designed, & ecologically valuable conservation projects.
What is HB 2464?
House Bill (HB) 2464 was a law written by WSSI, submitted by Patrons Rust and Plum, and signed by the Governor in 2005. HB 2464 allows natural stream designs to function as intended by stating that, "Stream restoration and relocation projects that incorporate natural channel design concepts are not man-made channels and shall be exempt from any flow rate capacity and velocity requirements for natural or man-made channels as defined in any regulations promulgated pursuant to this section."
Stormwater regulations, originially intended to regulate concrete or rip-rap stormwater conveyance channels, require designers to contain both the 2-year storm event and the 10-year storm event within the banks of the channels to reduce flooding and damage potential. Physically, this requirement concentrates all of the flow energy of these storms within the channel itself. While concrete channels are strong enough to carry these high flows, natural streams must dissipate that high-flow energy by overtopping their banks more frequently than the 2-year event (let alone the 10-year event). If a natural stream doesn't dissipate some of the energy into the floodplain, soil particles are torn from the stream bank by the high-energy water, causing incision, downcutting, and downstream sedimentation- all of which are issues for Reston's streams.
NEEDS UPDATE [maybe "why have we created...] - Why are we creating a stream bank in Reston?
The following are four reasons that it makes sense to build a stream bank in Reston.
1. Degrading streams are located in preserved corridors (without stormwater management) and are mostly controlled by a single entity (Reston Association);
2. Community members are actively involved in protecting local natural resources (i.e. Watershed Plan published in April 2002);
3. The community of Reston includes entire watersheds; and
4. There is a demand for stream mitigation in the region - the Bank service area is determined by HUC and Physiographic Province.
NEEDS UPDATE OR TO BE DELETED - What benefit will Reston see?
At the completion of Phase I of the project, the Reston Association will have received $400,000, and Friends of Reston will have received $650,000. In addition, Reston will have had its streams, and their assoicated environmental benefit, restored for the benefit of all Reston citizens.
NEEDS UPDATE - How do we know if the restoration is successful?
WSSI is required to conduct a 10-year monitoring program as part of the Mitigation Banking agreement. During the monitoring period, we will conduct streambed, structure, vegetation, and biological surveys. The purpose of these surveys is to determine if any structure or streambed failure has occured; if the vegetation has established and is thriving; and if wildlife (from bugs to frogs to turtles) has begun to make use of the new habitat. If any of these parameters show signs of failure during the monitoring period, we will return to correct the problem. After 10 years, the project will be turned over to the Reston Association and Friends of Reston for long-term stewardship.
Reston has preserved all of its streams, so they should be fine. What gives?
Preservation and conservation are two very different concepts. Reston's streams are in preserved corridors, but that doesn't stop the excessive flows that run off lawns, streets, driveways, and roofs during rainstorms. Reston was built before the era of modern stormwater management and, as such, allows runoff to flow unchecked into reservoirs like Lake Newport and Lake Audubon. These flows are the cause of Reston's stream degradation.
What's wrong with the streams the way they are?
Reston's streams are showing signs of stress from their urban surroundings. They are incising and their banks are eroding; they are depositing large amounts of sediment into Reston's ponds; and their ecological function has been severely impaired. These factors lead to problems such as disappearing land along the streams, drops in the water table (which affects surrounding forests and lawns), and an inability to sustain a diverse species population.
COULD BE UPDATED [use "does" rather than "will" because NVSRB is reality instead of planning] - How will stream restoration help our environment?
The restoration of Reston's streams will involve changes to the streams' pattern, profile, and dimension so that the streams can handle the urban hydrologic regime; the installation of natural, erosion-resistant material on the streambed and energy dissipation measures to help stop erosion on the stream banks due to high velocity flows; and the use of dense vegetation to provide bank stability and habitat for a wide range of species. Combined, these measures will help ensure that Reston's streams return to a natural, healthy, sustainable ecosystem.
Is there a difference between urban and rural streams?
There certainly is a difference between urban and rural streams. Urban streams are subject to the pressures of increased imperviousness in their watersheds, increased pollutant and nutrient loads, and often increased traffic when compared with their rural counterparts. Consequently, they are subject to much higher flow, and much higher bankfull flow, than rural streams. The urban stream responds to these changes through incision or sedimentation, algae blooms and eutrophication, and impaired ecological function. Stream restoration projects can help streams achieve a stable condition even under the pressures of urban life.
Given the site constraints of urban streams, reinforcement of the bed and banks will be necessary. Reinforcement includes rock structures, rock substrate, and heavy planting densities.
Can't we just dredge the sediment out of the ponds once in a while?
Dredging is an expensive, temporary, localized fix only; it doesn't address the root of the problem, which is increased sedimentation due to upstream erosion. Until upstream erosion is addressed (through streambank stabilization or changes in flow regime), Reston's streambanks will continue to slough into the ponds and necessitate periodic dredging.
Will you get rid of all the beavers?
It is not our intention to remove a particular species from the streams; rather, our goal is to create a balanced ecosystem. To do that requires allowing native species to thrive. If, however, an overabundance of a certain species (typically beaver or deer) threatens the health of the overall system, our certified Wildlife Biologist will humanely remove or relocate members of that species.
NEEDS UPDATE - Why is there so much algae in the streams? Is it detrimental?
Algae are present year-round in both Snakeden and The Glade. The types typically found are green algae (Division Chlorophyta) and golden algae, or diatoms (Division Chrysophyta). Having some algae in the streams is generally good for the health of the stream because the photosynthetic process releases oxygen into the water, which helps sustain other aquatic life. It provides food for grazing species and cover for other aquatic animals. However, having excess algae in streams can have a detrimental effect on the stream fauna because it can cover instream habitat and eventually cause die-offs of aquatic fauna.
Please click here for more information on algae in the streams. THIS GOES TO PDF SPECIFIC TO SNAKEDEN AND THE GLADE
What is the design process?
The design of a stream restoration project is a lengthy process that involves many players, including archeologists, survey crews, ecology specialists, regulatory specialists, engineers, and construction crews.
MAY NEED UPDATE - What are those little silver tags on all the trees?
We are tagging every tree over 4" in diameter (dbh- diameter at breast height) so that we have an accurate picture of the area we're working in and the constraints we need to account for in the design process. Tagging the trees allows us to design the project without worrying about running into snags in the field and helps us to avoid removing valuable trees. To date, we have tagged over 29,000 trees. UPDATE NUMBER?
The tags do not indicate which trees will need to be removed during construction.
Are you straightening the stream? If so, why?
The perception that we're removing meanders, or straightening the stream, is erroneous. The fact is that we are creating a stable meander pattern based on current hydrology. The impervious surfaces that were constructed in Reston over the past 40 years contribute more water, at a faster rate, than the original (smaller) meander radii could handle. The stream restoration project increases meander bend radii as necessary so that the stream can handle the velocity and volume of water it now conveys. (As an example, a sports car travelling at 30 miles per hour can take a much tighter turn than an SUV travelling at 60 miles per hour.)
In fact, the stream is currently in the process of widening itself in an effort to create a new floodplain and stable geometry for its current hydrologic situation. Left to adjust on its own over time, the stream would cut off the existing tight meanders as the erosional force of the water breaks through the weakened stream banks. (click on the image to the left for a larger view of this process.) Adjustment toward a stable geometry takes many decades, lowers both the stream and the water table, and causes loss of land, trees, and infrastructure in the process.
Will the pools create mosquito breeding habitat?
The restored stream follows a riffle-run-pool-glide pattern, which is seen in healthy streams in stream valleys similar to those found in Reston. Some of the pools do retain water between high storm flows; this is natural and provides habitat for many aquatic and riparian species. In fact, the existing streams also have standing pools of water between storm flows. Unlike the existing streams, however, healthy stream systems with floodplain connections also provide habitat for many mosquito and mosquito-larvae predators which keep the mosquitos in check.
According to the American Mosquito Control Association, the "bridge vector" (the main transmitter to humans) of the West Nile Virus in this area is the Culex pipiens. Culex pipiens is an urban species that generally prefers to breed in temporary standing water that is mildly to very polluted, such as tin cans, tires, tarps, and other human-made sources of standing water. While some females may breed in the restored streams, the percentage will not be higher than previously bred in the existing streams and will likely be significantly less than the percentage that breeds around homes and businesses.
What plants are you planting? Are they native to Reston?
We plant a diverse mix of native plants (including trees, shrubs, forbs, and grasses) along the stream banks and in the adjacent riparian areas. Once they start to grow, some of the of these may look "out of place" compared to the existing plants. This is both because much of the existing forest contains less diversity than our planting plan and because the dominant groundcover for the first year or two is comprised of fast-growing species used for erosion and sediment control (foxtail millet and annual rye). After one or two years, these fast-growing grasses will die off, and the perennial natives will take over. All of the species being planted are native to the Northern Virginia area, and the increased diversity of native plant species offered by the stream restoration plan will benefit all species of wildlife that call Reston home.
Why are you planting seedlings instead of larger ball-and-burlap stock? Won't they take a long time to grow?
Based on our past experience, and as recommended by the Virginia Department of Forestry, seedlings and smaller container-grown stock are preferable to ball-and-burlap trees for reforestation projects for three reasons:
First, ball-and-burlap stock must be watered for the first year or so to ensure survival; this encourages the growth of invasives. We've achieved much better success in natural settings by overplanting and letting the strong survive.
Second, ball-and-burlap stock spends its first few years after transplant regrowing root mass that was removed during the transplant process. Seedlings and container-grown stock, which are transplanted with their entire root system intact and can spend all their energy on growth, typically catch up with their ball-and-burlap counterparts in both height and diameter within several years.
Third, seedlings and container-grown plants send out more roots more quickly than ball-and-burlap trees. These roots interweave with each other along the stream bank and help to lock the soil in place. Root mass is one of the factors leading to stream stability, and the faster-rooting seedlings and container-grown trees contribute to streambank stability much sooner than ball-and-burlap trees.
Why aren't you using tree tubes to help the new trees survive?
We choose not to use tree tubes for many reasons:
First, in floodplain areas, using tree tubes can actually cause greater seedling mortality than not using them. In large storm flows, the tubes can get knocked over by the force of the water. When this happens, the tube pulls the seedling with it, ripping its roots out of the ground and killing it.
Second, in our experience, tree tubes often do not decompose as quickly as the literature would suggest. In past projects, we have had to return to a site several years after planting to cut the tree tubes away from trees that grew more rapidly than their tree tubes decomposed.
Third, because tree tubes are tall and effectively block wind, seedlings grown in them tend to grow tall but weak. Allowing the seedlings to grow unhindered but unaided results in stouter, more vigorous trees.
Finally, we find seedlings and young trees to be more pleasing to the eye than a landscape dotted with plastic tubes.
In lieu of tree tubes, we combat deer browse by overplanting. This allows natural selection to dominate, and the strongest seedlings grow to become vigorous, healthy trees. We have used this method on nearly all of our wetland and stream projects (approximately 900 acres of created/restored wetlands and 140,000 linear feet of restored streams) with great success.
Aren't you removing existing streamside habitat?
Reconfiguration of the existing eroded and unstable stream banks does require grading of those areas. However, while it may seem logical that scour holes in the existing stream banks would provide good cover for animals such as foxes and raccoons, this isn't actually the case. Because the water in the streams is so "flashy" (i.e., it rises very quickly after a storm), these streambank features flood regularly and would be very dangerous places for animals to hide, sleep, or raise their young. Additionally, bank failures in degraded systems are commonplace, which further impacts any potential habitat.
Similarly, overhanging root masses may seem like ideal bat habitat since they have so many nooks and crannies for roosting. However, bats initiate flight by dropping several feet from their roost to begin their swooping flight pattern, and there simply isn't enough depth below the root masses for them to do so, especially if there is any amount of water in the stream. Like other animals, they would also drown as the water in the stream rises after a storm.
Contrary to both of these misconceptions, the stream restoration project will benefit wildlife by providing long-term bank stability, connection to the adjacent floodplain, and fully-vegetated banks consisting of native riparian plants. This will provide quality habitat for many species, will allow animals to access the streams for water, and will help restore health to the entire riparian ecosystem.
Will the stream restoration cause my basement to flood?
During the design process, the 100-year floodplain for each stream is modeled under existing and proposed conditions to verify that the streams will have no more flooding potential than existed previously. In short, the restored streams will not flood anyone's basements any more than the existing streams do.
Why have some of the bridges moved?
Reston's sanitary sewer network lies beneath its streams and woods, and some of the existing bridges lie partially or completely within sanitary easements. This is not an ideal situation (and is also not allowed by the language of the sanitary easements) because the bridge foundations can cause undue pressure on the sanitary pipes, resulting in breakage. Additionally, the bridges could be removed or damaged when maintenance to the sewers is performed. With the restoration, all bridges have been moved outside of the sanitary easements and have been designed to be perpendicular to the streams (to minimize their length). Because of this, some of the bridges may have moved slightly- usually on the order of only a few feet.
How will the restoration project affect deer and other species?
During construction, some animals will be temporarily displaced by equipment noise and proximity. However, the animals that call Reston home are accustomed to living in an urban area and are well-adapted to human activity and proximity. The animals we encounter typically move to the undisturbed areas adjacent to the stream for the duration of construction and return once the equipment moves downstream. Some, like the fox at the right, don't even wait for construction to end before returning to check out the new streams. Click here to see photos of some of the wildlife we've encountered in the restored streams.
Immediately following construction, animals such as deer and foxes will again be able to access the streams for water; previously, access to the unrestored streams was limited by the tall, vertical banks. After construction is completed, the restoration project will benefit a wide variety of species. Owls and hawks will hunt in the areas of new growth, where they will be able to easily see their prey.
When the new plantings mature, the increased diversity along the streams will provide food and shelter for a wide range of species; volunteers from these plants and trees will also begin to diversify the adjacent woodlands, resulting in a healthier overall stream valley.
NEEDS UPDATE - THE GLADE IS REFERENCED AT THE END - Do you have to remove trees? If so, how do you assess the "value" of one tree over another?
One of the key reasons the streams are degraded is that they are simply too small or too incised to convey the flows generated by Reston's impervious areas. The stream restoration project will create stable dimensions for the streams; in some cases, the stable stream width is larger than the width of the degraded stream. In nearly every case, the stream is incised and the banks need to be graded to a flatter, more stable slope that can support vegetative growth. Either case requires that certain trees currently growing along the stream be removed. In some areas, both the cross-sectional dimension and the channel pattern (the meander bend radii) are too small to carry the current flows; in these cases, we both enlarge the stream for the new flow regime and increase the meander radii. (See above for further discussion on meander bends.) This again requires that trees be removed for the new stream channel.
In some areas, it may look like we've removed more trees than necessary. However, many times these are areas where the old channel was filled-in (due to a tight meander bend or to protect infrastructure) and the new channel was constructed beside the old. When completed, this gives the appearance of a larger-than-necessary "cleared area" when there were actually no trees there to begin with. Rest assured that the grasses, forbs, shrubs, and trees that have been planted on the old channel will soon grow and fill the visual gap.
In cases where the stream width must be increased and there is a tree on either side of the existing stream, we need to make the choice of which tree to remove and which tree to save. We make this choice on a case-by-case basis and evaluate several factors, including species, habitat value, size, health, and estimated life span. One factor we DO NOT take into consideration when choosing which trees to remove is any monetary value associated with the sale of the wood from trees. In fact, in the Glade watershed, all removed trees will be either used as habitat in the restored channels or cut, stacked, and given to Reston residents as firewood.
What is the "stockpile area" used for?
The stockpile areas on each plan are essential to the project. There must be a place immediately adjacent to the project to have materials delivered by on-road trucks. Specialized, low-impact equipment then distributes the materials from the stockpile areas to the streams where they will be used to restore and stabilize the channels. Every effort is made to make these areas as small as possible to disturb as few trees as we can. After construction, the stockpile areas are seeded, mulched, and planted in the same manner as the rest of the project. (See above for further discussion on planting.)
NEEDS UPDATE [references older work sections] - Why have I seen a few white PVC pipes scattered randomly throughout the streams?
The white PVC pipes are part of a stream gauge monitoring network; fourteen gauges are located throughout the Snakeden Branch, Glade, and Colvin Run watersheds. Each pipe contains a pressure sensor that is located at the stream thalweg. The sensors measure the water depth in the stream, which we then use to determine the stream's flow rate (volume of water per unit time, typically "cubic feet per second"). Stream flow monitoring is an important part of the stream restoration process, especially in areas like Reston that have experienced a change in watershed hydrology through urbanization. The collected stream flow data has been used to design a “low storm flow” channel to provide improved habitat for aquatic life, and continued data collection will play an important role in advancing the science of stream restoration. Stream flow monitoring for the Northern Virginia Stream Restoration Bank started in 2003 and will continue through the project's 10-year monitoring and maintenance period.
The stream gauge monitoring network is constantly collecting data. It is important that the stream gauges are accurately calibrated during installation and that they remain fixed in place during the data collection period. This is often difficult when collecting data in the natural environment, especially in urban areas. If you notice a stream gauge that has been damaged or tampered with, please contact WSSI.
What is the basis for the spacing on the construction access “cut-ins,” and why can’t the distance between them be increased?
The “cut-ins” provide access to the stream channel from the main access path, as depicted in the figure to the right. (Click on the image for a larger view.) Locations are selected based on two basic criteria: 1) fewest number of trees and 2) a spacing of approximately 100 ft (on average – this distance varies somewhat depending on available open areas). This interval is the maximum practical spacing that enables the work to be performed, for several reasons:
Given the very tight limits of clearing along the stream channel, there is virtually no room along the banks to allow tracked carriers to travel up and downstream to deliver materials to the excavator performing the restoration work in the channel.
As a result, the channel itself must essentially be used as the access corridor between the cut-in locations. The access within the channel itself should be limited as much as possible to minimize the length of disturbed channel that must be temporarily stabilized. Although a “pump-around” system is used on a daily basis, whereby the work is conducted in a relatively dry condition (i.e. no flowing water), the portion of the disturbed channel used for access must be stabilized at the end of each day since it is still an active watercourse. Otherwise, pumps would need to be manned and running 24/7 – which still would not be sufficient during rain events. By limiting the length of the access in the channel to approximately 100 ft, this keeps the length of disturbed channel that must be temporarily stabilized to an acceptable minimum. In addition, construction crews have been averaging approximately 100 ft per week – so the 100 ft spacing allows for any particular section to be completely stabilized in the space of a work week (minimizing weekend exposure).
The very tight limits of clearing along the channel eliminate any room for temporary placement of materials as the work is progressing (both excavated material, including the existing stream-bed gravel to be placed back in the stream as desired by the citizens, as well rock materials being brought in). Thus, smaller open areas (no trees) along the cut-ins need to be used for temporary storage (as shown in the figure). Given that each area is very small, the available number of locations must be maximized in order for the work to progress. Again, the 100 ft spacing is the maximum practical to provide for reasonable access to these small storage areas.
Since we can’t store material in and use the narrow stream for access at the same time, eliminating or significantly changing the spacing of the cut-ins is not reasonable or practicable.
Alternative to the Cut-Ins
There is one alternative that could significantly reduce the number of cut-in locations – increase the limits of clearing by about 15 ft on one stream bank to allow the access to be located outside the stream channel. This could also provide the necessary small storage areas directly adjacent to the channel. However, the reason this option is not being used is that it would result in significantly more tree loss. While the cut-in locations have been selected to avoid as many trees as possible, a wholesale expansion of the streamside limits of clearing would not provide the same flexibility.
Lastly, concern has been expressed regarding the disturbance to smaller trees and herbaceous plant materials in the cut-in locations. While larger trees have been avoided, clearly other smaller plant materials will be impacted. However, the overall impact to this forest layer will minimal. We are employing the use of “deck-mats” (wooden structures that will form the road bed – their use distributes loads to reduce soil compaction and significantly reduces damage to the soil surface). Once the use of a particular cut-in is complete, the mats will be picked up and moved to the next one and the area restored. Given the relatively short duration during which the cut-in will be used, underlying plant materials will be able to recover quickly from the root stock and soil seed bank. It is our estimation that within 1 to 2 growing seasons, it will be difficult to tell where the cut-ins were actually located.