From: Gutzler, Emma B. [Emma.Gutzler@fairfaxcounty.gov]
Sent: Wednesday, August 01, 2012 11:37 AM
To: Gayle Abbott (firstname.lastname@example.org)
Cc: Rose, Fred; Curtis, Shannon
Subject: Piney Branch - Site Walk Summary
It was a pleasure meeting with you and the board on June 27th and walking the stream valley as it flows through your community. This is to serve as a summary of key points we discussed in the field. Please share this with the other HOA board members. If you have any questions on anything or if I missed something we discussed, please let me know.
It is really great to see the interest your community has in being stewards of the stream and seeing it as a natural asset. We commend you on the stream improvements you have already implemented this year, such as the establishment of a no-mow along the small tributary, and on your ongoing efforts to learn more about how you can better care for the stream. Let us know if we can be of further assistance to you as you continue forward.
Large Woody Debris Management
Our understanding is that a large portion of the grant funds you were awarded, as well as the community match, was going to be used to remove large woody debris from the channel.
Large woody debris (LWD) is a valuable though often misunderstood ecological component of a stream. LWD enhances available instream habitat for fish and insects, provides a valuable surface for colonization of periphyton and microscopic algae which form the basis of the aquatic food chain, can provide grade control for the stream bed, and can protect against bank erosion. However, LWD also poses concerns in our urban and suburban environments. LWD, depending on its orientation in the stream, can direct and accelerate flows causing streambank erosion. It can also potentially block the stream channel, or nearby culverts and bridge openings causing undesired effects. While these concerns are most certainly valid, thought is needed prior to removing LWD from the system so as to keep us from clearing all wood from our streams.
Below are some guidelines for when LWD should be left in place, at least in most circumstances:
· Rootwads and stumps. These are usually stable and provide great habitat.
· LWD that is embedded (i.e., buried in sediment) in the stream. In most cases embedded LWD is providing grade control. Removal may create a knick point in the elevation of the bed and result in channel incision and bank erosion.
· LWD that is positioned such that is protecting the bank from scour. An example of this would be a log lying along the toe of the bank parallel to flow, or a log extending from the bank and angled upstream so that it concentrates flow towards the center of the channel and away from the bank.
· LWD not occupying more than 10% of the channel cross sectional area, not directing flows such that it endangers nearby structures, and not situated such that it is collecting additional LWD.
You would want to consider repositioning, anchoring, clearing out the center so water can pass, or completely removing from the channel LWD that is:
· Within 100’ of a culvert;
· Directing flows such that it is endangering a road, structure, or sewer line;
· Directing flows into the stream bank and causing excessive bank erosion;
· A LWD jam that occupies more than 10% of the channel’s bankfull cross sectional area (note that bankfull height is not average flow height but is based on a storm flow that occurs with some regularity, approximately once a year) ; or
· A LWD jam that acts as a dam (i.e., not allowing flow to pass).
Invasive Plant Control
Unfortunately invasive, non-native plants are everywhere in Fairfax County. They have escaped cultivation, colonized our stream valleys and natural areas, and can dominate the landscape. These plants often form large stands that can outcompete native plant varieties. Some non-native invasives change the chemistry of the soil, some climb native trees and shrubs, and most form dense stands which prevent other plants from growing alongside of them. Many of the non-native invasive plants common in this area are shade intolerant, meaning that they thrive in sunny, open areas (such as woodland edges and canopy gaps within our woodlands).
Controlling non-native invasive species requires persistence and dedication. To maximize efficiency control methods and timing should be selected based on the species. The first priority in terms of non-native invasive plants needs to be to keep them from establishing in new areas. Regularly monitor your newly established no-mow zones and pull any unwanted plants you see. Controlling them early on will save you a lot of work and time later. In addition to monitoring and hand pulling new establishments, you may want to have a “free the trees” workday and concentrate on cutting and removing vines that are endangering trees. If you decide to target community efforts on an area, we encourage you to select a small and manageable area. After you have invasives in that area controlled, you will likely want to plant natives to discourage re-colonization of invasive species. At that point you can then shift your invasive control efforts to another area.
Chemical measures can also be used to control non-native invasive species. To minimize unintended ecological impacts and to select the correct chemical, application method, and application timing, you should consult with a licensed applicator with experience working near aquatic habitats.
Some of the invasives present at your site include: multi-flora rose, wild grape, mile-a-minute weed, various honey suckle species, autumn olive, and privet. Information on plant identification and species specific control methods and timing can be found online at: http://www.dcnr.state.pa.us/forestry/invasivetutorial/List.htm.
You mentioned an effort to control ornamental ivy species (Boston and/or English ivy) and poison ivy in the upland wooded areas of the park. Poison ivy is a native plant, and the birds love its red berries. We recommend you control poison ivy along your paths for the safety of your park users but allow it to grow in the more natural woodland areas.
As you educate your community on non-native invasives, remind them that many of the non-native invasives we are “fighting” in our natural areas are escapees from our residential landscapes. Unfortunately some of these can still be purchased at garden centers today, such as pachysandra, English ivy, wisteria, burning bush or winged euonymus, privet, and Japanese barberry, just to name a few. Encourage them to avoid these plants and to instead select native trees, shrubs, ferns, and flowers. In addition to providing habitat to birds, butterflies, mammals and other animals, native plants provide invaluable and necessary habitat and food (which non-native invasives cannot) for insects and butterfly larvae.
Riparian Buffers: No-Mow Zones, Native Plantings, and Tree Care
A riparian buffer is simply a vegetated area adjacent to a stream. These buffers provide many benefits to the stream and the creatures that depend on the stream. Plants help to slow bank erosion as their roots anchor the soil. They encourage infiltration of water into the soil, filter runoff and improve water quality, and slow stream flow due to their roughness. Large trees along the stream also provide shade helping to keep water temperatures cooler on hot summer days; this benefits the creature and water quality. Furthermore buffer plants provide important habitat and food for aquatic and terrestrial wildlife. The wider, denser, and more continuous your buffer the more ecological benefits it will provide.
One way to establish a riparian buffer is to create a no-mow zone, as you have done along the small tributary. Keep an eye on these areas for invasive species and try to control them immediately. If you desire to keep more of a meadow feel in this area, consider “mowing” twice annually (April/May, and September/October). This will help to control weed species and prevent trees and shrubs from establishing. Note that the area should be mowed 4-6” in height and should be done either with a weed-eater or a flail type mower. A lawn mower will mow too close and encourage weedy grass species.
Another way to establish a riparian buffer is to plant the area with native species. Native grass and wildflower seed can be purchased and sown in bare areas. (One supplier, with a helpful website, is Ernst Conservation Seed (http://www.ernstseed.com). They have various premixed seed mixes, including mixes best suited for riparian sites.) Native tree and shrub container stock can also be purchased and planted. Early spring and fall are ideal times to organize a planting event. Planting plans can be developed to provide ecological benefits while also providing stream access points and aesthetics to your park. Some beautiful native plants you may want to consider are listed below. Remember when selecting plants to consider moisture and light requirements, along with mature height. (More information on characteristics and growing conditions for these species and others native to the Chesapeake Bay Watershed can be found online in the “plant information pages” of the US Fish and Wildlife Service’s Native Plants for Wildlife Habitat and Conservation Landscaping.)
River birch (Betula nigra)
Red maple (Acer rubrum)
American sycamore (Platanus occidentalis)
Black gum (Nyssa sylvatica)
Pin oak (Quercus palustris)
Willow species (Salix sps.)
Tulip poplar (Liriodendron tulipifera)
Flowering dogwood (Cornus florida)
Redbud (Cercis canadensis)
Shadbush (Amelanchier canadensis)
Sassafras (Sassafraas albidum)
American elderberry (Sambucus canadensis)
Winterberry holly (Ilex verticillata)
Red twig dogwood (Cornus stolonifera)
Silky dogwood (Cornus amomum)
Virginia sweetspire (Itea virginica)
Arrowwood (Viburnum dentatum)
Paw-paw (Asimina triloba)
During our walk we identified several areas along the left bank (looking downstream) where the buffer could be expanded or enhanced. Several of these were along outside bends. A combination of establishing a no-mow zone of 10+ feet and planting native species will add value to the stream and help slow erosion. Some of these areas may fall within the sanitary sewer line easement. Before planting in these areas contact the Fairfax County Wastewater Collection Division (703.324.5030) to coordinate planting locations and species.
As is common in our urban stream valleys, there are a number of undercut and leaning trees along the streambank. We encourage you to monitor these trees following storm events for any changes. There were several trees we discussed having removed before they fall naturally. When trees fall naturally the root ball often disrupts the streambank causing a portion of the bank to fail. When proactively removing the tree, the tree stump should be left so as to continue providing structure and roughness to the bank. There were other trees along the stream where we discussed pruning the trees in such a way to reduce the weight and discourage the tree from falling. A certified arborist can further assist you in identifying what trees should be pruned or removed. They will also be able to properly prune the trees such as to preserve the health of the tree.
We look forward to hearing about the actions you decide to take to improve your section of Piney Branch and the Difficult Run watershed. Again, please contact us if you have any questions or if we can be of further assistance as you move forward with your project.
Emma B.L. Gutzler
Stormwater Planning Division, Watershed Planning & Assessment Branch
Department of Public Works & Environmental Services
12000 Government Center Pkwy., Ste. 449, Fairfax VA 22035
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