Here is another Prince George's county Manual. This is the design manual
A HREF = "http://www.princegeorgescountymd.gov/Government/AgencyIndex/DER/ESG/Bioretention/pdf/bioretention_design_manual.pdf DRIVEWAYS:: Driveway areas that serve 2 way traffic are 18' wide. Driveways should be done in permeable Macadam. The mix for permeable macadam can be found at :: http://www.snh.gov.uk/publications/on-line/advisorynotes/5/5.htm These surfaces have infiltration rates of more than 1 mm/s when new, (2.36"/min) although this can deteriorate to more than 0.2 mm/s after 5 years as silts accumulate in the surface layers (Maskell et al, 1992) from http://www7.caret.cam.ac.uk/guide_suds.htm Macadam will last 7 - 10 years before it needs any maintenance. Asphalt needs to be re-sealed every other year. This solution will result in savings in association fees, look a lot nicer than an asphalt driveway, is permeable, maintenance free, doesn't cost any more and comes in a variety of colors. SIDEWALKS:: Sidewalks done in permeable cement. The mix and method can be found on King County's web site. http://74.125.95.132/search?q=cache:JKP9aUnlNUQJ:www.kingcounty.gov/transportation/kcdot/Roads/Environment/LowImpactDevelopment_MilitaryRd/~/media/transportation/kcdot/roads/engineering/documents/militarys272/J970496.ashx+permeable+portland+cement&cd=10&hl=en&ct=clnk&gl=us ROOF DRAINAGE:: Impervious rainfall footprint of 1 unit is 1166 SF. 1" of rain produces 97.16 CF of water (723 gallons). Capture Roof Runoff in a vegetative biorentention and infiltration swale system located 15' away from the foundation. This is not a conveyence system. It is not a grass swale or a rain garden[1]. It is an extremely high absorption and infiltration forest ecosystem bioswale. To avoid deep cuts into the topography, keep the swale aligned and parallel to the long side of the units, ie. along the driveways or in the same alignment. according to the epa, vegetative swale gives highest reduction in volume over time - -209%. http://iaspub.epa.gov/urbanbmp/index.jsp?action=bmp_result Its is also the cheapest solution as well as the best BMP solution for contaminant removal and the best LID solution. http://www.epa.gov/owm/mtb/vegswale.pdf Plant swales with commercial mix for this type of swale to get it started: http://www.agrecol.com/cms/seed_mixes_page12.aspx or make your own. Most of the native plants on the following swale plant list are also native to MA. http://docs.google.com/viewer?a=v&q=cache:h3fSydJWN9AJ:www.spokane-county.wsu.edu/spokane/eastside/Swale%2520Project/swaleplantlist.pdf+infiltration+swale&hl=en&gl=us&sig=AHIEtbTVRXZpaY8fcAGDs0ll8e3_J71eiA These swales are not maintained unlike other solutions. Native trees and shrubs will volunteer and the foliage in the swale will change over time as the swale matures. The more mature the swale, the better the absorption, infiltration and contaminant removal. Most of the roof runoff falls to a downspout right near the front door. The remainder of the runoff ends up in a downspout in the patio area. Water from the downspouts is directed to the swale using a stone path Forest ecosystem swales. When a swale is designed as a biofiltration system instead of a conveyence system, the soil absorption is increased by 75%. These swales should never be interferred with. http://www.deq.state.id.us/WATER/data_reports/storm_water/catalog/sec_3/bmps/33.pdf wucols - evapotranspiration per plant saturated sandy loam has a perc rate or hydraulic conductivity of about 180 mm/hr http://www.derwentestuary.org.au/file.php?id=213 that is about 7 inches/hour Notes[1] ROAD DRAINAGE:: Road Drainage. Every LF of road 26' wide of pavement will run off 2.16 CF of water per 1" of rainfall. (26' * 1" * 1'/12"). The uphill side of the road has a sidewalk, the downhill side of the road has a swale. Same swale design as for roof runoff. IMPERVIOUS SURFACE RUNOFF CONTAINMENT DIAGRAM:
LAWNS::
Grass Lawns. If lawn areas are traditional grass mix, they might need to be mowed, irrigated and fed. If there is any irrigation it will effect the size of the community well. A selection of native grasses and legumes will never need to be fed or irrigated but will need to be mowed.
Alternative Lawns. A low growing ground cover type wildflower/herb mix can be used instead of a grass mix. A lawn can consist of all native wild plants, each with one or more spp. specific to the Worcester area, such as violets, violet oxalis (sorrel), dandelion, strawberries, plantain, creeping phlox, moss phlox, buffalo grass, spring beauty, various low growing sedges, kinnekinack, silver cinquefoil, star eyed grasses, blue eyed grass, gamma and wild ginger for instance. The plants in the list above all pretty much grow 6" or less. Such a lawn would be in bloom for much of the growing season and would never require mowing, seeding or watering and therefore, no effect on the community well or on the pollution load of the project.
The cost of an alternative lawn. Many of the wildflower seeds are very small. A plant may have 25k seeds per oz and the cost may be $100/oz. However, if plant spacing is recommended at no more than 1 plant per SF, then the 25k seeds will do 25k SF of alternative lawn. A wildflower or wild herb lawn could end up being very cost effective. Some of the above plants don't come as seeds, rather runners, like strawberries. Many of the plants on the above list are also invasive (not all) which means the lawn will fill in and stay filled in.
Prairie Moon nursery specializes in this sort of thing and can offer instructions, advice and supply seed.
Alternative lawns may need to be mowed occassionally during the first 3 years until they are established.
RIPERIAN BUFFER::
Riperian Buffers. Forest ecotypes are the best at absorbing any runoff. The bottom land acreage between the subdivision and singletary, as well as the 2 large side yards should be planted with a selection of hardwoods. These trees should be no more than 1 year old and somewhere between 12" and 18" high. Older, taller, thicker stemmed trees (ie. street trees conforming to zoning) are supposed to have a large root system and a large crown for their age. They have been constantly pruned. The constant pruning of the crown and the roots gives these trees enough stress to last for a long time. They do not recover during their juvenile growth spurt years and therefore, miss that. This is documented by the National Forestry Service. A 5 year old tree that has been pruned will grow very slowly and will not recover for years. By then, the juvenile growth spurt period has genetically completed and the tree enters a period of slower growth. A tree that has not been pruned and stressed will be much taller, have a wider stem and be much healthier at the end of the same period of time. The riperian buffer trees will outgrow the street trees in height and weight over the same period of time.
Assume the average mature hardwood tree in a final forest setting takes up at least 24x24 in area (576 SF). The bottom land along Singletary is about 59,500 SF and will require about 103 trees. The west side is about 70' wide by 627' long for 43890 SF and will require 76 trees. The east side is also 70' wide and about 480' long, which will require 58 trees. The total number of trees to make a riperian buffer and landscape the lower half of the land on the perimeter is 313 trees. An area should be cleared of competition before planting each tree. To insure their greatest potential of survival it is best not to mow, fertilize or water once they are planted as those things may confuse a native tree. Once the trees are established and growing, they will shade out and kill of the existing understory and be replaced by native volunteer forest understory plants. These trees (depending on selection) should exceed 20' in height in the 4th year.
Native hardwood trees of various kinds can be purchased at a young age and no more than 18" in height for about $6/tree. The more trees you order the lower the price per tree. If a local nursery cannot be found to supply native hardwoods, you can get them mail order from Porcupine Hollow Farms, Michigan.
OPEN SPACE::
Open Space. The community well area. Use as a wildlife preserve. Over seed with native wild prairie flowers - many tall growing. Mowed foot paths on the perimeter, possibly one across the middle. Access should be prohibited outside of the mowed paths to avoid damaging the plant life. Cost of wildflower seed varies and sometimes its better to put together a mix yourself. Echinacea, black eyed susan, various sunflowers and golden rods for example, are not expensive and readily available at all times. That area is less than 5 acres and will probably won't need that much seed. Native seeds may take more than 1 year to germinate. Once they start growing and reproducing, they will keep reseeding the area. Tall flower plants quickly shade out the existing foliage and kill it off. If the cost of seed is prohibitive, then a smaller amount of seed can be used and let the plants take over on their own. A company that specializes in this sort of conversion is Prairie Moon Nursery.
RECREATION ::
Recreational Amenities. A dirt trail in the forested buffer areas. Nearly all Mi. forest trails, in all park types are raw forest floor. They are not mowed, chipped or paved or anything. Those paths can be tied into the mowed paths in the open space area which is reserved as a wildlife habitat. The total distance is over 3,000 LF of paths.
Prviate Garden space is shown next to the clubhouse. It is assumed that at least some, limited irrigation may be needed for the hot summer months only, in the event of drought. That figure may need to be added to the community well. Alternatively, rain barrels can be used.
FOUNDATION PLANTINGS::
There is a 6' wide planting strip on the entire perimeter of the building shown in the elevations. It is assumed this is sloped at 1" per foot away from the building, covered with plastic and used as a planting strip.
The 2 exposed sides of the patio can be planted with shrubs, deciduous or evergreen. Some native choices are dogwoods, viburnums and Juniper. A low growing tree can be planted in the exposed corner to allow for some shade and protection from the elements. A high bush cranberry, squashberry or mountain ash are examples that would have a lot of winter interest and be the correct size.
The LR windows can be flanked with deciduous native shrubs that have winter interest such as winterberry or bittersweet. Below the window can also be planted with native shrubs or wildflowers.
The area beneath the DR window can be a more formal garden.
The sides of the building can be planted with low growing native junipers as evergreens or from a wide selection of low growing deciduous shrubs that also have winter interest.
NOTES::
[1] Simplified Darcy's equation indicates a rain garden of approx. 60 SF per 1" of rainfall with infiltration rates of 6"/day,
which is moderately clayey soil, for 1,200 SF impervious surface. A rain garden is typically only 3" deep.
http://www.socwa.org/nature/PDF/RainGardenSizingforHomeowners-%20Report.pdf
A swale 4x deeper, reduces to 15 SF. If the swale is 6' wide then every 2.5' of swale will handle the 1" rainfall event at the given infiltration rates. To accommodate a 5" rainfall event requires 12.5 LF of swale. Most precipitation events are 1" or less.
The swale should never have standing water in it if it is planted properly and not disturbed. After the initial seeding, no maintenance will cause the proper plants to volunteer in a normal succession.
Infiltration Rate. Qmax = k * L * Wbase * (hmax + d) / d)
k is the hydraulic conductivity of the soil filter in m/s
W base is the base widtho of the ponded cross section bove the soil filter (m)
L is the length of the bioretation zone (m)
hmax iis the depth of pondage above the soil filter (m)
d is the depth of the filter media.
A mature tree takes up 80 gallons per day on the average. The actual amount depends on many factors such as wind, temperature, insolation, humidity, soil moisture and more.
An acre of corn takes up 4,000 gallons of water per day.
Rain gardens are typically designed to capture the first 1/2" of rainfall from a rooftop or driveway. A rain garden is deep enough to pool 3" of water. Rain gardens are designed to overflow in heavier rains and should be 15' away from basement foundations. The basic perc test for a rain garden is a hole 18" deep in the native soil. The hole is filled with water and allowed to drain. The hole is filled a second time. If the water leaves within 24 hours then the site and the soil is suitable for a rain garden without any soil amendments. Native plants are adapted to the native soils not to nursery mixes or amendment mixes. If the soil is amended the rain garden plants are likely to die in a time of drought or will require irrigation.
Rain gardens are very high maintenance and may require irrigation in times of drought. Mulch is added as organic matter to act as a sponge. This is added annually. In contrast, the swale design relies on tree leaf fall and other debris to get its organic matter to serve the same purpose. . http://www.socwa.org/nature/PDF/RainGardenMaintReport1-08.pdf