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Public Site Crenshaw High School, Los Angeles, CA TEAM MEMBERS
Landscape Architecture Graduate Students:
PROTOTYPE This is a typical public school site with typically high graywater discharge rates, large amounts of roof and impervious paved areas, large recreation fields that require irrigation, and soils with moderately slow percolation rates. SITE PROFILE Crenshaw High School is located at 5010 11th Avenue in the Crenshaw district of southwest Los Angeles, a middle-income area consisting of single-family homes built in the 1930s. The nearby commercial district on Crenshaw Boulevard is home to many small neighborhood businesses. Leimert Park, another adjacent commercial area, is being developed as a local arts and entertainment district, with coffee houses, small restaurants, and music venues. The school currently has a student body of 2,700. Over 80% of the students are African American and 18% are Latin American. Crenshaw High School houses one of only two programs in the Los Angeles Unified School District for gifted students. The school is also known for its award-winning athletic programs and its internationally recognized choir. The highly successful and nationally acknowledged 'Food from the Hood' college scholarship program began at Crenshaw High School. The program teaches students how to run a business "from the ground up", with the proceeds from the 0.25-acre organic herb and vegetable garden being sold for profit or donated to neighborhood families. The 25-acre site includes five separate buildings, all less than 30 years old. The remainder of the site is dedicated to athletic fields and parking. The underlying soils are of the Chino association. These soils are over 60 inches deep, are somewhat poorly drained, and have moderately slow permeability. The seasonal high water table can be within 3 to 5 feet of the surface. SITE DESIGN PROPOSALS Site design and remediation proposals for this site easily exceed the performance objectives set out in the TREES project (refer to the introduction section of this document). For example, there is enough land at the Crenshaw High School site to detain or slow stormwater for rains of up to 10 inches. In fact, the site has enough capacity to filter the first-flush rain (0.25 inches) that falls on it as well as on an additional 25 acres of surrounding paved streets. Stormwater falling on the site is cleaned in a variety of ways: by porous parking areas, by soil and shade trees, and by lengthy vegetated swales (discussed below). The underlying strategy of the design proposals is to reduce the amount of domestic water that is imported to the site; to re-use imported water on the site for irrigation; and-in an attractive, useful, and educational way-to hold, filter, and re-use stormwater that falls on the site and on nearby streets. All of the buildings and their uses remain unchanged. The following specific remediation measures are proposed by the charrette team in order to meet the environmental performance objectives of the TREES project. These measures can be applied to similar school sites throughout the region or they can be applied to future sites. Roof Cisterns and Planters Downspouts intercept all roof drainage and channel it into raised planters that are located on the ground along the face of the buildings. The planters are designed to filter and retain all roof water generated by the average local storm. Excess water is held inside the planters (below the planting soil) for later irrigation use. This simple above grade system is easy to install and can hold approximately 4 acre-feet per year of stormwater (20% of the total requirement for irrigation water per year). Playfield Cisterns The design team proposed that a system of pre-cast concrete pipe storage basins, or cisterns, be located beneath the turf playfields on the Crenshaw High School site. These basins store rain water and graywater to be used for the property's annual irrigation needs. Using local stormwater management statistics and actual annual domestic water-use figures provided by the school, the design team estimated that, using standard irrigation equipment, a combination of stormwater and recycled graywater from the gymnasium showers can be used to supply all of the 25 acre property's irrigation needs during all 12 months of the year. The team reached this conclusion after assuming that water use for showers would be decreased by 70% through the installation of low-flow shower heads which could be installed immediately. Approximately 33 acre-feet of rain water falls on the 25-acre site during an average year. Based on a water budget for the average year, the team provided playfield cisterns, with a capacity of approximately 20 acre-feet, to hold the graywater from the school for immediate re-application onto playfields (fields must be irrigated even in winter when evapotranspiration is still between 2 and 4 inches per month) and for captured stormwater that can be held for much longer periods of time. These 20 acre-feet would provide enough water to satisfy the landscape irrigation demands during the dry months. Gym Shower Graywater System Current domestic water use at the school is estimated to be 25 gallons per day per student. With a total of 2,700 students, the total domestic water needs are equal to 54 acre-feet per year. It is assumed that the gymnasium showers account for 50% of the domestic water use. With the installation of standard low-flow shower heads, the amount of water used in the showers would be reduced by 70%. The total amount of graywater produced by the showers and reclaimed for irrigation use is 9 acre-feet per year. Depending on the demand for irrigation water at the time of discharge, this graywater will either be used directly for irrigation or stored in the playfield cisterns for later use. Measures may be needed to prevent bacteria build-up in these cisterns, where water-use rates, water-storage duration, and the proportion of graywater to stormwater may vary widely. Porous Parking Area with Shade Trees The design team proposed converting the existing under-used parking areas into groves of large canopy trees that would delineate parking aisles and shade the surrounding area. These shade trees help to reduce ambient air temperature on the site, absorb significant amounts of carbon dioxide, and hold excess stormwater run off. The team suggested that parking stalls slated to remain should be covered with a pervious crushed stone. The porous stone surface would allow stormwater and auto-related contaminants to be absorbed and trapped in the soils below at safe concentrations. Vegetated Swales Swales are shallow drainage channels that direct the flow of stormwater on the surface of the ground. Vegetated swales are planted with trees, shrubs, and grasses to help slow run off and to filter water-borne pollution. A vegetated swale slows the flow of rain water so that it can be absorbed directly into the soil, thus reducing storm impacts. Vegetated swales filter a portion of water-borne pollution before it can contaminate water downstream, leaving grease, oil, and other potential contaminants trapped in its soil and vegetation at harmless concentrations. The vegetative swale by the softball field also captures and filters the first- flush rains from adjacent streets. The rain water from the softball field's terraced land area is channelled down the broad vegetative swale that cuts through the paved basketball area. This swale brings the water to the playfield cisterns under the football field at the lowest elevation of the site. This swale is 20 feet wide with a 2% slope at its centerline. The drainage path is lined with 100-pound washed river stones. Trees, grasses, and shrubs are planted between the stones to further slow the water in the swale and to increase on-site stormwater retention rates. The vegetated swale proposed for the basketball court area requires the removal of existing asphalt pavement and approximately 30 inches of excavation so that it will be able to move and filter run off from adjacent paved areas. The team suggested that a diverse palette of native riparian plant species be planted in the swale, including California Sycamore, wiregrass, and various sedges. The swale would be underlain with at least 12 inches of highly permeable gravel. Vertical Gardening Vertical gardening techniques can be used to grow large numbers of plants in small or narrow areas such as balconies, window sills, or along walkways. There are several ways to make vertical gardens using recycled water bottles or other plastic containers. Lattice fences, balcony dividers, or simple string and net supports are other types of vertical garden structures that can help to produce food and flowers in small spaces. This is an example of one type of gardening that could become part of an expanded neighborhood gardening program at the school. SUMMARY School sites are located throughout our region. Presently they use more than their share of water and energy, and they contribute more than their share to the problems of flooding and solid waste disposal. This can easily change. The large open areas that typically characterize these sites provide ample opportunity for on-site water re-use and stormwater bio-remediation. In fact, as the Crenshaw High School charrette team demonstrated, we can probably use school sites to improve the water quality of storm run off from surrounding streets for little or no cost. CONSTRUCTION BUDGET The charette team provided a preliminary construction budget for the proposed work, rounded in 1997 dollars, as follows: All proposed site improvements, including parking, planting, graywater irrigation system, vegetated swales, and cisterns = $1,200,000 Construction Contingencies (30%) = $360,000. TOTAL ESTIMATED COST OF CONSTRUCTION: $1,600,000. Note: Additional professional design fees for engineering and landscape architecture (allow 20% of total construction budget) = $320,000. BENEFIT ANALYSIS The following benefit analysis provides a cost value per year, per thirty years, and a total value over thirty years for remediation of the entire property. This information is provided in 1997 dollars.
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