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Aquascape facilities have traditionally been considered ornamental, and landscape features have primarily served aesthetic purposes in golf courses, parks and residential developments. However, aquascapes can be applied with innovative design elements to function as primary stormwater infrastructure in urban developments, replacing typical stormwater facilities and adding value to communities. These specialized types of aquascape systems integrate a living ecosystem into an urban environment, which maintains water quality through natural biological processes. Planned aquascape features, particularly in semi-arid areas, offer many unique advantages for stormwater management that are not available in conventional engineered systems, including: (1) continuous year-round natural treatment process; (2) stormwater conveyance and storage; (3) enhanced rates of water quality treatment; (4) flood protection; (5) combined land use elements; (6) significantly reduced infrastructure costs; (7) dry weather flow treatment; (8) landscape and aesthetic treatment with natural water system; (9) increased surrounding land values; (10) natural ecosystem benefits; (11) recreational design feature; and (11) urban design element for communities. The necessity for stormwater pollution control has received increased public attention, especially with the escalating environmental regulations focusing on nonpoint source pollution and protection of receiving waters. As of March 2003, the Phase 2 portion of the NPDES (National Pollutant Discharge Elimination System) stormwater regulations require developers and municipalities to more seriously address stormwater quality through the implementation of standard structural control measures or best management practices (BMPs). Standard structural control methods generally have limited pollutant removal effectiveness; perform single functions; require considerable land; have numerous maintenance issues/construction costs; have difficulty integrating with the land plan; and are typically unsightly having limited aesthetic appeal to a community. Integrating large scale specialty aquascape systems through constructed lakes, ponds, small creeks, or other water features can replace traditional underground drainage infrastructure and provide highly effective stormwater treatment, resulting in water quality not available through other conventional methods. INTEGRATING STORMWATER TREATMENT Providing the stormwater treatment function as part of an aquascape relies on recreating a natural ecosystem that can utilize biologic processes for treatment of urban pollutants in runoff, and on maintaining the normal health of the aquascape system. The primary elements that have been integrated into this unique type of treatment aquascape system include: (1) wetland planters; (2) biofilter beds; (3) pretreatment wetland filters; (4) aeration; and (5) stormwater retention volume/capacity. When successfully applied, these features have been shown to achieve exceptional water quality results. Pretreatment of stormwater is critical to enhancing the overall performance and should be performed for all inflows into the aquascape in order to trap larger sediments. Wetland filters or vegetated "first flush" basins can serve as pretreatment devices; they should be installed at the outfall of all storm drains prior to entering the aquascape. Biofilters consist of separate self-contained submerged gravel beds adjacent to the perimeter of the aquascape through which water is circulated and distributed via a slotted pipe system. A naturally occurring biological mass (microorganisms) will coat the gravel and serve to strip the water passing through the filter of nutrients (nitrogen, phosphorous) that would otherwise promote algae growth. In addition, the recirculation pumping reintroduces oxygen into the aquascape system and increases the overall aquascape dissolved oxygen content. The combination of limited food supply and aerobic conditions reduce the potential for eutrophication. A critical feature necessary to incorporate into the biofilter design to ensure long-term performance is the ability to effectively perform periodic backwashing to remove material that accumulates within filter voids and prevents adequate filtration. A separately engineered backwash system should be implemented, as simply reversing the direction of flow through the biofilter piping system is not sufficient to distribute flow. A simple backwash system to employ involves a portable pump that is lowered into a screened standpipe within the biofilter; then the water is drawn through the biofilter in a reversed direction to the screened standpipe, discharging to the sanitary sewer. It is recommended that maintenance personnel use rodding or mechanical means to break up the gravel bed "packing." Another important design aspect of the biofilters is the layout and location of these features to promote the maximum water quality benefit. A stabilized biological aquascape system requires maintenance of the dissolved oxygen levels to eliminate the potential for odor problems and other aquascape operating issues. Maintaining necessary dissolved oxygen levels can be achieved through the application of a fine bubble diffusion system (aeration) placed along the bottom of the constructed aquascape. Additional benefits of aeration include destratification of the aquascape's water column to reduce surface water temperature and enhancing the natural vertical movement or circulation patterns. The aeration utilizes low-pressure air compressors/blowers -- sized to provide necessary currents that promote transport of water from multiple liquid layers. The ability to develop extremely fine bubbles can be achieved through the use of aeration disk pods manufactured with a flexible rubber skin that precisely control the size of the bubbles. The importance of the fine bubbles, compared to the large bubbles from a simple perforated pipe system, involves the increased contact area provided by the fine bubbles enhancing oxygen transfer. Separate wetland planters located along the perimeter of the aquascape's edge will also assist in promoting the overall water quality objective for the aquascape system. The wetland planters can be constructed along shelves in the lake shoreline with submerged walls separating the plants from the lake (except for the crest) to allow for submergence from the water level. The wetlands function to filter out waste from the lake water through various natural chemical and biological processes. SUCCESSFUL AQUASCAPE TREATMENT APPLICATIONS A new 70-acre planned residential community known as Bridgeport was developed in the city of Valencia, located in northern Los Angeles County, California. It incorporates a manmade lake system for stormwater management and treatment. A residential development plan had been originally adopted that utilized a conventional storm drain system, but did not provide for stormwater treatment. This site plan was modified during the initial planning to eliminate all underground storm drain pipe infrastructure within the project by integrating a manmade lake system that extended throughout the interior of the entire development project. The lake system has three primary functions: 1) an aesthetic focal landscape feature for the project, 2) serves as the primary drainage conveyance within the development, and 3) the lake provides runoff water quality treatment from the development. The developer realized additional benefits from the constructed lake system through the cost savings of the eliminated storm drain pipe and the added value to the project that translated to increased residential lot premiums for lake views. Runoff from the 70-acre residential area was a tributary to the 15 acre lake, which has an operating water volume of approximately 105 acre-feet, an average depth of approximately seven feet, and a maximum depth of 12 feet. The lake is lined with 30-mil PVC and equipped with a leak detection system located below the liner. The water quality treatment features incorporated into the lake system include: aeration, lake biofilters, wetland planters, and vegetated pretreatment basins. These features function to manage the urban storm runoff quality and the health of the lake system to ensure that any discharges to the adjacent Santa Clara River have an improved quality. The Bridgeport Lake system incorporated 15 biofilters placed at the end of each lake finger to promote the overall circulation of the lake system. Each biofilter is approximately 1,000 square feet in area and treats lake water at 500 gallons per minute (gpm), providing a total biofilter flow rate for the lake of 7,500 gpm. The biofilters are typically 3 to 4 feet deep, filled with gravel and submerged 18 to 24 inches below the lake surface. Water pumped from the lake is distributed through the biofilter via a herringbone-slotted pipe system underneath the gravel bed. Recirculation takes place 24-hours a day through the biofilters; the time needed for complete filtration of the lake is approximately three days. The Bridgeport Lake system has a higher than industry average turnover rate and incorporates biofilters provide a significantly higher level of water quality and aids in stabilization of the lake water quality. Aeration for the Bridgeport Lake is provided via a fine bubble diffusion system incorporated into the bottom of the lake. This system utilizes 12 five cubic feet per minute (cfm) compressors that deliver 60 cfm to 30 aeration disks in six groupings around the lake. The aeration system is sized to turn over the lake water every three to four hours if the aeration is operating 24-hours per day. The Bridgeport Lake water quality was also enhanced through the pretreatment of all stormwater runoff entering the lake via submerged wetland planters along the perimeter, analogous with the function kidneys. Approximately 18 water quality filters, with an average surface area of 250 square feet, intercept runoff prior to discharging into the lake, the filters are located at all the inflow points. The typical configuration consists of the storm drain pipe discharging into a vertical stand pipe, such that the bottom end allows nuisance flows to discharge into the gravel bed underneath the entire water quality filter. High flows would overtop the planter weir into the aquascape. The planters are located intermittently along the lake edge based upon project aesthetics and overall lake water quality operation. The constructed Bridgeport Lake system has been operating since 1999, and there is an active water quality monitoring program to evaluate the overall health and operation of the lake. The unique trends observed from the data indicate that (1) the make-up water required to offset evaporation is only 70% of the anticipated amount because of nuisance water reuse, and (2) application of algaecides are 50% less than normally required for a lake of this size. This is just one example of the successful application of constructed aquascape systems to provide stormwater treatment. The results demonstrate that exceptional water quality can be achieved far beyond the traditional methods being employed, while providing many additional benefits to the surrounding community.

Project Contributors: Lake System Design: Pacific Advanced Civil Engineering, Inc. Developer: Newhall Land Landscape Architect: The Collaborative West Civil Engineer: Alliance Land Planning and Engineering

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December 10, 2019, 7:01 pm PDT

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