Rainwater Harvesting and Stormwater Drainage Assignment
Ring main for micro-sprayer irrigation system
Legend:
Area surrounding the recreation centre comprises a mixture of gravel paths, garden beds, trees and porous paving. TP = DN25 water service tapping point, C = Café with outside seating, O = Building manager's office, TB = toilet block. Preamble: The Client proposes to develop a Sports and Recreation Centre and accompanying paved car park on a site that was originally a municipal council depot. The main objectives are (i) to make substantial savings in potable water consumption by harvesting rainwater for toilet flushing and landscape irrigation, and (ii) to have tank water available for at least 80% of the time in dry years and at least 90% of the time in years with typical rainfall.
Tasks:
1. Design a system of flat eaves gutters, downpipes, and rainwater tanks to collect roof runoff from the proposed community sports and recreation centre based on an ARI of 20 years. Adopt a dry pipe system with DN150 PVC downpipes and a time of concentration to each raintank of 5 minutes. Site location is at 37.67S latitude and 145.16E longitude, the metal-tray roof dimensions are 72 x 37.25 and the natural surface level is relatively flat with an RL of 60.00 m AHD.
2. Tank water is to supply the following end uses: (a) Landscape watering from an irrigation system (allow 3 kL/d during October to March) comprising seven zones, each fed from branch points on a ring main. Required flow and pressure at each branch point is 25 L/min and 30m, (b) 12 dual-flush toilets and four urinals (allow 1350 L/d throughout the year). Potable water will supply all hand basins and all café taps and appliances (allow 900 L/d throughout the year). Provision is to be made for an automatic potable back up supply when the raintanks are empty via 40m of DN25 Type B Cu property service pipe and dual-supply diversion valve. The available residual head at the TP varies from 450 to 500 kPa. Determine suitable sizes for the ring main and the service pipe to the toilet block to match the suggested pump and filter.
3. Overflows from the tanks are to be piped to the existing DN450 RC drain (design ARI = 10 years) with provision made for on-site detention within the raintanks. The recreation centre site was originally used for vehicle storage and had a fraction impervious of 0.30 and a Tc of 5 minutes and only the impervious areas were directly connected to the drain.
4. Design a piped stormwater drainage system (minimum DN225) for the car park (surface slope 1 in 200) with outflows to pass through a separate on-site detention facility. Grade pipes to run ‘just full' where possible and include a sketch of the OSD facility. The car park area previously consisted of storage sheds and roadways and had a fraction impervious of 0.60 and a Tc of 5 minutes, and only the impervious areas were directly connected to the drain. Existing DN450 RC stormwater drain (1.2m cover) (South elevation of building) N C O TB Scale 1 in 1000 Up to 300 persons per day between 9am and 9pm Creek.
5. Your report, prepared to professional standard and arranged in a logical order, is to include (a) detailed design calculations clearly set out with all assumptions made clear, (b) schematic diagrams (drawn to scale) showing the final arrangement for the roof drainage system, raintanks, pump & filter, all associated pipework and equipment, and all stormwater drainage works, (c) details (including discussion) of the rainwater pump & filter selected, the sizing of the ring main and the toilet block service pipe and diagrams of both HGLs, (d) total annual water use, graphs showing rainwater yield and potable water savings versus raintank capacity, and an estimate of annual potable water cost savings.