URWH at various scales

Transcription

1 URWH at various scales Training programme on Mainstreaming Sustainable Urban Water Management March 23-26, 2015

2 Structure of Presentation Surface runoff/ flood management practices to ensure runoff quantity and quality through public open spaces. Urban rain water harvesting at institutional/building scale- case example Birkha Bawri Potential green space for different land use areas Characteristics of required drainage system according to land use Integration of different drainage structures for Surface runoff/ flood management swale, bioretention, detention ponds and ponds Reduction in overall Runoff Coefficient and increase in retention for an urban area (Example Dwarka, Delhi) by using existing open spaces at three different scales: a) Palam drain catchment level b) Neighborhood level- sector 23 c) Potential area for regional flood water harnessing

3 Conventional Drainage Precipitation: Rainfall Rapid conveyance of water & pollutants watercourses

4 Discharge Why are efficient drainage system needed? Hydrograph: Peak discharge becomes larger Time Floods occur quicker due to reduced infiltration Attenuate flow Promote infiltration & groundwater recharge Surface /flood management practices

5 Efficient drainage systems - Surface /flood management practices Manage the flooding and pollution aspects of drainage and ensure that the community and ecology are considered in the design. These peactices deliver efficiently and effectively across four key criteria: Quantity Quality Amenity Biodiversity

6 Efficient drainage systems - Surface /flood management practices at different scales A water sensitive house A water sensitive sector A water sensitive city

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8 Birkha Bawari: Objective The Birkha Bawari is designed as a monumental rainwater harvesting structure in Umaid Heritage Township which is based on the concept of both Kunds and baoli (also referred as bawari ) which were the traditional practice of rainwater harvesting in Rajasthan and Gujarat Implementation: Birkha Bawari- RWH structure, is the part of Umaid Heritage- Housing complex and is implemented as the part of township by the same developer. The structure is designed by Architect Anu Mridul.

9 Location Location Map of Umaid Heritage in Jodhpur, Rajasthan The site is located in the city of Jodhpur where the traditional water management system is getting gradually destroyed due to modernisation and urbanisation.

10 Salient features PARAMETERS Total catchment area Green area irrigated Capacity of RWH structure (bawari the storage tank) Volume of rainwater harvested Cost of System ( in Rs) Savings per annum DETAILS OF THE RWH SYSTEM 110 Acres 15 Acres Year of RWH system implemented million liters Approx 21.1 million liters per annum 80 million 2.36 million per annum

11 Conveyance system Inlet for road side drainage Open channels; grated underground storm water drains connecting roof tops The rainwater is collected from rooftop and road channels through storm water drains; open channels and slots. The runoff from the phase-ii is collected from the storm drains and connected to the drains in phase-i sloping towards the RWH structure - Birkha Bawari, located in Phase I of the complex.

12 Design specifications Parameters Length Width Average Depth Maximum Depth Average Water Depth Wall Thickness Specification 135m 10.5 m 11m (bgl) 18 m (bgl) 7m 0.7 m

13 Benefits of the project executed 17.5 million liters of water from the Bawari is used for landscaping. The same water load is reduced from the other water supply of the region. Birkha Bawari enables a savings of up to Rs 2.36 Million annually for the residents of Umaid Heritage. Tanks: thus by using the alternate source of water about Rs Million are saved annually. + Reduced load on municipal storm water infrastructure. + Increase in value of Property + Aesthetic Value

14 Benefits of the project executed The housing, Umaid Heritage has around 20% of green area, where the stored water is used for watering the landscaped area of the housing complex. + Recreational Activities + Knowledge Dissemination The housing colony promises green areas and cleanliness with traditional water harvesting monumental structure which clears off the water from the roads and makes us the proud resident of the society - Kamla Jain, Resident The beautiful monumental Bawari is one of the feature of the housing giving the royal ambiance and serves the environment which adds to the property value of the plots and flats - Ajay Mathur, Marketing manager and resident

15 Surface /flood management practices in public open space Public open space for such practices are characterized by being located within green space or other clearly defined public areas that can manage the storage and conveyance of surface water runoff. Depending on the design and characteristics of the site there will be a convenient location where the intermediate source control area becomes part of accessible public open space.

16 Integrating different Surface /flood management practices options Porous paving eg reinforced grass or gravel surfaces, porous concrete and porous asphalt Filter strips Swales Bioretention areas and raingardens Detention basins Porous paving swale Filter strip

17 Runoff Volumedecrease How would these practices cater the quantity of storm water Increase in time of concentration Peak Discharge- Reduce Heavy Metals How would these practices handle the quality of storm water Sedimentation Filtration Land-values Recreation opportunities Wildlife habitats How can these provide Amenity value Aesthetic & Ecological quality of the landscape Educational opportunities

18 Swale Swale is densely vegetated trapezoidal or triangular channels with low pitched side slopes designed to convey runoff slowly Used to capture, direct and infiltrate rainwater into the soil Alternate to curb and gutter system

19 Swale

20 Swale example

21 Swale design-design Criteria Land Uses Residential, commercial, or institutional development conditions Residential uses -densities of 4 dwelling units per acre. Large commercial site applications - may require multiple channels according to sub catchments Location Next to roads Landscape areas Adjacent to car parks Landscape areas Highway or low- and medium-density residential road runoff, (adequate ROW) Other suitable areassports fields, golf courses, and other turf-intensive land uses

22 Swale design-design Criteria Soil Requirements It should not be constructed in gravelly and coarse sandy soils (cannot support vegetation). Thumb Rule 1: Soil infiltration rate > 0.2 mm/s (avoid compaction of the soil) Vegetation Fine, close growing, water resistant grass (more the surface area of the vegetation exposed to runoff more the effectiveness of the system). Examples: Reed canary grass, grasslegume mixtures, and red fescue.

23 Geometry Shape: Trapezoidal cross section Side Slope: 1:3 (recommended to maximize the wetted channel perimeter of the swale) Longitudnal Slope< 2% if drain tile is incorporated and Slope> 4% can be used if check dams are placed in the channel to reduce flow velocity Thumb Rule : The total surface area of the swale should be 1% of the area that drains to the swale Thumb Rule : for the effectiveness of the swale to treat runoff, depth of the storm water should not exceed the height of the grass.

24 Open channel flow, such as in a swale, is based on two formulas 1. Manning s Equation 2. Continuity Equation Flows The flow velocity is maintained at 0.5m/s (Austrailan manual) Maximum flow rate < 140 litres/second (0.14 m3 /s) (EPA manual) Continuity Equation Flow rate and velocity q = A V q flow in cu. ft/s A cross-section area for flow, sq, ft V flow velocity, ft/s

25 Manning s Equation Velocity of flow in an open channel is given by Manning s Equation V = (1.486 R 2/3 S 1/2 ) / n V flow velocity, ft/s N Manning s roughness coefficient for open channels R hydraulic radius, ft S channel slope, ft/ft Manning s n values for various channels. Type of channel Lining Design n Grass Riprap Turf Reinforcement 0.038

26 R - Hydraulic Radius R = cross-section area of flow / wet perimeter Water Surface Wet Perimeter 4 5 Area = 20 sq, ft WP = = 13 ft R = 20/13 = 1.54 ft 1 20 Area = 20 sq, ft WP = = 22 ft R = 20/22 = 0.91 ft Larger R = less resistance to flow

27 Bio retention basin It is a planted depression that allows rainwater runoff from impervious urban areas like roofs, driveways, walkways. This reduces rain runoff by allowing stormwater to soak into the ground Rain gardens can cut down on the amount of pollution reaching streams

28 Bio retention basin

29 Bio retention design-design Criteeria Land Uses Residential, commercial, institutional development Location Parking lot islands. Parking lot edge. Road medians, roundabouts Right-of-way or commercial setback. Courtyards. Individual residential lots. Unused pervious areas on a site.. Retrofitting

30 Bio retention design-design Criteria Land Uses Residential commercial institutional development Available Space. The bioretention surface area will be approximately 5% to 7% of the contributing drainage are

31 Bioretention areas

32 Components of bioretention area: Grass filter strip/ grass channel: To reduce incoming runoff velocities and to filter particulates Ponding area For temporary storage of surface water Plants To provide vegetative uptake of pollutants.

33 Bioretention example

34 Bioretention Pollutant Removal University of Maryland Box Experiments Cumulative Depth (ft) Copper Lead Zinc Phosphorus TKN Ammonia Nitrate Removal Efficiency (%) Field Dr. Allen Davis, University of Maryland

35 Infiltration System 2 Mulch 2 Existing Ground Highly Pervious Soils

36 Combination Filtration / Infiltration 2 Mulch Existing Ground 2 Sandy Organic Soil Drain Pipe Gravel Moderately Pervious Soils

37 Detention basin

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39 Detention basin example

40 Ponds

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44 Factors for designing effective Surface /flood management practices Approach for catchment development Time of Concentration- Increase Scope of development Lengthening flow paths and thus reducing the length of the runoff conventional conveyance systems. Runoff Volumedecrease Peak Discharge- Reduce Water Quality- Improve Floodingcontrolled Reduce/minimize imperviousness, preserving more trees and meadows. retention storage for volume and peak control, natural drainage patterns According to catchment landuses, sand filters, retention areas use of additional runoff, use of flood water in low lying area

45 RAINWATER: Availability in area, management to meet water demand in local areas. WASTE WATER: managed and reused for non domestic purposes References STORM WATER: managed through surface water bodies+ optimal storm water channel : Green infrastructure Urban Development: planned and executed in a manner Sheet so No. as 2 to lower the hydrological impact of urbanization and present opportunities for improved water management Storm water and resource management- case study Dwarka

46 Steps for analysing catchment areas a) Delineation of Catchment area b) Calculation of runoff discharge Preparation of suitable sustainable urban drainage system strategies c) Identifying potential sustainable strategy

47 Catchment analysis K M References Landscape architecture time saver standard by Charles w. Hanis and Nicholas Tines Table: calculation of discharge for each of catchment area of drain for 25 year peak hour rainfall. Scale: 1:300 landuses Runoff coefficient (80% Impervious) Commercial 0.7 (70% impervious) public-semi public 0.6 Park 0.3 Trunk drains TD Cusec TD Cusec Discharge Capacity Area Cumecs (%) Increase in discharge Storm water and resource management- case study Dwarka Delineation Sheet No. 6 of Dwarka into different catchments of respective trunk Watershed analysis drains

48 Institutional Conventional break up of open areas for Dwarka, sector 23, Delhi DDA Housing 33% 33% 34% 36% 20% 14% 5% 25% Group Housing 22% Built up % 46% 29% 3% Open vegetative % Open paved% Open lawn area % The conventional practice of making the surface paved, leads to loss of opportunity space for rain water harvesting structure and also increase the runoff coefficient. However, the existing lawn/green space can be used to their full potential for designing and planning of rainwater harvesting structure.

49 Palam drain catchment level 4 2 Application of Sustainable strategy for Palam drain watershed area of Dwarka R 1 Swales Public open space-district park Area- 8% of public open space of watershed area Filter Strip: Volume- 20% of annual rainfall falling in the watershed (113095mm) Thus 5% to 15% area of open space of each catchment area can retain 100% of 1 hour Peak Discharge from watershed for 25 year storm. Along road R 1 Strategies for watershed area with case example of one of the watershed of drain TD-3 (Palam drain) RWHs in Catchment area for drain TD-3 Area (sqm) Depth (m) volume (Cum) Bioretention pond pond swale Retention basin retention basin gully trenches total area total Storm water and resource management- case study Dwarka References Suds Manual. London: NRCS Planning and Design manual. Storm Water Management for Industrial Activities. Simpson, P. (2010). Towards sustainable water stewardship. Greater Dublin Strategic Drainage Study. Application of strategy for one of the Catchment area

50 Potential area for regional flood water harnessing For using the total potential of low lying area of site: By Construction of No. Of ponds to increase the capacity (depth not more than 0.6 m). Construction of inflow and outflow gates with sluice water movement and collection The total water collection by direct precipitation and by no. Of ponds is 6 mcm. This 6 mcm of water shall be used for bulk uses of Dwarka. Outlet gate Direct precipitation over depression: 1.4 Mcm (6437 mm x 150 Ha x.3 coef) Regional flood: 37 Mcm Evaporation loss = 30% = 1mcm Total water storage capacity : 6Mcm Inlet gate Use of water: Horticulture Construction works Overall Runoff coefficient reduction from 0.62 to 0.4 Major conclusions (Specific to Dwarka): Potential area in site for flood water harnessing Typical section through natural reservoir If strategies for only reduction of overall runoff coefficient are applied than 22% of reduction in peak discharge achieved. And after that if retention strategies for effective drainage systems applied for 5-10 % of public open space than 100% of exceeding peak discharge is reduced. Storm water and resource management- case study Dwarka