Dotty Woodson Extension Program Specialist- Water Resources Texas AgriLife Extension

Transcription

1 Rainwater Harvesting Dotty Woodson Extension Program Specialist- Water Resources Texas AgriLife Extension

2 Solomon s Pools

3 Sigiriya, Sri Lanka

4 Pont du Gard 9 Century

5 Four Rivers

6 Byzantine Water Cistern 6 th Century

7 Rainwater Harvesting Water Resources Well water Municipal water Rural Water Provider Rainwater Harvesting

8 Why Collect Rainwater P.6 gallons per square foot roof per 1 rainfall P 2,000 sq. foot roof X 1" rain = 1,200 gal. water P 1,200 gal. X 32" rainfall per year= 38,400 gal/yr

9 Rule of Thumb: 1 square inch of downspout per 100 square feet of roof top 2 inch by 3 inch downspout = 600 square feet of roof top 600 X = 374 gallons 3 inch by 4 inch downspout = 3 inch by 4 inch downspout = 1,200 square feet of roof top 1,200 X = 720

10 What is Rainwater Harvesting? Rainwater Harvesting is the capture, diversion, storage and distribution of rainwater for later use Why Rainwater Harvesting Saves money Reduces demand on municipal water supply Makes efficient use of a valuable resource Reduces flooding, erosion, and contamination of surface water Tarrant County Community Garden

11 Development Impacts on the Water Cycle 40% 30% 10% 50% 55% 15%

12 Development Impacts on Water Quality Increased Quantity Decreased Quality Fertilizer Pesticides Pathogens Sediment Toxic Contaminants Debris Thermal Stress Greater Speed

13 Urban Water Budget Pavement and Rooftop Scenario ROOFTOP RUNOFF!! EVAPORATED WATER INFILTRATION?? SURFACE RUNOFF!! GROUNDWATER??

14 Urban Water Budget Rainwater Harvesting Scenario ROOFTOP RUNOFF!! Cistern Rain Garden

15 Stormwater goes untreated into the nearest creek

16 Where to Rainwater Harvest? Large or Small Landscapes: Homes Parks Schools Commercial Sites Parking Lots Apartment Complexes Cabins Barns Greenhouses

17 How Rainwater ate Harvesting Works A rainwater harvesting system consists of The supply rainwater The demand landscape water requirements Collection system gutters and downspouts Storage - tank Delivery system drip irrigation Simple and complex systems Simple distribute rainwater immediately Complex store some or all of rainwater for later use

18 Supply: Rainfall Supply comes from runoff,, rainwater that flows off a surface If the surface is impermeable, runoff occurs immediately: Pavement Concrete Roofs If the surface is permeable If the surface is permeable, runoff occurs after the soil is saturated

19 Demand: Plant Water Requirements The amount of water required is determined by Plant Water Requirements Evapotranspiration Irrigated area square feet Number of Plants Growth stage of Plants Time of Year Native and Adapted d Plants Require Less Water Austin, TX

20 Simple Rainwater Harvesting Systems Rain Garden Catchment Distribution System Landscape Holding Area Catchment Any hard surface where water runs off (e.g. roofs, pavement, or soil surface) Amount depends on Catchment Size, Surface Texture, Slope and Rainfall

21 Simple Rainwater Harvesting Systems Distribution System Channel water from catchment to landscape holding area Include gutters and downspouts, sloped sidewalks, hillsides, street curb cutouts, channels and ditches Use gravity, gates, or a small pump to cause flow through the distribution system Simple System at School

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25 Complex Rainwater Harvesting System Complex systems Water storage Cost more to build Yields greater water savings Factors to consider Availability of other water supplies for irrigation Need for professional assistance in design and construction Cost of storage container, pumps, and maintenance Long investment payback period several years Personal commitment to water conservation ethic

26 RWH Expenses Collection System Barrel/Cistern Delivery System Irrigation or Shallow Well pump Pressure Tank Backflow Preventer with double check valve and air gap (RPZ)

27 RWH Expenses Rain Barrel < $0.50/gallon Poly Tank < $1.00/gallon Fiberglass Tank < $2.00/gallon Swimming Pool Under Deck Underground Professional Design and Installation $4.00 or >

28 Complex Rainwater Harvesting System Storage Costs depends d on: Type of catchment and conveyance system Degree of filtration Distance between container and area irrigated Containers

29 Complex Rainwater Harvesting System Catchments Yield depends on size and surface texture Surface textures include: High yield concrete, asphalt, and smooth roofing material Medium yield bare soil; compacted clay best Low yield areas with plants, such as grass or groundcover

30 Complex Rainwater Harvesting System Collection Systems Direct water from catchments to storage containers Roof collection systems use gutters and downspouts to direct water into storage containers

31 Complex Rainwater Harvesting System Storage Storage makes rainwater available when required Filtration filter before storage Filtration considerations include: Degree of filtration depends on size of distribution tubing and emission devices used Type of filter inline, leaf/insect screens, roofwasher, first flash diverter

32 Complex Rainwater Harvesting System Storage Containers may be made of polyethylene, fiberglass, wood, concrete, or metal underground or aboveground

33 Rainwater Harvesting System Storage

34 Rainwater Harvesting System Storage

35 One Leads to Another

36 Garden Faucet Attachment

37 Underground Storage

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39 Large Above Ground Cistern

40 Large TAMU

41 Complex Rainwater Harvesting System Storage container placement Elevate above-ground containers to take advantage of gravity flow Put storage containers near plants and near end of downspout Use several small cisterns because easy to handle and camouflage Connect several tanks for large landscaped areas

42 Metal Tanks

43 Rainwater Harvesting System Storage

44 Rainwater Harvesting System Solar Power for Irrigation Pump

45 Air Conditioner Condensation Harvesting System Storage

46 How much water comes from A/C Condensate per day Window A/C unit can emit 1-2 gal of condensation Homes = 3-10 gal per 1,000 sq ft of airconditioned space Note: A 10,000 sq ft office building can produce more than 15,000 gal per year Source: org/condensate aspx

47 Rainwater Harvesting System Storage

48 Rainwater Harvesting System Storage

49 Rainwater Harvesting System Filter

50 Rainwater Harvesting System Filter

51 Complex Rainwater Harvesting System Storage

52 Filters for Rain Barrels

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54 Rainwater Harvesting System Filter Rainwater Harvesting System Filter First Flush Diverter

55 Rain Aid

56 Potable Water Filtration

57 Bushman Wall Cistern

58 Portable

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64 Wildlife Cistern

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67 Rainwater Harvesting System Distribution System Distributes water to plants from storage containers Use garden hoses, soaker hose, or drip system Use pump either electric or solar powered If the system is integrated with municipal supply, install a backflow preventer double check valve with an air gap or other approved backflow device

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70 Design and Build a Complex Rainwater Harvesting System Step 1: Site Analysis Draw the site to scale, using arrows to plot existing drainage patterns, and show high and low areas. Identify possible catchments, such as pavements, roof surfaces, and bare earth. Identify areas requiring i irrigation i and sites close by for storage (above ground or underground). Plan ways to move water from catchments c to storage containers or holding areas, using gravity when possible. Plan ways to move water between landscaped areas.

71 Design and Build a Complex Rainwater Harvesting System Step 2: Calculate Supply SUPPLY (gal) = Rainfall (in) x x Catchment Area (sq ft) x Runoff Coefficient Multiply rainfall in inches by to convert inches to gallons per square foot. Multiply the result by the area of the catchment in square feet. Multiply this result by the runoff coefficient to obtain the available supply. The runoff coefficient is the percentage of total rainfall that can be harvested from a particular source.

72 Example 1: Calculating Supply Calculates the catchment area. The eave-to-eave measurements for section A are 45 x 25 section B are 20 x 25 : 1,625 sq ft of catchment area. Rainfall (in) x x Catchment Area (sq ft) x Runoff Coefficient = SUPPLY (gal)

73 TAMU Rainwater Harvesting Calculator l GO TO

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76 Example 1: Calculating Supply Average Monthly Rainfall (Inches) for Texas Cities* Cities Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Austin Dallas/FW El Paso Houston Runoff Coefficients** i Character of Surface High Low Roof Metal, gravel, asphalt shingle *Office of the State Climatologist Paving < Concrete, asphalt **Haan, C.T. et al. Design Hydrology and Brick Sedimentology for Small Catchments, 1994.

77 Example 1: Calculating Supply Rainfall Harvesting Supply Worksheet A B C D E F Multiply D by Follow the Enter the Multiply A by Enter the Multiply B by E to obtain Enter the runoff lettered rainfall to convert square footage C to yield the the total coefficient for instructions amount in inches to of the gross gallons of monthly yield of your catchment for each inches for gallons per catchment rainfall per harvested surface. month. each month. square foot. surface. month. water in gallons. January February March April May June July August September October November December Annual ,327 29,995

78 Complex Rainwater Harvesting System Step 3: Calculate Demand Demand ET (in) x Plant Coefficient x x Irrigated Area (sq ft) = DEMAND (gal) Determine the monthly reference evapotranspiration (ET) in inches for your area. Multiply ET by the Plant Water Use Coefficient, representing the percentage of reference ET a particular plant needs. Multiply the result by to convert inches to gallons per square foot. Multiply this result by the size of the irrigated area in square feet Find the monthly reference evapotranspiration (ET) in inches for your area at Texaset.tamu.edu

79 Evapotranspiration (ET) Evapotranspiration is the combined loss of water from the soil and wet surfaces due to evaporation and plants due to transpiration ET is an estimate of potential planted-area water demand in inches

80 Example 2: Calculating Demand Average Monthly Evapotranspiration (Inches) for Texas Cities* Cities Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Austin Dallas/FW El Paso Houston San Antonio Plant Water Use Coefficients Plant Type Coefficient Low-Water-Use (Blue Grama, Desert Willow) 0.20 Medium-Water-Use (Buffalograss, Bermudagrass) High-Water-Use (St. Augustine, Fescue) 0.75 *Office of the State Climatologist < tamu edu>

81 Example 2: Calculating Demand Follow the lettered instructions for each month. Rainfall Harvesting Demand Worksheet A B C D E F Enter the ET amount in inches for each month. Enter the appropriate plant water use coefficient. Multiply A by B to obtain plant water needs in inches. Multiply C by to convert inches to gallons per square foot. Enter the total square footage of landscaping. Multiply E by D to obtain total landscaping water demand in gallons. January February March April May June July August September October November December Annual ,201

82 Designing and Building a Complex Rainwater Harvesting System Step 4: Calculate Maximum Storage/Supplemental Water Requirements Use checkbook method to balance harvested supply and demand per month. Determine cumulative storage by adding the previous month s cumulative storage to the current month s balance. Determine storage container requirements by noting the highest h cumulative storage value. When the cumulative storage goes to zero, supplemental water will be needed.

83 Examples 1 and 2 Supply/ Demand Balance Worksheet Storage/Supplemental Municipal Use Worksheet Month Yield Demand Cumulative Storage (Yield Demand) Supplemental Use YEAR 1 January 1,512 1, February 1,594 1, March 1,722 2, April 2,369 2, May 4,301 4, June 3,918 4, July 1,850 4, ,613 August 2,342 4, ,160 September 2,733 3, October 3,517 2, November 2,351 1,761 1,332 0 December 1,786 1,206 1,912 0

84 Example 3: Calculating Demand Follow the lettered instructions for each month. Rainfall Harvesting Demand Worksheet A B C D E F Enter the ET amount in inches for each month. Enter the appropriate plant water use coefficient. Multiply A by B to obtain plant water needs in inches. Multiply C by to convert inches to gallons per square foot. Enter the total square footage of landscaping. Multiply E by D to obtain total landscaping water demand in gallons. January February March April May June July August September October November December o Annual

85 Maintenance Keep Gutter and Downspouts Clean Keep Insect Netting Intact Clean Off Insect Netting Clean Out Rain Barrel

86 Incentives Tax Exempt Reduce water bill

87 Web Site Information tamu edu

88 Resources d / tamu

89 For More Information Dr. Dotty Woodson Extension Program Specialist- Water Resources Texas AgriLife Extension Coit Road Dallas, Texas