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Rainwater Harvesting:

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Accumulated rainwater volumes from common rainfall ... Fragrances. Bloom time. Color. Tolerance of occasional standing water. Construction and Maintenance ... – PowerPoint PPT presentation

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Title: Rainwater Harvesting:


1
Rainwater Harvesting Raingardens and
Stormwater Justin Mechell Texas AgriLife
Extension Service Department of Biological and
Agricultural Engineering Texas AM University
System
2
Why Harvest Rainwater?
  • Accumulated rainwater volumes from common
    rainfall events (Based on a 100ft2 catchment area
    and 100 collection efficiency)

3
Average Annual Precipitation (in) from 1971-2000
  • From TWDB 2007 State Water Plan

4
Projected Population Growth in Texas Counties
  • From the TWDB 2007 State Water Plan

5
Major Aquifer Water Level Drops in Texas
6
Meeting the Water Demand Texas in 2050 21
million acre-ft/year
7
Rainwater Harvesting Potential
  • Residential roof area in Texas
  • 21.2 billion sq. ft.
  • Assume 5 RWH installation
  • 57,400 ac/ft/yr
  • Equivalent to 51.2 MGD.
  • Note these estimates were developed by
  • HB 2430 Rainwater Harvesting Committee

8
How Rainwater Harvesting Works
  • Types of Systems
  • Simple and complex systems
  • Simple distributes rainwater immediately
  • Complex Stores some or all of rainwater for
    later use

9
Raingarden Components
10
Raingarden Components
  • Menard City Library
  • Menard County
  • Capacity N/A
  • Catchment area 1350 ft2
  • Demand
  • Infiltration and vegetation

11
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12
Why Put in a Raingarden?
  • Water is a valuable resource
  • Urbanization
  • Increased runoff frequency and volume
  • Thermal shock
  • Runoff quality
  • Groundwater recharge

13
Increased Surface Runoff
14
Stormwater Runoff Rate
15
Increased Surface Runoff
  • Large volumes of water enter the stream more
    quickly and at higher velocities
  • Causes erosion of the streams bank
  • Occurs as part of a streams natural efforts to
    regain stability by absorbing the energy of
    flowing water

16
Water Quality Impairments
  • Stormwater carries suspended sediment that can
    cloud water, limiting the amount of light that
    penetrates the waters surface and making it
    difficult or impossible for aquatic plants to
    grow.

17
Water Quality Impairments
  • Potential to introduce new pollutants into
    surface water
  • Construction activities
  • Pesticides
  • Fertilizers
  • Spills/leaks
  • Affects human health

18
Water Quality Impairments, Contd
19
Is a raingarden feasible?
  • Utilizes current guttering and downspouts
  • Materials
  • Shovel, rake, carpenters level, stakes, string
  • Gravity-fed system
  • No pumps or electricity needed

20
When is a raingarden not feasible?
  • Existing landscaping
  • Slope
  • Space

21
How do I determine where the system should be
located?
  • Proximity to foundations
  • Location relative to downspouts
  • Ground cover
  • Slope
  • Views from the house and road
  • Existing landscape

22
How do I determine where the system should be
located?
  • Proximity to foundations
  • gt 10 feet from a structure or foundation
  • Location relative to downspouts
  • Garden will catch water from roof as well as all
    grass uphill

23
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24
How do I determine where the system should be
located?
  • Ground Cover
  • Site should have partial to full sun (not
    directly under a tree)
  • At least 4 feet of vegetation should precede the
    raingarden to provide for pretreatement

25
How do I determine where the system should be
located?
  • Slope
  • Slopes of 0-12 are most practical
  • Slopes gt 12 result in a deep raingarden and a
    lot of soil prep work

26
How do I determine where the system should be
located?
27
How do I determine where the system should be
located?
28
How do I determine where the system should be
located?
  • Views from the house and road
  • Remember to take into consideration mature plant
    height
  • Existing landscape
  • Try to incorporate and use existing features
  • Less time, work, and money

29
How do I determine the size of my raingarden?
  • Slope
  • Soil texture class
  • Distance from downspout
  • Catchment area

30
How do I determine the size of my raingarden?
  • Slope
  • Recommended design depths for selected slopes
  • Minimizes effort

31
How do I determine the size of my raingarden?
  • Water movement and soil characteristics
  • Soil characteristics influence water movement
  • Soil texture class
  • Percent distribution of different sized organic
    particles

32
How do I determine the size of my raingarden?
  • Water movement and soil characteristics
  • Soil characteristics influence water movement
  • Soil profile (horizons)
  • Impermeable layers
  • Seasonal groundwater indicators

33
How do I determine the size of my raingarden?
  • How can I determine my soil texture
    classification?
  • Natural Resource Conservation Service Soil Survey
    Reports
  • Onsite Texture Analysis
  • Texture by feel method

34
How do I determine the size of my raingarden?
  • Soil Texture Triangle

35
How do I determine the size of my raingarden?
  • Catchment area
  • Determine catchment area
  • Footprint of roof and any area of lawn between
    the downspout and the raingarden

36
How do I determine the size of my raingarden?
  • Sizing factor
  • Sizing factor for raingardens less than 30ft from
    a downspout

Sizing factors for Raingardens less than 30 feet
from a downspout (Bannerman et al., 2003).
37
How do I determine the size of my raingarden?
  • Sizing Factor
  • Sizing factor for rain gardens more than 30 feet
    from a downspout

Sizing factors for Raingardens less than 30 feet
from a downspout (Bannerman et al., 2003).
38
How do I determine the size of my raingarden?
  • Multiply the size factor from the previous tables
    by the catchment area based on soil type and
    desired depth
  • This number is the recommended raingarden surface
    area
  • If the area is greater than 300ft2 then it may be
    best to divide into multiple gardens

39
How do I determine the size of my raingarden?
  • Typically raingardens are designed in a 2 to 1
    length to width ratio
  • Sizes, shapes, and orientations vary based on
    site
  • High spots in the garden will cause water to pond
    and not allow even infiltration

40
Construction and Maintenance
  • Key to the success and long-term operation of the
    system
  • Soil Compaction
  • Compacted soil has a low infiltration rate
  • Aeration or loosening of the soil may be needed
  • Berm
  • Utilize as much of the soil from the garden
  • Compact soil on the berm
  • Gentle slopes

41
Construction and Maintenance
  • Vegetation
  • Berm
  • Nursery propagated plants (1-2 yrs old)
  • Plant characteristics
  • Plant height
  • Fragrances
  • Bloom time
  • Color
  • Tolerance of occasional standing water

42
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43
Construction and Maintenance
  • Weeding
  • Mandatory maintenance
  • First two years are critical
  • Spring Chores
  • Cut back growth to 6-8 inches
  • Can be left in the garden or removed depending on
    organic needs
  • Aerate and loosen the soil to a depth of 3-5
    inches

44
Questions?
  • Presentation is based on
  • Rainwater Harvesting Raingardens
  • TCE Booklet L-5482
  • Web Address
  • rainwaterharvesting.tamu.edu
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