Rainwater Harvesting:

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Rainwater Harvesting Raingardens and
Stormwater Justin Mechell Texas AgriLife
Extension Service Department of Biological and
Agricultural Engineering Texas AM University
System
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Why Harvest Rainwater?

• Accumulated rainwater volumes from common
  rainfall events (Based on a 100ft2 catchment area
  and 100 collection efficiency)

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Average Annual Precipitation (in) from 1971-2000

• From TWDB 2007 State Water Plan

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Projected Population Growth in Texas Counties

• From the TWDB 2007 State Water Plan

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Major Aquifer Water Level Drops in Texas
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Meeting the Water Demand Texas in 2050 21
million acre-ft/year
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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

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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

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Raingarden Components
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Raingarden Components

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

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Why Put in a Raingarden?

• Water is a valuable resource
• Urbanization
• Increased runoff frequency and volume
• Thermal shock
• Runoff quality
• Groundwater recharge

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Increased Surface Runoff
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Stormwater Runoff Rate
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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

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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.

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Water Quality Impairments

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

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Water Quality Impairments, Contd
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Is a raingarden feasible?

• Utilizes current guttering and downspouts
• Materials
• Shovel, rake, carpenters level, stakes, string
• Gravity-fed system
• No pumps or electricity needed

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When is a raingarden not feasible?

• Existing landscaping
• Slope
• Space

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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

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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

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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

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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

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How do I determine where the system should be
located?
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How do I determine where the system should be
located?
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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

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How do I determine the size of my raingarden?

• Slope
• Soil texture class
• Distance from downspout
• Catchment area

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How do I determine the size of my raingarden?

• Slope
• Recommended design depths for selected slopes
• Minimizes effort

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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

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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

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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

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How do I determine the size of my raingarden?

• Soil Texture Triangle

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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

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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).
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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).
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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

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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

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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

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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

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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

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Questions?

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