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A primary purpose of many dams, both large and small, is to facilitate water diversions. Although existing water supplies can be stretched much further and new water infrastructure can be delayed using water conservation and efficiency strategies described below, people will continue to divert water from rivers and other surface sources for various purposes.
 
A primary purpose of many dams, both large and small, is to facilitate water diversions. Although existing water supplies can be stretched much further and new water infrastructure can be delayed using water conservation and efficiency strategies described below, people will continue to divert water from rivers and other surface sources for various purposes.
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Nearly 80 percent of water consumed in the United States comes from surface supplies—rivers, creeks and lakes. [1] In California alone, there are more than 25,000 points of diversion from streams.[2] Thus, there are at least 25,000 locations in the state at which fish and other river organisms can be harmed in the process of meeting our need for water. In many dam investigations, the question comes down to: could we still divert water if the dam is removed or modified, or not built at all? In many cases, the answer is yes. Several, more river-friendly alternatives to traditional permanent dam diversion methods are discussed below, including:
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Nearly 80 percent of water consumed in the United States comes from surface supplies—rivers, creeks and lakes. <ref>U.S. Geological Survey. Water use in the United States in 1995. Washington, D.C.: GPO, 1998.</ref> In California alone, there are more than 25,000 points of diversion from streams.<ref>Scott McFarland, California State Water Resources Control Board, personal communication, 15 November 2001.</ref> Thus, there are at least 25,000 locations in the state at which fish and other river organisms can be harmed in the process of meeting our need for water. In many dam investigations, the question comes down to: could we still divert water if the dam is removed or modified, or not built at all? In many cases, the answer is yes. Several, more river-friendly alternatives to traditional permanent dam diversion methods are discussed below, including:
 
*Infiltration galleries and wells
 
*Infiltration galleries and wells
 
*Screened pipe intakes
 
*Screened pipe intakes
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==Infiltration Galleries and Wells==
 
==Infiltration Galleries and Wells==
As an alternative to a typical irrigation or smaller water supply dam, two general types of infiltration galleries have been employed to divert water from streams: vertical wells and horizontal infiltration galleries, also known as “Ranney wells.”[3] Both types typically require pumps to draw water from the stream’s gravel substrate through perforated pipes, but in certain sites infiltration galleries can function by gravity alone.[4]
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As an alternative to a typical irrigation or smaller water supply dam, two general types of infiltration galleries have been employed to divert water from streams: vertical wells and horizontal infiltration galleries, also known as "Ranney wells."<ref>Alternatives to Push-Up Dams. Produced by the Bureau of Reclamation, Pacific Northwest Region. 10 min. 1999. Videocassette.</ref> Both types typically require pumps to draw water from the stream’s gravel substrate through perforated pipes, but in certain sites infiltration galleries can function by gravity alone.<ref>Glenn Ginter, Illinois Valley Soil and Water Conservation District, personal communication, 9 October 2001.</ref>
    
===Vertical wells===
 
===Vertical wells===
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===Infiltration Galleries===
 
===Infiltration Galleries===
Typical construction of an infiltration gallery involves placing perforated pipes in the streambed and connecting them to a collection area, or “sump” (see photo). Water seeps into the perforated pipes and flows to the sump where it is pumped out (or flows by gravity) for immediate use or storage. The size, length and depth to place the perforated pipes depends on a number of factors, including the size of the stream, rate of diversion needed, the nature of the gravel at the site and the depth to which bed scouring will occur during high flows. The perforated pipes are usually placed at least four feet deep within a bed of clean gravel at least 1.5 feet thick on all sides. The gravel, in addition to a fabric filter placed on top of the gravel layer, prevents the perforations from becoming clogged with sediment. If sedimentation is a problem, these wells can be designed with a reverse flushing feature. Depending on the site conditions and streamflow, infiltration galleries require approximately one square foot of perforated pipe surface for each gallon per minute of pumping.[5] Since 1996, the Natural Resource Conservation Service in Oregon has installed 22 infiltration galleries, some of which divert as much as 1400 gallons per minute (2.5 cubic feet per second).[6]
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Typical construction of an infiltration gallery involves placing perforated pipes in the streambed and connecting them to a collection area, or “sump” (see photo). Water seeps into the perforated pipes and flows to the sump where it is pumped out (or flows by gravity) for immediate use or storage. The size, length and depth to place the perforated pipes depends on a number of factors, including the size of the stream, rate of diversion needed, the nature of the gravel at the site and the depth to which bed scouring will occur during high flows. The perforated pipes are usually placed at least four feet deep within a bed of clean gravel at least 1.5 feet thick on all sides. The gravel, in addition to a fabric filter placed on top of the gravel layer, prevents the perforations from becoming clogged with sediment. If sedimentation is a problem, these wells can be designed with a reverse flushing feature. Depending on the site conditions and streamflow, infiltration galleries require approximately one square foot of perforated pipe surface for each gallon per minute of pumping.<ref>Department of Agriculture, Natural Resource Conservation District.  Infiltration galleries of Oregon. Washington, D.C.: GPO, 2000.</ref> Since 1996, the Natural Resource Conservation Service in Oregon has installed 22 infiltration galleries, some of which divert as much as 1400 gallons per minute (2.5 cubic feet per second).<ref>Greg Card, Natural Resource Conservation Service, personal communication, 17 October 2001.</ref>
    
====Advantages====
 
====Advantages====
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====Disadvantages====
 
====Disadvantages====
A significant challenge to infiltration galleries in certain streams is preventing the perforated pipes from becoming blocked with fine sediment. Although many infiltration galleries are equipped with a reverse pumping feature to flush out sediments, sediment can still pose problems. Caution must be taken to ensure that pumping rates do not reduce surface flows or water tables to the point of harming aquatic habitat or riparian vegetation. In addition, infiltration galleries will not work at all sites.  Characteristics that could preclude the use of infiltration galleries include:[7]
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A significant challenge to infiltration galleries in certain streams is preventing the perforated pipes from becoming blocked with fine sediment. Although many infiltration galleries are equipped with a reverse pumping feature to flush out sediments, sediment can still pose problems. Caution must be taken to ensure that pumping rates do not reduce surface flows or water tables to the point of harming aquatic habitat or riparian vegetation. In addition, infiltration galleries will not work at all sites.  Characteristics that could preclude the use of infiltration galleries include:<ref>Department of Agriculture, Natural Resource Conservation District. Infiltration galleries of Oregon. Washington, D.C.: GPO, 2000.</ref>
 
   
*“Armored” gravels on the streambed that would indicate poor percolation rates;
 
*“Armored” gravels on the streambed that would indicate poor percolation rates;
 
*Limited thickness or absence of gravel substrate that could prevent the placement of perforated pipes at depths adequate to protect them from scouring;
 
*Limited thickness or absence of gravel substrate that could prevent the placement of perforated pipes at depths adequate to protect them from scouring;
 
*Streambed made up of fine-grained soils such as clays, silts and sands that would continually clog the perforations; and
 
*Streambed made up of fine-grained soils such as clays, silts and sands that would continually clog the perforations; and
*Stream reaches with unstable banks that can migrate significant distances from their original locations, thus separating infiltration galleries from the water source. [8]
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*Stream reaches with unstable banks that can migrate significant distances from their original locations, thus separating infiltration galleries from the water source.<ref>Glenn Ginter, Illinois Valley Soil and Water Conservation District, personal communication, 9 October 2001.</ref>
    
When relying on vertical wells, there is a risk that wells could dewater the stream where the subsurface water is connected to the surface water. This is a growing problem in states, such as California, where groundwater pumping is unregulated.  
 
When relying on vertical wells, there is a risk that wells could dewater the stream where the subsurface water is connected to the surface water. This is a growing problem in states, such as California, where groundwater pumping is unregulated.  

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