Changes

Check dams are small dams or weirs constructed across a drainage ditch, swale, or channel to lower the speed of concentrated flows for a certain design range of storm events and to promote infiltration.  

Check dams are small dams or [[weirs]] constructed across a drainage ditch, swale, or channel to lower the speed of concentrated flows for a certain design range of storm events and to promote infiltration.  

{{Textbox|1=Check dams:

{{Textbox|1=Check dams:

*may be constructed of any resilient and waterproof material, including: rock gabions, earth berms, coarse aggregate or rip-rap, concrete, metal or pre-treated timber. Rocks used in check dams should have median diameter 25 - 75 mm.  

*may be constructed of any resilient and waterproof material, including: rock gabions, earth [[berms]], coarse aggregate or rip-rap, concrete, metal or pre-treated timber. [[Stone]] used in check dams should have minimum median diameter 25 - 75 mm.  

*for enhanced swales may be up to 0.6 m in height; the maximum design depth of ponded water should be ≤ 0.6 m.

*for enhanced [[swales]] may be up to 0.6 m in height; the maximum design depth of ponded water should be ≤ 0.6 m.

*designed for higher flow velocities should have spillways incorporated into their profile, to direct water to the centre of the swale.  

*designed for higher flow velocities should have spillways incorporated into their profile, to direct water to the centre of the swale.  

*are usually installed between 10-20 m along the swale. The spacing of dams should not exceed the horizontal distance from the toe of the upstream dam to the same elevation on the downstream dam.  

*are usually installed between 10 - 20 m along the swale. The spacing of dams should not exceed the horizontal distance from the toe of the upstream dam to the same elevation on the downstream dam.  

*should have energy dissipation and erosion control measures installed in the 1 - 2 m  downstream. Examples include large aggregate or [[Turf reinforcement|turf reinforcement]]}}

*should have energy dissipation and erosion control measures installed in the 1 - 2 m  downstream. Examples include large aggregate or [[Turf reinforcement|turf reinforcement]]}}

#The gradient between the top of the lower check dam and the bottom of the upper one is called "compensation gradient" which is the future or final effective gradient of the swale. It is formed when material carried by flowing water fills the check dams to spillway level.  

#The gradient between the top of the lower check dam and the bottom of the upper one is called "compensation gradient" which is the future or final effective gradient of the swale. It is formed when material carried by flowing water fills the check dams to spillway level.  

#Dams are usually installed between 10-20 m along the swale. The spaces between check dams can be determined according to the compensation gradient and the effective height of the dams. They are distributed such that the crest of each dam is at approximately the same elevation as the toe of the upstream dam. If the slope along the swale varies, so should the distance between the dams.

#Dams are usually installed between 10-20 m along the swale. The spaces between check dams can be determined according to the compensation gradient and the effective height of the dams. They are distributed such that the crest of each dam is at approximately the same elevation as the toe of the upstream dam. If the slope along the swale varies, so should the distance between the dams.

#The compensation gradient of enhanced swales must be < 1 % (0.5% preferred).

#The compensation gradient of enhanced swales must be < 1 % (0.5 % preferred).

The objective of these design recommendations are to maximize the distribution of ponded water along the whole BMP. Detailed design may require iteration of the dam heights and distances along each section of a long swale.

The objective of these design recommendations are to maximize the distribution of ponded water along the whole BMP. Detailed design may require iteration of the dam heights and distances along each section of a long swale.

To estimate the depth of water that can be infiltrated into a surface within a given time:  

To estimate the depth of water that can be infiltrated into a surface within a given time:  

<math>y=f\times t</math>

<math>y=f'\times t</math>

   

   

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''S_i'': Initial existing slope ratio of the swale (rise/run)

*''S_i'': Initial existing slope ratio of the swale (rise/run)

*''S_e'': Desired effective slope of the enhanced swale (between 0.005 - 0.01, rise/run)

*''S_e'': Desired effective slope of the enhanced swale (between 0.005 - 0.01, rise/run)

*''h'': The average effective height of the check dams in m (excluding foundations)}}

*''h'': The average effective height of the check dams in m (excluding foundations)(suggest you use ''y'', calculated above)}}

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*The first check dam should be constructed on a stable point in the gully such as a rock outcrop, the junction point of the gully to a road, the main stream or river, lake or reservoir.  

*The first check dam should be constructed on a stable point in the gully such as a rock outcrop, the junction point of the gully to a road, the main stream or river, lake or reservoir.  

[http://www.fao.org/docrep/006/ad082e/AD082e02.htm FAO]

[http://www.fao.org/docrep/006/ad082e/AD082e02.htm FAO]

[[Category:Modeling]]

[[Category:Calculations]]