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Gravel diaphragms are simply gravel filled trenches which act as inlet structures by redistributing concentrated flow to sheet flow: reducing the erosive power of the water and promoting infiltration. They also act as a pretreatment by settling out sediment particles before they reach any downstream structure or practice.  

Gravel diaphragms are simply gravel filled trenches which act as inlet structures by redistributing concentrated flow to sheet flow: reducing the erosive power of the water and promoting infiltration. They also act as a pretreatment by settling out sediment particles before they reach any downstream structure or practice.  

 

{{textbox|Gravel diaphragms are ideal for distributing flow and providing pretreatment for  

{{TextBox|1=Gravel diaphragms are ideal for distributing flow and providing pretreatment for  

*[[Bioretention cells]]  

*[[Bioretention cells]]  

*[[Bioswales]]

*[[Bioswales]]

*[[Enhanced grass swales]]

*[[Enhanced grass swales]]

*[[Vegetated filter strips]]}}

*[[Vegetated filter strips]]}}

 

===Planning considerations===

==Planning considerations==

*Diaphragms can be designed along curves as readily as straight lines,  

*Diaphragms can be designed along curves as readily as straight lines,  

*As they are not a conveyance practice, they should be designed along a single contour line, promoting the level spreading function,   

*As they are not a conveyance practice, they should be designed along a single contour line, promoting the level spreading function,   

*Flow should be directed into the device laterally,

*Flow should be directed into the device laterally,

 

===Design===

==Design==

*Where flow comes off an impervious surface, a drop of 75 mm or more to the surface level of the diaphragm is recommended,

*Where flow comes off an impervious surface, a drop of 75 mm or more to the surface level of the diaphragm is recommended,

*Typical dimensions for the trench excavation are 300 mm deep and 600 mm wide. The trench may be any length,  

*Typical dimensions for the trench excavation are 300 mm deep and 600 mm wide. The trench may be any length,  

*The trench should be lined with geotextile before filling with gravel,   

*The trench should be lined with geotextile before filling with gravel,   

*River rock or decorative aggregate may be included in a layer at the top of the gravel fill, for aesthetic value.  

*River rock or decorative aggregate may be included in a layer at the top of the gravel fill, for aesthetic value.  

 

===Materials===

==Materials==

<h4>Gravel</h4>

<h4>Gravel</h4>

{{:Pea gravel}}

{{:Pea gravel}}

<h4>Geotextile</h4>

<h4>Geotextile</h4>

{{:Geotextiles}}

{{:Geotextiles}}

 

===External Resources===

==External Resources==

*[http://vwrrc.vt.edu/swc/april_22_2010_update/DCR_BMP_Spec_No_2_SHEET_FLOW_Final_Draft_v1-8_04132010.htm VIRGINIA DCR STORMWATER DESIGN SPECIFICATION No. 2]

*[http://vwrrc.vt.edu/swc/april_22_2010_update/DCR_BMP_Spec_No_2_SHEET_FLOW_Final_Draft_v1-8_04132010.htm VIRGINIA DCR STORMWATER DESIGN SPECIFICATION No. 2]

*[https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17751.wba National Engineering Handbook Part 628 Dams Chapter 45 Filter Diaphragms]

*[https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17751.wba National Engineering Handbook Part 628 Dams Chapter 45 Filter Diaphragms]

[[category: pretreatment]]

[[category: pretreatment]]