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→Design
[[File:Gravel_diagram.jpg|thumb| 75 mm drop from the impervious surface onto the gravel diaphragm]]
[[File:Gravel diaphragm.png|thumb|Note the fall from the impervious surface to the gravel surface]]
[[File:Gravel diaphragm.png|thumb|Note the fall from the impervious surface to the gravel surface]]
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.
If the contributing drainage area is solely turf (e.g., sports field), then the gravel diaphragms may be eliminated from the treatment train.
If the contributing drainage area is solely turf (e.g., sports field), then the gravel diaphragms may be eliminated from the treatment train.
*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 [[stone]] may be included in a layer at the top of the gravel fill, for aesthetic value.
==Materials==
==Materials==
===Gravel===
The type of medium sized aggregates recommended for gravel diaphragms are described in [[choker layer]]. In some contexts it may be desirable to apply a surface layer of more decorative [[stone]].
===[[Geotextiles]]===
===Geotextiles===
{{:Geotextiles}}
{{:Geotextiles}}
*[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]
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[[category: pretreatment]]
[[category: pretreatment]]