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--- stone_outlet_protection [2022/05/06 11:19] – created admin
+++ stone_outlet_protection [2025/09/30 15:18] (current) – admin
@@ Line 1: / Line 1: @@
-====== Stone Outlet Protection ======
+====== Stone Outlet Protection (Riprap) ======
-Stone outlet protection is designed to release water from management practices at non-erosive velocities.  An apron of angular stone is placed at the outlet to prevent erosion by dissipating the energy of water as it flows over.
+Stone outlet protection, or riprap, is designed to release water from management practices at non-erosive velocities.  An apron of angular stone is placed at the outlet to prevent erosion by dissipating the energy of water as it flows over.
 **Advantages**
@@ Line 21: / Line 21: @@
 To determine the necessary length and width of the stone outlet protection, the following equations should be used, respectively:
-[[File:/Images/Stone_Outlet_Protection_Equation.PNG]]
+$$ L=1.7*(\frac{Q}{{D_o}^\frac{3}{2}})+8D_o $$
+$$ W=3*D_o $$
+$$ T=D_{50}*2 $$
-In these equations, L is the apron length (ft), W is the apron width (ft) measured at the end wall, Q is the flow rate (cfs) for a 10-year storm event, and D<sub>o</sub> is the pipe diameter (ft).  The minimum thickness of the riprap apron is determined by multiplying the D<sub>50</sub> by 2.
+where
+L = Apron length (ft)\\
+W = Apron width (ft) at the end wall\\
+Q = Flow rate (cfs) for the 10-year design storm\\
+D<sub>o</sub> = Pipe diameter (ft)\\
+T = Apron thickness (in)\\
+D<sub>50</sub> = Median stone size (in)
 ====Stone====
@@ Line 31: / Line 40: @@
 ===Maximum Velocities for Various D<sub>50</sub> Sizes and Shapes===
-|=Maximum Velocity (ft/sec)|=D<sub>50</sub> Cubical (in)|=D<sub>50</sub> Spherical (in)|
-|10.8|12|14|
+^  Maximum Velocity (ft/sec)  ^  D<sub>50</sub> Cubical (in)  ^  D<sub>50</sub> Spherical (in)  ^
-|9.9|10|12|
+|  10.8  |  12  |  14  |
-|8.8|8|10|
+|  9.9  |  10  |  12  |
-|7.6|6|8|
+|  8.8  |  8  |  10  |
-|6.3|4|6|
+|  7.6  |  6  |  8  |
-|5.0|2|4|
+|  6.3  |  4  |  6  |
+|  5.0  |  2  |  4  |
 A geotextile fabric barrier should be installed underneath the stone to prevent the stone from settling and to prevent erosion of the outlet structure.  Care should be taken during construction to ensure that the fabric is not torn, cut, or punctured.  Any damage should be repaired before proceeding with construction.
 ===Recommended Stone Gradation===
-|=Percent Passing by Weight|=Diameter (in)|
-|100|2 x D<sub>50</sub>|
+^  Percent Passing by Weight  ^  Diameter (in)  ^
-|60-85|1.5 x D<sub>50</sub>|
+|  100  |  2 x D<sub>50</sub>  |
-|25-50|D<sub>50</sub>|
+|  60-85  |  1.5 x D<sub>50</sub>  |
-|5-20|0.5 x D<sub>50</sub>|
+|  25-50  |  D<sub>50</sub>  |
-|0-5|0.2 x D<sub>50</sub>|
+|  5-20  |  0.5 x D<sub>50</sub>  |
+|  0-5  |  0.2 x D<sub>50</sub>  |
+[{{ :wiki:images:correct_riprap.jpeg?direct&600 |Correctly installed riprap at pipe outlet}}]
+[{{ :wiki:images:poorly_installed_riprap.jpeg?direct&600 |Erosion around riprap from improper shaping}}]
 =====Construction=====
@@ Line 57: / Line 72: @@
   *The apron must be at least 1.5 feet below the invert elevation of the outlet structure
-====Manning's "n" Values for Various Rock Sizes====
+**Stone Outlet Protection to a Flat Area (Left) and Well-Defined Channel (Right)**
-|=Diameter (in)|="n" Value|
+{{ :wiki:images:stone_outlet_protection.png?600 |}}
-|2|0.030|
-|4|0.033|
-|6|0.036|
-|8|0.037|
-|10|0.039|
-|12|0.040|
-====Stone Outlet Protection to a Flat Area (Left) and Well-Defined Channel (Right)
-[[File:/Images/Stone_Outlet_Protection.PNG|Source: Adapted from the Georgia Stormwater Manual]]
 =====Maintenance=====
@@ Line 78: / Line 83: @@
 ===References===
-  *[[https://www.nrcs.usda.gov/wps/portal/nrcs/detail/wy/technical/engineering/?cid=nrcs142p2_027269|NRCS Rock Outlet Protection Fact Sheet]]
+  *[[https://efotg.sc.egov.usda.gov/api/CPSFile/31113/468_WI_CPS_Lined_Waterway_or_Outlet_2021|NRCS Conservation Practice Standard 468 - Lined Waterway or Outlet]]