Design of Rock Chutes per Robinson
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language (en, es)en
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Design of Rock Chutes per Robinson
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Overview:
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Use this method to size the loose angular riprap for a chute/spillway.
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See https://www.fs.fed.us/biology/nsaec/fishxing/fplibrary/Robinson_1998_Design_of_Rock_Chutes.pdf
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Check that the sample values correspond to the example in the reference.
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Instructions:
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1. Use File, Make a copy... or File, Download as... to make this file editable.
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2. Enter slope and flow per meter (foot) in the green cells to get the riprap size you need in the yellow cell.
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3. Note and use the important values in the yellow and red cells.
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4. Contact Tom Haws for help or with feedback or to offer a translation.SIftin
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Input S0, chute slope0.25
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Input qt, total unit flow (m^3/s/m)0.1m^3/s/m1.08ft^3/s/ft
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Input rock specific gravity2.65
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Input gradation standard deviation (D84.1/D50 = D50/D15.9)1.25
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Input np, angular riprap porosity0.45
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Top crest radius = 40 * D50 per Figure 13828.037813mm12.56ft150.7in
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Thickness of rock layer = 2 * D50 per Figure 1191.4018906mm0.63ft7.5in
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Outlet reach length = 15 * D50 per Figure 11435.51418mm4.71ft56.5in
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Is method valid for slope? 0.02 <= S0 <= 0.40?TRUE
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Is method vaild for rock specific gravity? 2.54 <= sg <= 2.82TRUE
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Is method valid for rock gradation distribution? 1.15 <= SD <= 1.47TRUE
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D50,1 (for S0 < 0.10) = (q*S0^1.50/9.76E-7)^(1/1.89) per Eq. 1149mm0.49ft5.9in
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D50,2 (for S0 0.10 <= S0 <=0.40) = (q*S0^-0.58/8.07E-6)^(1/1.89) per Eq. 1
96mm0.31ft3.8in
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D50, median rock size (mm)96mm0.31ft3.8in
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n, Manning roughness = 0.0292 * (D50 * S0)^0.147 per Eq. 70.047
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Vm, velocity through rock mantle = np * (S0 * g * D/4)^0.50.109m/s0.36ft/s
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qm, unit flow through mantle = Vm * 2 * D50 (m^3/s)0.0209m^3/s/m0.22ft^3/s
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qs, surface unit flow = qt - qm (m^3/s)0.0791m^3/s/m0.85ft^3/s
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d, flow depth above effective top of riprap = (n * qs/S0^0.5)^0.6 (m)0.053m0.17ft2.1in
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Notes:
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The equations were developed using a D50 range of 15mm to 278mm rock.
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"The elevation of the top of riprap in the outlet reach should be at or below the downstream channel bed elevation"
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