TM 5-814-3/AFM 88-11, Volume III
Choose:
Depth: 10 ft;
Side wall slope: 45 degrees;
Median strip width: 10 ft;
Ditch flat bottom width = rotor length + 1.0 ft = 14 1 = 15 ft;
Ditch width at water surface = 2 x 10 + 15 = 35 ft;
15 % 35
) 10 ' 250 sq ft;
Ditch cross-section area = (
2
Curvature volume = (2)(3.142)(22.5)(250) = 35,325 cu ft (by Theorem of Pappus);
Ditch straight wall volume = 52,125 - 35,325 = 16,800 cu ft;
16,800
' 33.6, or 34 ft;
Total length of the ditch at the waterline =
2 250
Ditch width = 2(35) + 10 = 80 ft;
Total ditch length = 34 + 80 + 114 ft;
Overall ditch dimensions = 114 ft x 80 ft x 10 ft deep.
f.
Final clarifier.
One clarifier required for each ditch unit (Spiraflow clarifier).
Overflow rate # 450 gpd/sq ft;
Detention time = 3 hr;
.05 106
Area required =
1,111sq ft;
1 450
1,111 0.5
Diameter '
' 37.6, use 38 ft;
0.785
Actual area = (38)2 x 0.785 = 1133.5 sq ft;
0.5 106
' 441 gpd/sq ft;
Actual overflow rate =
1133.5
0.5 106 3
' 8356.5 cu ft;
Volume =
24 7.48 1
Straight wall dept = ( 8356.5 ) ' 7.4 ft, use 8 ft;
1133.5
Actual detention time = 8 1133.5 24 7.48/0.5 106 = 3.25 hr.
g. Check for nitrificaiton in oxidation ditch. Find MLVSS concentration required at standard
conditions (20EC, pH8.5) to completely nitrify ammounia shown in figure C-5.
C-27
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