5179Flood Report_REV_3

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Callaghan & Toth

 

3. RATIONAL METHOD FLOWS — PRE DEVELOPMENT

 

ATCHMENT BDY 50m

 

Catchment Area = 1.80 (Pearsons Rd) + 1.47 (Elm St) = 3.27 Ha
C10 Runoff Coefficients: 0.69 (Pearsons Rd) and 0.79 (Elm St)

Concentration Times:

From Elm St: 8m sheet flow @ 1% = 8.0 mins
60 m swale flow @ 1% = 4.0 mins
80 m pipe/path @ 4% @1m/s_ =1.3 mins
57 m pipe/road @ [email protected]/s = 0.7 mins

175 m swale/gully@ 1m/s = 3.0 mins
Total: 17 mins
From Pearsons Rd: 190 m sheet flow @6% = 18mins

Adopt: 18 mins.

Q100 = (0.00278 x 1.20 x 0.69 x 190 x 1.80) + [(0.00278 x 1.20 x 0.79 x 190 x 1.47) — 0.46] = 1.07
m/sec

Q20 = (0.00278 x 1.05 x 0.69 x 148 x 1.80) + [(0.00278 x 1.05 x 0.79 x 148 x 1.47) — 0.46] = 0.58
m°/sec

Q5 = (0.00278 x 0.95 x 0.69 x 120 x 1.80) + [(0.00278 x 0.95 x 0.79 x 120 x 1.47) — 0.46] = 0.39
m/sec

Q1 = 0.00278 x 0.80 x 0.69 x 74 x 1.83 = 0.20 m/sec

 

2035 2 Pearsons Road — Flood Study — Revision 3 April 2021