DESIGN OF SEDIMENT BASIN SECTION 1

STEP 1 Sizing of Sediment Basin

Table 39.4 - Sediment Basin Type

Table 39.5 - Dry Sediment Basin sizing Guidelines

A (catchment area) = 0.401 in hacres

tc = 20 minutes

Required surface area = 100.25 refer table 39.5 ( m2 )

Total volume required = 120 refer table 39.5 ( m3 )

Settling zone reqiured, V1 = 60.15 m3

(half of Total volume)

Settling zone depth, y1 = 1 from table 39.5 ( m )

Try settling zone width, w1 = 7 m

Required settling zone length, L1 = 15 m

Average surface area = 105 m2

> 100.25 OK !

L1 / y1 ratio = 15.00 m < 200 OK !

L1 / w1 ratio = 2.14 m > 2 OK !

STEP 2 Sediment storage zone

Z = 2

Required sediment storage, V2= 60.15 depth storage, d1 = 1

For slide slope, Z = 2(H) : 1(V)

w2 = 5

L2 = 13.0

from equation V2 new = 63 V2 new > V2 OK !

y2 = 7 y2 > 0.3 m OK !

STEP 3 Overall basin dimensions

At top water level

Width, WTWL = 9 m

Length, LTWL = 13 m

Base

Width, WB = -23 m

Length, LB = -15 m

Depth : Settling zone, y1 = 1 m

Sediment Storage zone, y2 = 7 m

Total depth = 8 m

Side Slope Z = 2(H) : 1(V)

STEP 4 Sizing of outlet pipe

Outlet riser : 900 mm dia perforted MS pipe

Average surface area, Aav = 231.000 m2

Orifice area, A total = 0.01 m2

Using An orifice size of 50mm, the area of each orifice is, Ao = 1.96 x 10-3

m2

Ao = 0.00196 m2

Total number of orifice required = A total / 1.96 x 10-3

= 3

STEP 5 Sizing of emergency spilway

Minimum primary outlet diameter = 300 mm

The 10 year ARI rainfall intensity is derived from equation 13.3 and Table 13.3

ln 10

I30 = a + b ln t + c ln (t2) + d ln (t

3) equation 13.2

Pd = P30 - FD(P60-P30) equation 13.3

* Value F D derived from Table 13.3 & Figure 13.3 (Volume 4-MSMAM)

I = Pd/d equation 13.4

Equation 13.3,13.4 & Figure 13.3 for short duration storms (IDF values)

ln 10

I30 = 129.15 mm/hr

Runoff Coefficient, C = 0.84 Post-development (Chart 14.4)

0.77 Pre-development

Q10 = C.10

I30.A /360 equation 14.7

For Post-development, Q10 = 0.12 m3/s

For Pre-development, Q10 = 0.11 m3/s

Qriser = CO AO (2gHO)1/2

CO = 0.6

= 0.93 m3/s

Qspillway = Q10 - Qriser

= -0.81 m3/s

From Equation 20.9, Qspillway = CSP B HP1.5

= 3.95 m3/s

> 2.97 m3/s OK !

Try CSP = 1.7

B = 5 m

HP = 0.6 m

Design Chart 20.2

Total depth including spillway = 8.9 m

DESIGN OF SEDIMENT BASIN SECTION 2

STEP 1 Sizing of Sediment Basin

Table 39.4 - Sediment Basin Type

Table 39.5 - Dry Sediment Basin sizing Guidelines

A (catchment area) = 13.105 in hacres

tc = 30 minutes

Required surface area = 3276.25 refer table 39.5 ( m2 )

Total volume required = 3932 refer table 39.5 ( m3 )

Settling zone reqiured, V1 = 1965.75 m3

(half of Total volume)

Settling zone depth, y1 = 0.6 from table 39.5 ( m )

Try settling zone width, w1 = 40 m

Required settling zone length, L1 = 82 m

Average surface area = 3276.25 m2

> 3276.25 OK !

L1 / y1 ratio = 136.51 m < 200 OK !

L1 / w1 ratio = 2.05 m > 2 OK !

STEP 2 Sediment storage zone

Z = 2

Required sediment storage, V2=V1 = 1965.75 depth storage, d1 = 0.6

For slide slope, Z = 2(H) : 1(V)

w2 = 38.8

L2 = 80.7

from equation V2 new = 2076 V2 new > V2 OK !

y2 = 0.7 y2 > 0.3 m OK !

STEP 3 Overall basin dimensions

At top water level

Width, WTWL = 41 m

Length, LTWL = 81 m

Base

Width, WB = 36 m

Length, LB = 78 m

Depth : Settling zone, y1 = 0.6 m

Sediment Storage zone, y2 = 0.7 m

Total depth = 1.3 m

Side Slope Z = 2(H) : 1(V)

STEP 4 Sizing of outlet pipe

Outlet riser : 900 mm dia perforted MS pipe

Average surface area, Aav = 3064.861 m2

Orifice area, A total = 0.030 m2

Using An orifice size of 50mm, the area of each orifice is, Ao = 1.96 x 10-3

m2

Ao = 0.00196 m2

Total number of orifice required = A total / 1.96 x 10-3

= 16

STEP 5 Sizing of emergency spilway

Minimum primary outlet diameter = 300 mm

The 10 year ARI rainfall intensity is derived from equation 13.3 and Table 13.3

ln 10

I30 = a + b ln t + c ln (t2) + d ln (t

3) equation 13.2

Pd = P30 - FD(P60-P30) equation 13.3

* Value F D derived from Table 13.3 & Figure 13.3 (Volume 4-MSMAM)

I = Pd/d equation 13.4

Equation 13.3,13.4 & Figure 13.3 for short duration storms (IDF values)

ln 10

I30 = 129.15 mm/hr

Runoff Coefficient, C = 0.84 Post-development (Chart 14.4)

0.77 Pre-development

Q10 = C.10

I30.A /360 equation 14.7

For Post-development, Q10 = 3.95 m3/s

For Pre-development, Q10 = 3.62 m3/s

Qriser = CO AO (2gHO)1/2

CO = 0.6

= 0.93 m3/s

Qspillway = Q10 - Qriser

= 3.02 m3/s

From Equation 20.9, Qspillway = CSP B HP1.5

= 4.60 m3/s

> 3.02 m3/s OK !

Try CSP = 1.65

B = 6 m

HP = 0.6 m

Design Chart 20.2

Total depth including spillway = 2.2 m

DESIGN OF SEDIMENT BASIN SECTION 3

STEP 1 Sizing of Sediment Basin

Table 39.4 - Sediment Basin Type

Table 39.5 - Dry Sediment Basin sizing Guidelines

A (catchment area) = 15.575 in hacres

tc = 30 minutes

Required surface area = 3893.75 refer table 39.5 ( m2 )

Total volume required = 4673 refer table 39.5 ( m3 )

Settling zone reqiured, V1 = 2336.25 m3

(half of Total volume)

Settling zone depth, y1 = 0.6 from table 39.5 ( m )

Try settling zone width, w1 = 30 m

Required settling zone length, L1 = 30 m

Average surface area = 900 m2

> 3893.75 OK !

L1 / y1 ratio = 50.00 m < 200 OK !

L1 / w1 ratio = 1.00 m > 2 OK !

STEP 2 Sediment storage zone

Z = 2

Required sediment storage, V2=V1 = 2336.25 depth storage, d1 = 0.6

For slide slope, Z = 2(H) : 1(V)

w2 = 28.8

L2 = 28.8

from equation V2 new = 526 V2 new > V2 OK !

y2 = 0.7 y2 > 0.3 m OK !

STEP 3 Overall basin dimensions

At top water level

Width, WTWL = 31 m

Length, LTWL = 29 m

Base

Width, WB = 26 m

Length, LB = 26 m

Depth : Settling zone, y1 = 0.6 m

Sediment Storage zone, y2 = 0.7 m

Total depth = 1.3 m

Side Slope Z = 2(H) : 1(V)

STEP 4 Sizing of outlet pipe

Outlet riser : 900 mm dia perforted MS pipe

Average surface area, Aav = 787.280 m2

Orifice area, A total = 0.008 m2

Using An orifice size of 50mm, the area of each orifice is, Ao = 1.96 x 10-3

m2

Ao = 0.00196 m2

Total number of orifice required = A total / 1.96 x 10-3

= 4

STEP 5 Sizing of emergency spilway

Minimum primary outlet diameter = 300 mm

The 10 year ARI rainfall intensity is derived from equation 13.3 and Table 13.3

ln 10

I30 = a + b ln t + c ln (t2) + d ln (t

3) equation 13.2

Pd = P30 - FD(P60-P30) equation 13.3

* Value F D derived from Table 13.3 & Figure 13.3 (Volume 4-MSMAM)

I = Pd/d equation 13.4

Equation 13.3,13.4 & Figure 13.3 for short duration storms (IDF values)

ln 10

I30 = 129.15 mm/hr

Runoff Coefficient, C = 0.84 Post-development (Chart 14.4)

0.77 Pre-development

Q10 = C.10

I30.A /360 equation 14.7

For Post-development, Q10 = 4.69 m3/s

For Pre-development, Q10 = 4.30 m3/s

Qriser = CO AO (2gHO)1/2

CO = 0.6

= 0.93 m3/s

Qspillway = Q10 - Qriser

= 3.77 m3/s

From Equation 20.9, Qspillway = CSP B HP1.5

= 3.95 m3/s

> 3.77 m3/s OK !

Try CSP = 1.7

B = 5 m

HP = 0.6 m

Design Chart 20.2

Total depth including spillway = 2.2 m

V1 153.12

Y1 1

W1 8

L1 19.14 19

L1/Y1 19.14 < 200

L1/W1 2.3925 > 2

Y2 0.6

V2 54.2376

d1 1

z 2

w2 6

L2 17.14

W2+L2 23.14

W2L2 102.84

> 51.04 1

2

3