Manual Calculation

 

 

The result of computation using MSMAware was checked using spreadsheet in this section

 

1. Determination design storm inflow for the catchment 

 

The aim is to reduce the post-development peak flows for the minor and major system ARI to less than or equal to the pre-development peaks. The minor and major system design storms are 5 year and 50 year ARI, respectively in accordance with Table 1.1. The design storm for the secondary outlet spillway is 100 year ARI. Table 7.1 show Pre and Post development of hydrograph.

 

Table 7.1 Pre and Post Development Hydrograph

2. Preliminary estimation of the required storage volume

 

A preliminary estimate of the required basin volume can be made using the following equation for the major design storm ARI.

           Equation 7.1

where:

Vs = Estimated storage volume (m3)
Vi = Inflow hydrograph runoff volume (m3)
Qj = Inflow hydrograph peak flow rate (m3/s)
Qo = Allowable peak outflow rate (m3/s)
ti = Time base of the inflow hydograph (min)
tp = Time to peak of the inflow hydrograph (min)

 

The basin volume is estimated for each basin inflow hydrograph as shown in Table 7.2 and maximum value selected.

Table 7.2 Preliminary Estimation Basin Volume

Figure 7.1 Graph of Basin Volume Estimation versus Storm Duration

3. Determine Stage Storage Discharge Relationship  

Table 7.3 Basin Stage Storage Data

Figure 7.2 Graph of Storage versus Stage

Table 7.4 Basin stage discharge data

Figure 7.3 Graph of discharge versus stage

4. Storage Routing

Table 7.5 result of routing through the detention basin (50 year ARI, 10 min)

Figure 7.4 Basin inflow and outflow hydrographs for the critical 5year ARI 10 min storm

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