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A well designed forebay will also spread the flow somewhat, reducing erosion around the inlet. One effective way of achieving this is by surrounding the pad with some form of level spreader on all sides. The level spreading could be a sharp crested weir in metal or concrete, or be more like a soft edged [[Check dams|check dam]].
A well designed forebay will also spread the flow somewhat, reducing erosion around the inlet. One effective way of achieving this is by surrounding the pad with some form of level spreader on all sides. The level spreading could be a sharp crested weir in metal or concrete, or be more like a soft edged [[Check dams|check dam]].
The required volume for a small forebay serving up to 2 Ha (''V<sub>f</sub>'', m³) may be calculated as:
The required volume for a small forebay, serving up to 2 Ha (''V<sub>f</sub>'', m³), may be calculated as:
<math>V_{f}=A_{c}\times R\times L_{o} \times F_{c}</math>
:<math>V_{f}=A_{c}\times R\times L_{o} \times F_{c}</math>
{{plainlist| 1=Where:
{{plainlist| 1=Where:
*''A<sub>c</sub>'' = The area of the catchment (m²),
*''A<sub>c</sub>'' = The area of the catchment (m²),
*''F<sub>c</sub> = The cleanout frequency (yrs)
*''F<sub>c</sub> = The cleanout frequency (yrs)
}}
}}
The area of the forebay designed for 80 % capture efficiency (i.e. R = 0.8) may be calculated as:
:<math>A_{f}=frac{12 Q}{V}</math>
{{plainlist| 1=Where: