| The side slopes should be no steeper than 1:3 to permit vegetation stabilization and access for maintenance and amenity. This may be relaxed where the pond area is very shallow (0.5 m). stepped or benched slopes are also a possibility, but consideration should be made of maintenance access. <ref>Ballard, B. W., Wilson, S., Udale-Clarke, H., Illman, S., Scott, T., Ashley, R., & Kellagher, R. (2015). The SuDS Manual. London.</ref> | | The side slopes should be no steeper than 1:3 to permit vegetation stabilization and access for maintenance and amenity. This may be relaxed where the pond area is very shallow (0.5 m). stepped or benched slopes are also a possibility, but consideration should be made of maintenance access. <ref name=Ballard>Ballard, B. W., Wilson, S., Udale-Clarke, H., Illman, S., Scott, T., Ashley, R., & Kellagher, R. (2015). The SuDS Manual. London.</ref> |
| A detention time of 24 hours should be targeted in all instances. Where this necessaitates a very low outflow, a [[Flow control#Vo|vortex valve or similar is recommended over an orifice or pipe restiction. The detention time is approximated by the drawdown time. | | A detention time of 24 hours should be targeted in all instances. Where this necessaitates a very low outflow, a [[Flow control#Vortex valve|vortex valve]] or similar is recommended over an orifice or pipe restiction. The detention time is approximated by the drawdown time. |
| The drawdown time in the pond can be estimated using Equation 4.10. Equation 4.10 is the classic falling head orifice equation which assumes a constant pond surface area. This assumption is generally not valid, and a more accurate estimation can be made if Equation 4.10 is solved as a differential equation. This is easily done if the relationship between pond surface area and pond depth is approximated using a linear regression. | | The drawdown time in the pond can be estimated using Equation 4.10. Equation 4.10 is the classic falling head orifice equation which assumes a constant pond surface area. This assumption is generally not valid, and a more accurate estimation can be made if Equation 4.10 is solved as a differential equation. This is easily done if the relationship between pond surface area and pond depth is approximated using a linear regression. |