The discharge of surface water from an impermeable area requires consent in accordance with Byelaw 3. The Board will determine applications received seeking to discharge surface water in accordance with the policy below. Applications for consent to discharge surface water run-off into any watercourse within the Board’s Internal Drainage District will be considered against the capacity of the receiving watercourse to accept the proposed surface water flows (rate and volume). To assist in determining the application, the Board may require the applicant to undertake hydraulic modelling work. The requirement for consent to discharge surface water may be waived in writing at the officer’s discretion where the impermeable area is less than 50m2 and is an extension of an existing impermeable area with a satisfactory surface water outfall.  

Policy: Discharge of Surface Water

The Board will only approve an application to discharge surface water where the watercourse can be evidenced as being connected to the wider watercourse network. For systems serving impermeable areas greater than 0.25ha the proposed discharge rate should be no higher than 2/l/s/ha or annual average flood flow rate (QBar or QMed), whichever is higher. Exceptions may be allowable when it is evidenced that to achieve this rate would require a static flow control device (vortex flow control or fixed orifice plate) with an orifice smaller than 50mm* in diameter (or 100mm where debris control is not possible). Systems with a static flow control devices with an orifice smaller than 100mm in diameter should be designed to prevent debris entering the flow control device. Applications may be refused if the Board's Officers consider that the proposals may increase flood risk, cause environmental harm which cannot be mitigated, negatively impact the efficiency of local drainage or if the receiving watercourse will not be capable of accepting the planned additional flows. If consent is granted by the Board, this may be conditional, including the payment of a Surface Water Development Contribution as outlined by the Board’s Development Control Charges and Fees Policy. Notably it is the Board’s preference that systems are adopted by statutory authorities / bodies whenever possible.  

*75mm for the Pevensey and Cuckmere WLMB