Describe briefly the purpose of stormwater storage. Illustrate your answer by reference to an annotated catchment hydrograph. A developed site within a 4 ha catchment area has a single point discharge, without attenuation, to an adjacent watercourse. It is proposed to retrofit an end of line attenuation tank to the storm outfall such that the outflow for a 10 year return storm is limited to the mean annual maximum flow generated by the pre- developed greenfield site. Calculate the mean annual maximum flow generated by the pre-developed greenfield site using the 3 parameter Institute of Hydrology (IoH) runoff equation and hence determine the required attenuation tank volume by assessing the site for storm durations of 1, 4 and 8 hours. The following greenfield site parameters apply:- Standard Average Annual Rainfall (SAAR) 933 mm Soil Index (SOIL) 0.36 Use the Bilham formula to calculate rainfall intensities, assume the volumetric runoff coefficient for the impermeable area, C, 0.75 and take the impermeable area of the developed site as 75% of catchment area. = Briefly outline the objectives of Sustainable Urban Drainage Systems (SUDS). Describe two examples of SUDS and explain how each of these might assist in reducing the attenuation tank volume calculated in 1.b) above.