Comparison of storage requirements for two different stormwater harvesting strategies

As stormwater flows are intermittent, the requirement to store urban runoff is important to the design of a stormwater re-use scheme. In many urban areas, the space available to provide storage is limited and thus the need to optimise the storage volume becomes critical. This paper will discuss the advantages and disadvantages of two different approaches of providing storage: 1) a single storage in which stormwater capture and a balanced release for supply use is provided by the one unit and 2) a dual storage in which the roles of stormwater capture and supply release is provided by two separate storage units. The comparison between the two strategies is supported by predictive modelling assessing the supply reliability and storage volume requirements for both options. The results of the comparison provide guidance to the design of more efficient storages associated with stormwater harvesting systems. Introduction The harvesting of stormwater for re-use is becoming recognised as a viable component of sustainable urban water management. The capture, storage, treatment and subsequent use of urban runoff can meet a range of water conservation, water quality and streamflow objectives. Due to these multiple benefits, the widespread drought conditions in recent years and the effectiveness of impervious urban surfaces (roofs, roads and other paved areas) to generate runoff, stormwater re-use systems have been rapidly introduced into Australia. Despite the growing number of re-use schemes, the technology of urban stormwater harvesting can be considered as emerging, compared to alternatives such as seawater desalination and water recycling. More research on developing compact, efficient and reliable stormwater harvesting systems is required to deliver the substantial water resource opportunities of urban runoff. This paper considers ways to improve the efficiency of storing stormwater which is an integral part of any re-use system. Single and Dual Storage Systems The features of stormwater harvesting vary considerably between projects, but a review of existing schemes (DEC NSW, 2006) indicate some common elements including 1) capture collection or diversion of stormwater from the urban drainage system; 2) storage temporary detention of stormwater in tanks or ponds to balance supply and demand; 3) treatment to meet the quality requirements of the use of treated water; and 4) distribution -