Memorandum submitted by Mark Liebman (FW 13)

Mark Liebman is Director of the Sustainability Workshop Ltd.

 

1 I am a Civil and Environmental Engineer with significant drainage design experience, gained largely in Australia where pluvial flooding in urban areas has largely been eliminated through careful systematic design of drainage systems. Australian practice demands management of the whole drainage system (both surface and piped as an integrated system) and I am one of many in thinking the approach has significant merit.

2 I wish to write to express concern with respect to one important aspect of the Floods and Water Bill. I understand that one major objective of the Bill is to establish clear responsibility for the management of flood risk. Establishment of that responsibility must come from an understanding of the causes of flooding. Section 3 (a) quite rightly recognises that flooding from sewerage systems does occur as a result of rainfall however the Bill is likely to fail to establish responsibility for management of flooding from sewerage systems.

3 Specifically my concern relates to the definitions of "surface water" included in Section 6 (5). Section 6(5) defines "surface runoff" as rainwater (including snow and other precipitation) (a) which is on the ground surface, and (b) has not entered a watercourse, drainage system or public sewer.

4 Section 9 and 10 of the Bill proceeds to define key responsibilities: A lead local flood authority will have key responsibilities including the preparation of a local flood risk management strategy for surface runoff, ground water etc.

5 An issue may arise whereby a local area is at significant risk of localised flooding caused by a failure of the drainage system. Failure of the drainage system can occur in several different ways and one of the principle means of failure is by a surcharge of water conveyed inside the piped system back onto the surface water system.

6 Under the proposed Bill, lead local flood authorities will not be responsible for managing this risk. Because it is water that has entered a drainage system it is not defined as a surface water and nor is it groundwater.

7 A key attribute of any effective surface water risk management strategy must be to manage both surface water that is yet to enter the drainage system (this aspect is covered effectively by the Bill) as well as water that has entered the drainage system but which has subsequently been forced out of the drainage system (surcharged) during a rainfall event for one reason or another.

8 In summary my concern is that the proposed Bill will fail to ensure that local surface water management systems are managed as an integrated system. The definitions adopted in the Bill will mean that a significant area of existing flood risk will remain uncontrolled.

 

January 2010