flood risk assessment in connection with a planning - Breckland ...

Flood Risk Assessment Tesco Supermarket, Swaffham
2.5 Hydrogeology
The Environment Agency online indicative aquifer mapping and the
Landmark Aquifer Designation Mapping identifies that the solid geology
beneath the site is identified as a Principal Aquifer with the superficial
deposits classified as Unproductive Strata.
Principal Aquifers are classified as layers of rock or drift deposits that
have high intergranular and/or fracture permeability - meaning they
usually provide a high level of water storage. They may support water
supply and/or river base flow on a strategic scale. In most cases,
principal aquifers are aquifers previously designated as major aquifer.
Unproductive Strata is classified as rock layers or drift deposits with low
permeability that has negligible significance for water supply or river
base flow.
The subject site is located within an Environment Agency Source
Protection Zone 3 (SPZ3) „Source Catchment Protection Zone‟.
A Source Catchment Protection Zone is defined as the area around a
source within which all groundwater recharge is presumed to be
discharged at the source. In confined aquifers, the source catchment
may be displaced some distance from the source. For heavily exploited
aquifers, the final Source Catchment Protection Zone can be defined
as the whole aquifer recharge area where the ratio of groundwater
abstraction to aquifer recharge (average recharge multiplied by outcrop
area) is >0.75.
The Landmark Aquifer Designation Mapping is reproduced for
reference in Appendix D.
2.6 Hydrology
There are no watercourses within 1km of the site, although there are a
number of small surface water ponds, the closest being a natural pond
and several man made balancing/drainage ponds situated some 100m
to the north of the site. There are further natural surface water ponds to
the east of the site (including Northwell Pond approximately 250m to
the east).
The following hydrological catchment characteristics have been
obtained from Flood Estimation Handbook (FEH) CD –
Page 3
Jubb Consulting Engineers Limited February 2012
P9632-G300C-Rep-120209-MH