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Case study: Sustainable Flood Risk Management
Catchment Flood Management Plans - Example of the Test and Itchen CFMP
What are CFMPs?
CFMPs are high level plans implemented in order to develop
sustainable flood risk management at catchment scale.
The Test and Itchen CFMP study area – Key facts
Surface: 1735 km2
Rivers Mouth: Totton, Southampton
Mostly rural catchment
Geology: 80% chalk, with tertiary deposits downstream
Classic chalk rivers (groundwater-fed)
High water quality
One of the aims of the first stage of the CFMP is to develop an understanding of the flood generating process
and the extent of current flood risk within the catchment (where risk is the product of consequences and
probability and involves assessment of vulnerability and hazard). Note: CFMPs exclude analysis of tidal
flooding (which is studied in Shoreline Management Plans and/or estuary strategy studies).
Question 1: With reference to the key facts above, what knowledge and skills do you already possess that
could be used in undertaking a CFMP?
Question 2: Using your current knowledge, what processes do you think may contribute to flood risk in
the Test and Itchen catchment?
The Environment Agency use the following set of six generic policy responses to flood risk:
1) No active intervention (including flood warning and maintenance), continue to monitor and advise
2) Reduce existing flood risk management actions (accepting that flood risk will increase with time)
3) Continue with existing or alternative actions to manage flood risk at the current level (accepting that flood
risk will increase over time from this baseline)
4) Take further action to sustain the current scale of flood risk into the future (responding to the potential
increases in flood risk from urban development, land use change, and climate change)
5) Take further action to reduce flood risk (now and/or in the future)
6) Take action to increase the frequency of flooding to deliver benefits locally or elsewhere, (which may
constitute an overall flood risk reduction, e.g. for habitat inundation)
The CFMP process should identify which of the above policies are most applicable to a set of defined
geographical areas called policy units within the catchment. During the process of policy development it is
important to identify opportunities and constraints from flooding at the catchment scale (concerning land
management, floodplain storage, flood defences, etc).
Question 3: Using the list of processes developed for Question 1, complete a table which identifies some of
these opportunities and constraints.
Question 4: What types of information do you think you would require to better identify opportunities
and constraints within the catchment?
Question 5: How would you structure a study which would lead to the selection of specific flood risk
management policies for the Test and Itchen catchment?
www.halcrow.com/software
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ICE/Environment Agency Employers’ Forum – Provision of Teaching Material
CFMPs are developed by the Environment Agency and civil engineering consultancies, such as Halcrow, may
be employed to undertake the studies. The Agency seeks to work with key decisions makers within the
catchment to identify policies: use is made of steering groups and consultation.
Question 6: Who do you think would be relevant to be involved in the consultation process? How would
you involve these people/organisations and what would you expect from them?
The function of modelling in CFMPs
Some models have been built during previous studies for some reaches of the Test and Itchen rivers and their
tributaries. Very detailed hydraulic models are available for the Andover area and Romsey area. Broad scale
models (combining hydrological and routing models) are available for the Monks Brook, downstream tributary
of the river Itchen running through tertiary deposits; and for the river Itchen itself. Hydrological models tend to
convert rainfall into river flows while hydraulic models route flows down river systems and calculate flows and
water levels at specific locations. Routing models use simplified equations to route hydrographs down long
lengths of rivers and floodplains and tend to not predict water levels.
Question 7: Do you think hydraulic, rainfall-runoff and flow routing modelling could help the study? If
so, how would you use these tools (make reference to the cost of modelling compared with the value of
new information obtained through modelling).
Overview map of the Test and Itchen catchment
More information on the catchment and CFMPs can be found at:
www.environment-agency.gov.uk (Regions > Southern Region > Hampshire and Isle of Wight > River Test / Itchen)
www.defra.gov.uk
www.halcrow.com/software
v2 13/01/2006 JMW