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Stage 2: Fieldwork

The risk of flooding | The impact of flooding | The management of flooding

The risk of flooding

(i) Choosing a suitable site

• Select a study area which experiences flooding issues.
• Place a grid over a map of your study area to divide it into smaller squares.
  
  As a rough guide, aim for at least 200 squares (approximately 50m x 50m each). It is essential that you have an even number of survey squares on and off the floodplain.

(ii) Measuring flood likelihood

The likelihood that any particular site will be flooded by a river depends on many factors. The two most straightforward factors to measure in the field are

1. Height of land above sea level. This data can be obtained from a large scale map or you can use a GPS altitude readings taken several times in each square. Some in-car sat-nav devices may be able to give you the altitude data. Put the raw data into categories (as in the table). The exact height bands that you choose will be specific to the site.

Score	Height (m)
5	49 - 53
4	54 - 58
3	59 - 63
2	64 - 68
1	69+

2. Distance from river - use pacing or a trundle wheel to measure the shortest distance between the centre of the square and the edge of the river. For squares where this is not possible, measure the distance on a map. Put the raw data into categories (as in the table). The exact height bands that you choose will be specific to the site.

Score	Distance (m)
5	0 - 49
4	50 - 99
3	100 - 149
2	150 - 199
1	200+

Find the mean of the two likelihood scores. This will give you an index of flood likelihood for each square of between 1 and 5.

(iii) Measuring flood severity

There are two ways in which you can measure flood severity: either by mapping land use or by calculating an index of severity.

Method 1: mapping land use

Devise a set of appropriate categories for land use. This could be based on an earlier pilot study and will be specific to the town / area that you are working in.

Record the dominant land use in each survey square.

Example land use categories:

Pre War Low Cost Housing	Industry
Pre War High Cost Housing	Transport
Post War Low Cost Housing	Car Parks
Post War High Cost Housing	Open Space
Retail / Admin - High Order	Agriculture
Retail / Admin - Low Order	Community Services

Method 2: calculating an index of flood severity

The basic idea behind this method is that the same level of flooding will cause more damage in some places (e.g. a hospital) than in others (e.g. a public park). The two most straightforward factors to measure in the field are

1. Percentage of 'built up land' - estimate the percentage of land covered by buildings in each survey square. Put the raw data into categories (as in the table). The exact % built-up land bands that you choose will be specific to the site.

Score	% built-up land
5	80 - 100
4	60 -79
3	40 -59
2	20 -39
1	0 - 19

2. Land use (potential economic loss) - record the dominant land use for each survey square.

Score	Description of land use
5	High-status retail (e.g. department stores); High-tech industry; Offices.
4	High value housing; Low-order retail. Possibly small-scale industry / cafes / pubs.
3	Middle value housing; Community services; Small independent retail stores.
2	Low value housing; Small convenience stores; Small independent garages; Storage facilities / warehouses.
1	Open space (e.g. car parks, derelict land, parks, allotments).

Find the mean of the two severity scores. This will give you an index of flood severity for each square of between 1 and 5.

The impact of flooding

This is more difficult to collect quantitative information. Data allowing you to compare the cost of home insurance of properties at risk of flooding is unobtainable, for reasons of commerical confidentiality. Data on house prices inside and outside areas of flood-risk cannot easily be obtained and may well be of limited value - the risk of flooding is just one of the many factors (such as number of bedrooms, size of garden and perceived desirability of the neighbourhood) which affect house prices.

As an alternative, you can collect information on local people's perceptions of the flood risk in their area. Search for locally made videos on Youtube (many videos of the summer 2007 floods in Yorkshire and the West Midlands have been posted, for example), explore the photographs which people have taken of the local area on Flickr and Geograph, and use social networking sites (such as Myspace) and/or blogs to collect more opinions.

The management of flooding

Before you evaluate the success of measures taken to manage flooding, you need to find out what measures are taken! Although some of them will be obvious (e.g. concrete walls lining the banks of some rivers) many of them (such as land-use zoning) are not.

Choose a short stretch of river (maybe 2km) which runs through an urban area. Use local sources (such as a local authority or Environment Agency River Catchment plan - use an internet search engine to search for "Catchment Management Plan" plus the name of the river). Try to list all the river management techniques being used and, if possible, the length of river frontage that they protect.

One way in which you can carry out a qualititative survey of river management which generates numerical data which can be used in statistical tests is the bi-polar survey.

A number of criteria are chosen which each stretch in a spectrum from extremely positive to extremely negative. A pilot survey in two or three locations will help to show whether your criteria are appropriate for the actual location that you are investigating.

Find the total of all the negative scores and all the positive scores for each survey point. One way of displaying the results of the bi-polar analysis is to construct a modified bar chart with the bipolar score on the x-axis.

Negative factors	-3	-2	-1	1	2	3	Positive factors
Vulnerable to overtopping							Effective against overtopping
Ugly							Enhances natural environment
Prevents public access to river							No limit on public access to river
Disturbs processes of erosion and deposition							No disturbance to processes
High maintenance / operational costs							Low maintenance / operational costs

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