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Wallingford HydroSolutions Ltd

Peak flow estimation using the Flood Estimation Handbook statistical

methods and subsequent scientific advances

WINFAP-FEH 3™

The industry-standard design flood estimation software in the UK

User guide

Cover photographs (clockwise from top left):

Scott Leman, Anthony Hall, Ronald Hudson

– Fotolia.com

Design: platform1design.com

WINFAP-FEH 3™

Design flood modelling software

User guide November 2009

Wallingford HydroSolutions Ltd

Maclean Building, Crowmarsh Gifford,

Wallingford OX10 8BB

www.hydrosolutions.co.uk

WINFAP-FEH 3™ User guide

© Wallingford HydroSolutions Ltd. 2009.

All rights reserved. No part of this

publication may be reproduced or

transmitted in any form or by any

means, electronic or mechanical,

including, without limitation, photocopy,

scanning, recording or any information

storage and retrieval system, without

permission in writing from Wallingford

HydroSolutions Ltd.

This software manual has been prepared

by Wallingford HydroSolutions Ltd with

all reasonable skill, care and diligence.

This document has been prepared with

the purposes of enabling you to operate

the software and providing you with

an overview of the methods deployed

within the software. You are responsible

for the interpretation of the information

presented within this manual and formal

training in the use of the methods is

strongly recommended. In no event will

Wallingford HydroSolutions Ltd be liable

to you for any damages, including lost

profits, lost savings or other incidental or

consequential damages arising on your

use of the information in this manual

even if we have been advised of the

possibility of such damages.

Development team

Wallingford HydroSolutions Ltd (WHS)

Software development team are

responsible for the development of the

WINFAP-FEH 3™ software.

Technical specification

Minimum recommended specification

Base computer Intel or equivalent PC

with 8x CD drive (ATAPI compliant)

Processor Pentium IV 1.2 GHz

RAM 512Mb

Free drive space 200 Mb

Monitor Equivalent to XGA: 1024 x

768 at 16 bit 256 colours

Operating system Microsoft Windows

2000, XP or Vista

*Indicative of initial requirement only, the

free drive space required depends on

the installation and the number of time-

series loaded by User.


The use of the WINFAP-FEH 3™ software is governed by the terms and conditions

of the licence agreement between Wallingford HydroSolutions Ltd and the User.

The User is required to accept the licence terms and conditions of use prior to

installation and at runtime. These terms and conditions can be viewed within the

software and are repeated in the following section. Your attention is particularly drawn

to clauses relating to your responsibilities and licence termination.

WINFAP-FEH 3™ software licence terms and conditions

This software licence agreement is a legal agreement between you and

Wallingford HydroSolutions Ltd. Please read it carefully before starting

the software installation process and using the software. It provides a licence

to use the software and contains warranty information and liability

disclaimers. By installing and using the software, you are confirming your

acceptance of the software and agreeing to become bound by the terms of

this agreement. If you do not agree to be bound by these terms set out

here, do not install the software and return the software in its entirety to

Wallingford HydroSolutions Ltd.

NOTE: In this agreement ‘you/yours’ refers to you, the Licensee and ‘we/us/ours’

to the Licensors (Wallingford HydroSolutions Ltd); ‘the software’ to the

WINFAP-FEH 3™ package which comprises the executable program files, databases,

data, documentation, licence protection dongle and installation files provided in

any electronic or hardcopy form.

We provide the software and we hereby license you to use it. You are responsible for

how you use the software to achieve the results you intend, for the results obtained

and how they are used.

Terms and conditions 1 The software is the proprietary product of Wallingford HydroSolutions Ltd and NERC

(CEH) and thus protected by Copyright Law. We reserve all rights of ownership and copyright in the software. Copyright and legal title in the software and legal rights thereto vest in Wallingford HydroSolutions Ltd and NERC (CEH).

2 In consideration of the licence fee paid (if any) we grant you a personal, non-exclu-sive, non-transferable licence to use the software.

3 You may3.1 Install and use the software on an unlimited number of computers in offices

within one postcode location and we reserve the right to check this. 3.2 Make full or partial copies of the installed part of the software for back-up

purposes only, provided you label such copies clearly with our name, the name


of the software and the date of your licence.3.3 Transfer the software and this licence permanently to another party but only

if you obtain our prior written approval and provided the other party signs a new licence agreement with us. Any such transfer terminates your licence agreement.

4 You may not4.1 Make full or partial copies of the installed software for purposes other than

back-up.4.2 Make copies of the source installation optical media.4.3 Transfer, assign, rent, lease, sub-license, sell, give or otherwise dispose of this

software except as stated in the licence.4.4 Reverse compile, disassemble, or otherwise reverse engineer the whole or part

of the software.4.5 Perform bulk data extraction.4.6 Transfer, assign, rent, lease, sub-license, sell, give or otherwise dispose of

any software or data product whose production has involved the use of the software.

4.7 Modify, adapt or translate the software in anyway.4.8 Merge the whole or part of the software with any other software other than

that strictly required by the operating system of the computer on which you have installed it.

4.9 Reproduce, distribute or alter the software documentation.4.10 Export or re-export the software without the appropriate United Kingdom or

foreign government licences.4.11 Reveal the source code or data (if supplied) to a third party. If you do any of the foregoing without our express permission, this agreement

will be breached and your licence automatically terminated. Such termination shall be in addition to and not in lieu of any other legal remedies available to us.

5 Your responsibilities5.1 You are responsible for installing and commissioning the software onto your

computer system unless we have agreed in writing to do so.5.2 You must ensure that proper security precautions are followed to secure the

media on which the software was supplied, the licence certificate and licence protection dongle; these are valuable and proof of your right to use the software.

5.3 Unless otherwise agreed in writing, you must train your staff that use this software to understand its purpose, operations, and limitations.

5.4 You are responsible for how you use the software and the results obtained.5.5 You are responsible for the interpretation of the results produced by the

software.


5.6 You must include the following copyright statement on results produced by the software, including but not limited to images: ‘© Wallingford HydroSolutions Ltd and NERC (CEH). 2009.’

5.7 You must treat this software and its documentation as confidential. You must not disclose any part of it to another party without our permission, even after the licence has been terminated.

6 Term6.1 You are licensed to use the software to the date of expiry stated on

xthe Licence Certificate (inclusive) subject to clause 6.4.6.2 You may terminate your licence and this agreement at any time by

returning it to us together with the original media, the licence dongle and licence certificate.

6.3 This licence will terminate immediately if you fail to comply with any term or condition of this agreement.

6.4 In the case of leased software, this licence will terminate immediately if you fail to make payments in accordance with the payment schedule specified on the Licence Certificate

In the event of any termination you must destroy all full or partial copies of the software resident on your computer system(s) in any form and you agree to provide us on request a written certificate of such destruction.

7 Warranty Subject to clause 7.2, we warrant that for a period of 6 months from the date of

your purchase of the software (‘the Warranty Period’):7.1 The medium on which the software is recorded will be free from defects in

materials and workmanship under normal use. 7.2 The copy of the software in this package will materially conform to the

documentation that accompanies the software. If the software fails to operate in accordance with this warranty, you may, as your sole and exclusive remedy, return the software and the documentation to us during the warranty period, along with dated proof of purchase, specifying the problem, and we will provide you either with a new version of the software or a full refund (at our option).

7.3 We shall not be liable under the warranties given in clause 7.1 above if the software fails to operate in accordance with the said warranty as a result of any modification, variation, or addition to the software not performed by us or caused by any abuse, corruption or incorrect use of the software, including use of the software with equipment or other software which is incompatible.

If you have purchased an extended support and maintenance under a support and maintenance agreement we will provide you with the services as specified in your support and maintenance agreement.


8 Disclaimer8.1 We do not warrant that this software will meet your requirements or that

its operation will be uninterrupted or error free. We exclude and hereby expressly disclaim all expressed and implied warranties or conditions not stated herein (including without limitation), loss of profits, loss or corruption of data, business interruption or loss of contracts; so far as such exclusion or disclaimer is permitted under the applicable law. This Agreement does not affect your statutory rights.

9 Liability9.1 Our liability to you for any losses shall not exceed the amount you originally

paid for the software.9.2 In no event will we be liable to you for any indirect or consequential damages

even if we have been advised of the possibility of such damages. In particular, we accept no liability for any programs or data made or stored with the software nor for the costs of recovering or replacing such programs or data.

9.3 You hereby acknowledge and agree that the limitations contained in this clause are reasonable in light of all the circumstances.

10 The licence protection dongle10.1 In the event of damage to, or malfunction of the licence dongle we will

replace the dongle subject to the original dongle being returned, at your cost, to ourselves prior to dispatch of a replacement dongle. For avoidance of doubt, we will not supply a replacement licence protection dongle if the original dongle cannot be returned to ourselves.

10.2 In the event of accidental damage we will reserve the right to charge you an administration fee for the supply of a replacement licence dongle.

11 General Should any of the provisions in this Licence Agreement be ruled invalid under any

law or Act of Parliament, they shall be deemed modified or omitted only to the extent necessary to render them valid and the remainder of the Agreement shall be upheld.

12 Governing lawThis Agreement is subject to the jurisdiction of the English Courts.


Contents

1 Overview 102 Appropriate use 133 Background 144 Outline 15 4.1 Definitions and conventions 5 Using the WINFAP-FEH 3™ software 16 5.1 Installation 5.1.1 How to install 5.1.2 Licence management 5.2 Login window 5.3 Main window 5.4 General tips 6 Creating a project 24 6.1 Station details window 7 Choice of analysis method 278 Single Site Analysis 28 8.1 Estimating QMED 8.1.1 Estimating QMED in gauged urbanised catchments 8.2 Constructing a flood growth curve 8.3 Obtaining the flood frequency curve 9 Pooled Analysis 33 9.1 Estimating QMED 9.1.1 Calculating QMED from observed data 9.1.2 Estimating QMED from catchment descriptors 9.1.3 Estimating QMED by data transfer 9.1.4 Estimating QMED in ungauged urbanised catchments 9.2 Defining a pooling group 9.2.1 Pooling group details window 9.2.2 Reviewing and adapting pooling groups 9.3 Constructing a flood growth curve 9.4 Obtaining the flood frequency curve 10 Tabulation of menus and sub-menus 4511 Glossary 4812 References and further reading 51


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1 Overview

In the UK the Flood Estimation Handbook (FEH) developed at the Centre

for Ecology and Hydrology (CEH) is recognised as the best practice

method for estimating peak flood flows from flood data. The FEH

statistical methods for flood estimation are based on flood frequency

curves which define a relationship between the size of a flood (peak flow)

and the return period (expected frequency of occurrence).

WINFAP-FEH 3™ was released on 9 September 2009. WINFAP-FEH 3™

is a software package maintained and developed by Wallingford

HydroSolutions Ltd (WHS) that implements a range of statistical analyses

tools from Volume 3 of the FEH. The package is linked to the FEH flood-

peak dataset, which is automatically installed with the software.

WINFAP-FEH 3™ provides Users with an ability to conduct both Single Site

and Pooled Analysis of flood-peak data using Annual Maximum (AM)

data and Peaks Over Threshold (POT) data sets.

Supplementing WINFAP-FEH 3™ is the ReFH software, a rainfall-runoff

modelling package for estimating design flood hydrographs and analysis

of observed events. This provides a temporally-varying design flood flow

(rather than a single peak flow value) following guidance in the FEH

Volume 4 and Supplementary Report No 1.

WINFAP-FEH 3™ includes significant improvements over previous versions.

These are detailed below, and include scientific advances as developed by

Kjeldsen et al. (2008) and Kjeldsen (2009), and improvements to

the functionality.

Scientific advances

Enhanced Single Site Analysis

The new FEH statistical procedures have two different methods for

weighting each member of the pooling group. If the target site has a

gauged record, a higher weighting is given to this; if the site is urban

or ungauged, the weightings are determined solely by similarity index.

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Improved estimation of QMED from catchment descriptors

The equation used to estimate QMED from catchment descriptors

has been improved through detailed analysis, including a measure of

floodplain extent utilising a new catchment descriptor.

Updated QMED adjustment from donor gauges

The equation used to adjust QMED at the ungauged site using data

from a gauged record has been improved. This functionality is now

incorporated into WINFAP-FEH 3™.

New catchment descriptors (FPEXT, CENTROID)

New catchment descriptors have been developed for use in the

new methods, and all are available from FEH CD-ROM 3. Two new

catchment descriptors are used in WINFAP-FEH 3: floodplain extent

(FPEXT) is used in the pooling group development, while the suitability

for donor adjustment of QMED is determined by proximity as

measured using the catchment centroid (CENTROID).

Enhanced pooling procedures

A new procedure has been implemented for development of the

pooling group. The more detailed procedure no longer relies on

pooling-group ranking, but calculates separate weighting equations

for second and third order L-moments, based on record length and

similarity to the target catchment.

Recommended pooled record length

Updated recommendations for the record length advise that a

standard 500 years is used regardless of the target return period.

WINFAP-FEH 3™ implements this protocol as standard practice, but

with the flexibility to change the record length if required by the User.

New urban adjustment method

Further work undertaken by Kjeldsen (2009) has updated the urban

adjustment methods. These are available together with the existing

methods in WINFAP-FEH 3™.

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User-interface improvements

Licensing via USB ‘dongle’

WINFAP-FEH 3™ will be licensed using a USB ‘dongle’, allowing greater

flexibility to the User and a simpler installation process.

Intuitive and User-friendly menus

WINFAP-FEH 3™ has been overhauled to provide a User-friendly

interface and more logical menu structures. The software is much

easier to use as a result.

Improved pooling group-development and flood frequency

curve wizard

The pooling-group wizard has been developed to provide simple

options to implement the new pooling-group methodology. Pooling-

group forms provide enhanced comparison of catchment descriptors

and flood data.

Full integration with forthcoming FEH CD-ROM 3

The standard catchment descriptor file for transferring information

from the FEH CD-ROM 3 has been updated to include the new

catchment descriptors, taking the form of a CD3 file.

Calculator tool for estimating flood characteristics

A calculator allows easy determination of return period for a specific

peak flow, and vice versa.

Safe editing of catchment descriptors and flood data

Safe editing modes now protect the accidental overwriting of

catchment descriptors and flood data.

Integration with the HiFlows-UK website

The WINFAP-FEH 3™ software links to the HiFlows-UK website to

allow quick assessment gauging-station quality and relevance when

used in pooling or donor QMED adjustment.

Copy and paste functionality

WINFAP-FEH 3™ provides the ability to copy from integrated tables

and paste directly into reports for accurate audit trails of design

flood estimation.

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2 Appropriate use

The WINFAP-FEH 3™ software implements the FEH statistical methods

for flood estimation. This User guide is not intended to present the full

detail of these procedures and the User is referred to FEH, Volume 3 for

further details.

It is strongly recommended that WINFAP-FEH 3™ should be used by a

competent hydrologist who has received appropriate training. As stated in

the FEH, your use of the methods is undertaken at your own risk. Please

contact WHS for more information on training courses.


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3 Background

The FEH approach to estimating peak flow for a given return period

(T) involves three steps: first, estimating the index flood, the median

annual maximum flood (QMED); second, estimating an appropriate flood

growth curve (zT); and third, deriving a flood frequency curve which

relates the index flood to the growth curve to provide an estimate of the

peak flow for return interval (QT) according to:

These procedures can be applied to gauged catchments, where observed

data is available, as well as ungauged catchments via two methods:

Single Site Analysis is one based on an observed flood

series at the target catchment alone and cannot be applied to

ungauged catchments.

Pooled Analysis can be applied to an ungauged target catchment.

This method uses catchment characteristics to identify a number

of gauged catchments which are hydrologically similar to the

target catchment. The observed flood data for the ‘similar’ gauged

catchments are then used to estimate peak flows at the ungauged

target catchment. Pooled Analysis may supplement Single Site

Analysis to improve the robustness of the design flood estimation.

The choice of analysis depends not only on what type of data is available

(gauged or ungauged) but also the length of flood data record available

compared to the return period T to be estimated. The choice of analysis

method is outlined in Section 7.

The WINFAP-FEH 3™ software enables Users to perform both Single

Site Analysis and Pooled Analysis in accordance with FEH procedures.

The software is pre-loaded with flood peak data sets from over 900 UK

catchments. Additional flood peak data can be added to the software

archives by the User. Results can be readily exported from the software

and projects can be saved by the User, storing station details, analysis

methods etc which can be retrieved for future for further analysis.

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4 Outline

This User guide is arranged to describe the common tasks associated with

the use of the WINFAP-FEH 3™ software and to guide the User through

the process of obtaining peak flow estimates for floods of different

return periods, using different data sources. The guide is arranged in the

following sections:

Section 5 describes using the basic features of the WINFAP-FEH 3™

interface.

Section 6 details the construction of a WINFAP-FEH 3™ project,

required before any analysis can be undertaken. The information

stored in a Station File (*.cd3) is explained.

Section 7 details the FEH guidance for choosing the right analysis

method depending on the data available and return period required.

Section 8 describes the Single Site Analysis method for sites with

some observed AM data.

Section 9 describes the Pooled Analysis method for sites with little or

no observed flood peak data.

Section 10 shows a tabulation of all menu and sub-menu options.

Section 11 A detailed glossary.

Section 12 References and further reading.

4.1 Definitions and conventions

The conventions adopted throughout this document are explained below:

Convention Explanation

CAPITALS Keys on the computer keyboard are shown in capitals, for example the

escape key is shown as ESC.

[menu choice] Functions can be accessed via drop-down menus or clicking on the

appropriate icon/tab. Where menus are referenced, menu choices are

indicated by square brackets. For example, [File] [New Project].

Bold Indicates that this text will appear within the window currently displayed.

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5 Using the WINFAP-FEH 3™ software

5.1 Installation

5.1.1 How to install

Installation requires Administrative User Access Rights. The default paths

for installation require files to be written to the Program Files Directory,

which is protected for Users with the lowest level access rights.

During installation there is an option to install the software for the current

User or All Users. In general All users should be selected.

To install the WINFAP-FEH software from your CD, place the CD in the

drive of the target machine and run the ‘WINFAP-FEH setup.exe’ file. The

installation will prepare to install the software, displaying the window in

Figure 5.1 below.

Figure 5.1 Preparing to install window


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You should then see the window in Figure 5.2.

.

Figure 5.2 Installation welcome window

Click Next to continue. You should see the Licence Agreement window

in Figure 5.3 below.

.

Figure 5.3 Licence Agreement window

You must agree to the terms and conditions in the licence agreement

before you can install the software. Select the I accept… button and click

Next. After entering your customer information and clicking Next, you


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should see the Destination Folder window in Figure 5.4 below

.

Figure 5.4 Destination Folder window

The recommended location for the files to be installed is set by default. To

change from this default location click the Change… button and select a

new folder. Click Next to proceed. You should see the installation Setup

Type window in Figure 5.5 below.

.

Figure 5.5 Installation Setup Type window

This window allows you to select the features to install.


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It is recommended that you select Typical when installing

WINFAP-FEH 3™, or the software may not function correctly.

Click Next to proceed to Ready to install… Figure 5.6.

Figure 5.6 Ready to begin installation message in the InstallShield Wizard window

Click Install to begin the installation. You should see the installation

progress bar in the Installing WINFAP-FEH window in Figure 5.7 below.

Figure 5.7 Install progress window


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When the installation is complete you should see the message below in

the InstallShield Wizard Completed window in Figure 5.8 below.

Click Finish.

Figure 5.8 Installation completed window

5.1.2 Licence management

WINFAP-FEH 3™ is protected by a licence held on a USB ‘dongle’.

This allows the software to be used on different PCs non-concurrently.

The USB stick holding the licence information is supplied with the

software, and must be inserted into the computer whenever the

software is to be run.

In order to use the dongle licence the User must browse to the file

WINFAP-FEH.lic on the USB dongle at the Login window, by clicking the

Browse button. During subsequent uses the software will automatically

look for the licence in the same place, however if the drive letter of the

USB stick has changed (for example if another device is being used) you

may need to browse for the file again.

If the licence file is valid you will see a message on the Login window

that you have a valid licence for the software.


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5.2 Login window

Once the User has activated the software licence following the software

installation instructions, the Login window is presented, see Figure 5.9.

The software is run by selecting the Accept button. By selecting this

button the User confirms that they have read and accepted the licence

terms and conditions presented within this window.

Figure 5.9 Login window

Following the Login window the Welcome window is presented and

the User can select whether to open a new project, return to an existing

project or select an existing project from a list of most recent projects, see

Figure 5.10.

Figure 5.10 Welcome window with a selection of types of project to open


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5.3 Main window

Once an existing project or blank project has been selected, the main

window appears, see Figure 5.11.

Two tabs appear in the left-hand panel, Sites and Pooling-group, which

contain details of catchments which are being assessed for Single Site

Analysis or Pooled Analysis, respectively.

Figure 5.11 Main window

The data is stored within the software in several forms:

A Station File contains information relating to the observed flood

frequency records for a gauging station. For each gauging station

there are generally three files, *.cd3, *.AM and *.PT. Station files

exist for all gauged sites for which reasonable quality flood data is

available, as defined through an Environment Agency project called

HiFlows-UK, and approximately 960 station files are pre-loaded in the

WINFAP-FEH 3™ software. This data supersedes the data provided with

the FEH and provides the User with additional information about data

quality and applicability for use in QMED estimation and with pooling

groups. It is noted that all station files (including the pre-loaded files)

are able to be edited by the User.

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A project is saved by the User as an *.feh which contains a list of

loaded Stations with details of any pooling groups and User-adjusted

settings. This enables a User to open an existing project and continue

working with previously saved data.

The main menus and icons available on the main window are shown

below on Table 5.1. A full description of all menus and sub-menus is

contained in Section 10.

Menu / Icon Description

Opens new project

If no project is currently open – this icon opens an existing project. If a

project is open – this icon will allow User to add a new Station File to the

Sites tab.

Saves the current project or the selected Station File

[File] Management of projects and Station Files; printing functionality; exiting

from the software.

[Options] Setting of default modelling parameters applied in the software; setting of

default display parameters; selection of the location of the Station Files.

[Single Site] Single Site analysis methods including the Station details and Summary

Info windows; setting distributions, standardisation methods and

confidence intervals; viewing results of Single Site Analysis.

[Pooled Analysis] Pooled Analysis methods including the Pooling-group details window;

exploratory data analysis, distribution selection and final development of

flood frequency curves; viewing of results of Pooled Analysis.

[View] Options for tool bar, status bar and project pane.

[Window] Options for arranging layout of windows.

[Help] Access to Help PDF and About … details.

Table 5.1 Main menus and icons available from the main window

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5.4 General tips

Exporting tabulated data from the software is achieved by L-clicking

on the top right hand corner of a table to select the entire table.

CTRL-C copies the selection to the clipboard and CTRL-V can be used

to paste the data into a spreadsheet or word-processor document.

Exporting graphs can be achieved by firstly L-clicking on the graph to

select it, then CTRL-C copies the selected graph to the clipboard and

CTRL-V can be used to paste the data into a spreadsheet or word-

processor document.

6 Creating a project

To begin the flood estimation procedure the User must first create a

project. A project consists of one or more Station Files that have been

used for either Single Site Analysis or Pooled Analysis or both. It also

contains the results of analysis undertaken.

The User should select [File] [New Project] which will open the left-hand

panel with Sites and Pooling-group tabs.

Next an existing Station File is added via the [File] [Open Station] menu

which enables the User to browse in an existing Station File (*.cd3).

Alternatively a new Station File may be created via the [File] [New Station

/ Ungauged site] menu choices (described in the next section). The

stations will appear on the Sites tab.

Additional stations can be added to the project for Single Site Analysis.

The results of any Pooled Analysis (appearing on the Pooling-group tab)

are automatically associated with the current project and details of the

pooling group(s) will be saved on the project.

Once a station has been added to the Sites tab the User can review

and edit the data stored for the station via the Station details window,

accessed from [Single Site] [Station details].

6.1 Station details window

The data held for a given station can be viewed on the Station details

window which is accessed by double L-clicking on the station on the

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Sites tab or via the [Single Site] [Station details], see Figure 6.1. If the

station is a new station added by the User this form will be blank,

awaiting the User to enter details.

Figure 6.1 Station details window showing data for existing station

Within the Station details window the following can be accessed

by the User:

Contextual information regarding the flow measuring device,

catchment and suitability of the record for use in the flood estimation

are shown on the STATION, CATCHMENT, QMED Suitability and

Pooling Suitability tabs. The User can add comments on the User tab.

The Annual Maxima tab shows the time series of annual maximum

(AM) flow values recorded and summary information regarding the

AM record.

The Peaks Over Threshold tab shows the time series of peaks over

threshold (POT) flow data and summary information regarding the

AM record.

The Catchment descriptors tab shows the catchment descriptors for

the catchment as derived from the FEH CD-ROM 3.

Edits to data held for a station can be made via the Station details window.

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The Edit details button enables the User to edit the contextual

information fields.

On the Annual Maxima tab the Edit AM button enables the User to

edit the AM series, add new AM data and delete AM data.

On the Peaks Over Threshold tab the Edit POT button enables the

User to edit the AM series, add new AM data and delete AM data.

Edits can be made on the Catchment descriptors tab by use of

individual edit buttons

The User may also create a new Station File using data exported from the

FEH CD-ROM 3. This process is detailed below:

Open the FEH CD-ROM 3 software.

Select your target catchment by left-clicking on the map or using the

grid reference input boxes.

View the catchment pressing the Query button.

In the resultant Catchment descriptors dialogue box, press

the Export button. For the exported file to be compatible with

WINFAP-FEH 3™, the *.cd3 file format must be selected.

Save the *.cd3 file in a suitable location and import into

WINFAP-FEH 3™ using the [Open Station] as described on page 24.

Once the User has reviewed the information stored against a station,

the flood estimation procedures can begin. Two estimation procedures

are available: Single Site Analysis and Pooled Analysis. The choice of

procedure is discussed in the following section.

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7 Choice of analysis method

The WINFAP-FEH 3™ software enables two types of flood frequency

analysis to be undertaken:

Single Site Analysis is one based on an observed flood series at

the target catchment alone and cannot be applied to ungauged

catchments.

Pooled Analysis can be applied to an ungauged target catchment.

This method uses catchment characteristics to identify a number

of gauged catchments which are hydrologically similar to the

target catchment. The observed flood data for the ‘similar’ gauged

catchments are then used to estimate peak flows at the ungauged

target catchment. Pooled Analysis may also supplement Single

Site Analysis, through the Enhanced Single Site Analysis; this is

recommended where there is limited data at the subject site, but the

record is not long enough to allow robust Single Site analysis.

The choice of analysis depends not only on what type of data is available

(gauged or ungauged) but also the length of flood data record available

(NUMYRS) compared to the return period (T) to be estimated, as follows:

Length of record

(years)

Single site analysis Pooled analysis Description

NUMYRS < 0 No Yes Pooled analysis

0< NUMYRS < 2T No Yes Enhanced single site analysis

≥ 2T years Yes For confirmation* Single site analysis prevails

* Subject site excluded from pooling group

The FEH recommendation is therefore that Single Site Analysis alone is

insufficient unless the site record is more than twice the target return

period. Pooled Analysis is essential for flood estimation if the catchment is

ungauged or has only a short record. Pooled Analysis is recommended if

the record length is less than twice the target return period.

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8 Single Site Analysis

The first type of analysis in WINFAP-FEH 3™ is the Single Site Analysis.

Single Site Analysis is based on an observed flood series of Annual

Maxima (AM) or Peaks Over Threshold (POT) data at the target

catchment alone and cannot be applied to ungauged catchments.

The three steps in the process are as follows:

1 Estimate the index flood QMED

2 Construct a flood growth curve

3 Derive flood frequency curve as the product of QMED and flood

growth curve.

8.1 Estimating QMED

QMED can be derived from a gauged flood flow record, either Peaks Over

Threshold (POT) or Annual Maximum (AM) series, depending on record

length. The FEH provides the following guidelines for estimation

of QMED using gauged data:

>13 years: median of the ranked AM flood series

2 to 13 years: from POT data

< 2 years: extend the subject site Annual Maximum or POT record

by correlation with a nearby long record site – or treat as an

ungauged site and use the approaches detailed in Section 9.1.2.

The software calculates estimates of QMED based on the above

criteria and FEH guidance (FEH, Volume 3) using the data stored in

the Station File.

The User selects the station from the Sites tab on the left hand pane

and then chooses [Single Site] [Summary info] to display the Single Site

summary information window on which the AM and POT tabs display

the QMED values calculated using these two types of data, see Figure 8.1.

The QMED tab on this window shows the QMED value obtained using

catchment descriptors (QMEDcds) (see Section 9.1.2) and the optimal

QMED value from flood peak data (QMEDobs).

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Figure 8.1 Single Site summary information window

8.1.1 Estimating QMED in gauged urbanised catchments

Flood frequency behaviour is known to be affected by the level of

urbanisation within a catchment. However, when QMED is estimated

from observed AM or POT data the effects of urbanisation on QMED are

included within that data, and so no adjustments need be made.

8.2 Constructing a flood growth curve

A flood growth curve is constructed by fitting a distribution to the

observed AM data. In most situations the Generalised Logistic (GL)

distribution is recommended for UK flood data. Estimation of the growth

curve parameters is achieved using the L-moment method.

The User can choose from a list of pre-defined distributions via the [Single

Site] [Select distributions] menus and options presented on the Select

distributions window. Multiple distributions can be chosen to enable the

User to compare the fit of the data to the different curves.

Alternatively, [Single Site] [User-defined distributions] enables the User to

define additional distributions.


30

The [Single Site] [Confidence Intervals] selection enables the User to

define how confidence intervals relating to the fit of the distribution

are derived.

Once the distribution and standardisation variable have been chosen

the [Single Site] [Station Fittings] and [Individual Distribution Fits] (if

multiple distributions have been chosen) windows can be used to

examine the parameters derived from the observed data, see Figure 8.2.

Figure 8.2 Individual Distribution Fits window

The Individual Distribution Fits window also includes:

A Calculate confidence intervals button which calculates

confidence intervals for the fitted distribution. The size of the

confidence intervals is set via the [Options] [Project Options] and

Confidence Intervals tab. This tab also enables the User to select to

show confidence intervals on plots.

A Calculate RP from magnitude button enables the User to

interpolate on the growth curve to predict peak flows from return

intervals and vice versa.

The [Single site] [Graphs] [Frequency Curve] selections can be used

to view the flood growth curves generated for the User selected

distribution(s), see Figure 8.3. The User can then select the most

appropriate distribution to adopt for the catchment. Note that the FEH

recommends the Generalised Logistic distribution and the L-moment

fitting method for UK flood data. Other distributions and methods can

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31

be used, but only an experienced hydrologist, with evidence for an

alternative distribution and knowledge of alternative methods should

proceed with a different approach.

Figure 8.3 Multiple flood growth curves fitted to observed data

8.3 Obtaining the flood frequency curve

The flood frequency curve is obtained by multiplying the growth curve

by QMED. This enables any flood QT of return period T years to be

estimated:

Within the software this is readily achieved by changing the choice of

standardisation variable via the [Single Site] [Standardise] menus and

choosing the ‘Not standardised’ option. This causes the plots and

tabulations of data produced to relate to a flood frequency curve

(Figure 8.4) rather than a flood growth curve (as shown in Figure 8.5)

which is shown if a standardisation variable is chosen.


32

Figure 8.4 Flood frequency curve for 4005 achieved by choosing ‘Not standardised’ under the

[Single Site] [Standardise] menu options. The y-axis has the dimensions of flow units.

Figure 8.5 Flood growth curve for 4005 standardised by the median (QMED).

The y-axis is dimensionless in this plot.


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9 Pooled Analysis

In FEH, hydrological similarity is judged with regards to the catchment

descriptors: catchment area (AREA), standard average annual rainfall

(SAAR), flood attenuation by reservoirs and lakes (FARL) and floodplain

extent (FPEXT). The observed flood data for the ‘similar’ gauged

catchments are then used to estimate peak flows at the ungauged target

catchment. The basic steps in the process are:

1 Estimate the index flood QMED

2 Define a pooling group for the catchment of interest

3 Construct a flood growth curve using the pooling-group data

4 Derive flood frequency curve as the product of QMED and flood

growth curve.

9.1 Estimating QMED

For pooled analysis the WINFAP-FEH 3™ software can estimate QMED in

several different ways. These values are presented to the User in the final

stages of the flood frequency curve estimation, following the [Pooled

Analysis] [Flood frequency curve development] menu choices, see Section

9.4. At this point the User chooses which value of QMED should be used

to derive the flood growth curve. The derivations of the various values of

QMED are discussed in the following sections.

9.1.1 Calculating QMED from observed data

If AM or POT data are available, these can be used to estimated

QMED via the software in the same way as for Single Site Analysis,

see Section 8.1.

9.1.2 Estimating QMED from catchment descriptors

If the catchment is ungauged or has only a very short record of AM

or POT data (less than two years) the catchment descriptor method is

recommended for estimation of QMED. The method involves the use of

an equation established for essentially ‘rural’ catchments which derives

QMED from catchment descriptors: catchment area (AREA), standard

average annual rainfall (SAAR), hydrological soil properties (BFIHOST) and


34

upstream reservoirs and lakes (FARL). The equation used was updated by

Kjeldsen et al. (2008), and is given as:

Note that the catchment descriptor equation is a generalised model

applicable across the whole UK. Estimating QMED using two years’

flood data generally provides a better estimate than the catchment

descriptor method.

An estimate of QMED can be obtained from the software, using

the above equations, for any site loaded in the software, for which a

valid *.cd3 exists. The estimate of QMED can be viewed by selecting

the catchment in question from the Sites tab, then choosing

[Single Site] [Summary info] and the QMED tab to display the

estimate, shown as (QMEDcds).

9.1.3 Estimating QMED by data transfer

An estimate of QMED made using the catchment descriptor method can

be adjusted by using the Data Transfer method. This method involves

transposing flood peak information from a nearby ‘donor’ catchment.

Recent studies undertaken by Kjeldsen (2009) have confirmed geographic

proximity to be the dominant factor for selection of suitable donor

catchments.

The basic transfer process is as follows:

1 Select a gauged donor site, derive QMED at that site (QMEDg,obs).

The FEH provides the following guidance through ‘rules of thumb’

when comparing the subject catchment and a potential donor:

Primarily that consideration should be made as to the quality of the

flood data being transferred (ensure that the observed flood peak

record for the donor is of good quality). The HiFlows-UK website

provides further information about gauging station quality

AREA should not differ by more than a factor of 5

Soil and wetness indices (eg SAAR) should differ by no more

than 1.1

•

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35

If FARL < 0.95, exercise extreme caution

For urbanised catchments additional procedures will apply, and

reference should be made to the FEH.

2 Calculate an estimate of QMED from catchment descriptors at

both the subject site and donor site, QMEDs,cds and QMEDg,cds,

respectively.

3 Express the adjusted value of QMED for the subject site (QMEDs,adj)

by the following transfer equation:

where dsg is the geographical distance (km) between the centroids

of the catchments of the subject site and the donor site.

The WINFAP-FEH 3™ software enables the data transfer method to be

applied to estimate QMED in the following manner:

1 The choice of which QMED value is to be adopted is presented to

the User at the final stage of the process [Pooled Analysis] [Flood

frequency curve development] see Section 9.4.

The User can choose to use a donor catchment to estimate QMED

via the software by following the [Pooled Analysis] [Flood frequency

curve development] menu selections on the Estimate QMED window

and selecting Donor station as the method. A list of possible donor

catchments are then provided, ranked in order of geographical

proximity to the subject catchment. Judgement is required when

choosing an appropriate donor catchment, and the most appropriate

catchment descriptors, and a button linking to the Hiflows-UK

website, are provided in the list to assist this.

2 The software then applies the above transfer equation using the

donor selected by the User, to derive a QMED estimate. The estimate

is displayed to the User in the box adjacent to the Donor station

heading and will be carried forward to rescale the flood growth curve.

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36

9.1.4 Estimating QMED in ungauged urbanised catchments

Flood frequency behaviour is known to be affected by the level of

urbanisation within a catchment. The fraction of the catchment

considered to be urbanised is described by the catchment descriptor

URBEXT2000. For ungauged catchments, where QMED is estimated

using catchment descriptors (Section 9.1.2), and URBEXT2000 > 0.03

it is necessary to adjust the initial ‘rural’ QMED value (QMEDrural) for

urbanisation as follows:

The Urban Adjustment Factor (UAF) is calculated automatically by

WINFAP-FEH 3™ (a function of URBEXT2000 and SPRHOST) and applied to

QMEDrural to give the final QMED value for the subject site, if the User

chooses to apply an urban adjustment.

The User confirms this adjustment at the final stages of developing the

flood frequency curve via the [Pooled Analysis] [Flood frequency curve

development] selection, as described in Section 9.4.

Note: When a catchment is urbanised (ie URBEXT2000 > 0.03) the use of

Data Transfer methods (Section 9.1.3) to improve the estimate of QMED

is not recommended.

9.2 Defining a pooling group

A pooling group contains sites that are hydrologically similar to the

subject site, and is formed by choosing catchments with similar AREA,

SAAR, FARL and FPEXT. Therefore, the catchments in a pooling group can

be hydrologically similar, but geographically dispersed. The observed AM

flood peak data for the catchments in the pooling group are then used to

construct a flood growth curve for the subject site.

Choosing the [Pooled Analysis] [Create pooling group] option in the

software will initiate the definition of a default pooling group for the

subject catchment (selected on the Sites tab) from the WINFAP-FEH 3™

Station File records for catchments that satisfy the following criteria:


37

There are at least 5 years (preferably 8) of AM data

Catchment descriptors (AREA, SAAR, FARL, FPEXT) are known

The catchment is essentially rural (URBEXT2000 < 0.030)

Catchment area ≥ 0.5 km2.

Options on the Pooling-group development window enable the User

to specify additional criteria used to construct the pooling group.

Figure 9.1 Pooling-group development window

The default pooling-group size is 500 years of AM data. This means that

gauges will be added to the pooling group until the sum of all AM record

lengths reaches 500. The Define custom pooling-group size option

on this window enables this value to be changed. This has been updated

(Kjeldsen et al. 2008) from the FEH recommending that the combined

record length is five times the target return period required.

The treatment of the Subject Site as Ungauged or Gauged (Enhanced

single site) can be chosen from the radio buttons. If the latter is adopted

then the subject site itself will be included in the initial pooling group, but

with a greater weighting reflecting the importance of at-site data. The

Gauged (Enhanced single site) option will not be available for urban

sites, or sites with no flood peak data.

The details of the pooling group for the subject catchment are presented

to the User on the Pooling-group details window, see Figure 9.2.

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•

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Figure 9.2 Pooling-group details window

9.2.1 Pooling-group details window

The Stations selected for the Pooling-group are listed on the

Pooling-group details window under the following tabs:

AM Data tab

Distance – this is the Euclidean distance between the subject

catchment and the pooling-group catchment calculated using the

variable AREA, SAAR, FARL, FPEXT. Hence, smaller values indicate

catchments that are most hydrologically similar to the subject

catchment.

Record length – the number of years of AM values in the record.

QMEDobs – the observed QMED value calculated from the AM data.

L-CV, L-SKEW – sample L-moments of AM series.

Discordancy – this is a measure of how different the AM data is from

the pooled values L-moment ratios; a higher value indicates a ‘more

different’ dataset.

The AM Graphs button on this form displays plots of location;

seasonality of flood peaks; L-moment graphs and individual flood growth

curves for each member of the current pooling group.

Catchment Descriptors tab

Distance – as described above.

AREA – catchment area.

SAAR – standard annual average rainfall, a measure of catchment

wetness.

FPEXT – an index of floodplain coverage within the catchment.

•

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•

•

•

•

•

•

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39

FARL – an index for assessing the relative important of flood

attenuation due to reservoirs and lakes.

URBEXT2000 – a measure of urbanisation within the catchment.

The HiFlows-UK button brings up a link to the relevant HiFlows-UK page

in order that the user can further assess suitability for inclusion in the

pooling group.

The membership to the pooling group can be modified by removing

existing catchments or adding new catchments to the group using the

Add Site and Remove Site buttons on this window. This is discussed

further in the following section.

9.2.2 Reviewing and adapting pooling groups

The User is encouraged to review the pooling group to ensure that the

best stations are selected to predict a flood growth curve for the subject

site. Consideration should be given to:

Quality of the flood peak data for catchments in the

pooling group. A colour coding system has been adopted to assist in

the identification of:

1 Catchments with short records (default GREY)

2 Catchments deemed by the HiFlows-UK project to be not suitable for

use in a pooling group (default YELLOW)

3 Catchments deemed by the HiFlows-UK project to be not suitable for

use in a pooling group or to estimate QMED (default MAGNETA)

4 Catchments with a significant discordancy measure (default RED)

The heterogeneity of the pooling group. Ideally, all catchments

in a pooling group would be similar to each other and to the subject

catchment. The degree of similarity of each pooling group member to

the pooling group as a whole can be assessed using the Heterogeneity

statistic (H2). This compares the variability of L-CV and L-skewness

across the pooling group. A high H2 value indicates that group

members may have different growth curves. The H2 statistic for a

pooling group can be examined via the [Pooled Analysis] [Exploratory

data analysis] [Heterogeneity measure] menu choices.

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•

•

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40

Note: both the discordancy and heterogeneity measures are intended

to assist the User in making choices about pooling group membership.

They should not be used in isolation to refine pooling groups, expert

judgement is essential. For more background to the diagnostic tools, see

FEH Volume 3, Chapter 16.

A further method for evaluating the heterogeneity of the pooling group

can be accessed via the [Pooled Analysis] [Exploratory data analysis]

[Goodness Of Fit test] menu choices. This presents the User with the

Goodness-Of-Fit details window. The goodness-of-fit (GOF) for a

particular distribution is judged by comparing the L-kurtosis for the fitted

distribution to the (bias corrected) L-kurtosis of a kappa distribution

fitted to the pooled L-moments. The distance between these two values

will then be standardised by the standard deviation of the L-kurtosis

for the kappa distribution; giving the goodness-of-fit measure Z. The

goodness-of-fit measure is used to decide whether a distribution gives

an acceptable fit and to find the best-fitting distribution. The fit will be

judged to be acceptable if |Z| =< 1.64. The best-fitting distribution is the

one with the lowest absolute goodness-of-fit value (= closest to zero).

Figure 9.3 The Goodness Of Fit window

The Generalised Logistic distribution gives the best overall fit to the UK

data. The next most useful is the Generalised Extreme Value distribution.


41

9.3 Constructing a flood growth curve

Once the User has identified an appropriate pooling group for a given

subject catchment, the WINFAP-FEH 3™ software can be used to perform

the necessary calculations to estimate the flood growth curve for the

subject catchment.

This requires that the User select a distribution for the flood growth

curve. Using the software, this is achieved via the [Pooled Analysis] [Select

distributions] or [Pooled Analysis] [User defined distributions] menus. The

former selection gives the User a choice from eight possible distributions

(note that multiple distributions can be selected). The latter selection

enables the User to define alternative distributions.

For a given distribution, a growth curve for the subject site is calculated as

a weighted average of the single-site growth curves for the catchments

in the pooling group. The weightings are a function of the record length

and similarity to the subject site, see Kjeldsen et al. (2008).

The flood growth curve can be viewed by selecting [Pooled Analysis]

[Graphs] [Growth curves] from the menu, an example of which is shown

in Figure 9.4.

Figure 9.4 Flood growth curve


42

9.4 Obtaining the flood frequency curve

Once a flood growth curve has been constructed using a pooling group,

the final steps to producing a flood frequency curve are made using the

WINFAP-FEH 3™ software as follows:

1 The [Pooled Analysis] [Flood frequency curve development] menu

initiates a series of windows which the User progresses through to

complete the computation of the flood frequency curve:

Adjust URBEXT2000 window – enables the User to adjust for

urbanisation. Several methods of doing this are available:

– Existing URBEXT2000 value

– Use the national average model for urban growth, according to

the year as chosen by the User in the input box (URBEXT2000 is

adjusted according to this model automatically)

– A User-supplied value of URBEXT2000

– A User-specific value of Urban50k, which is automatically used

to estimate URBEXT2000.

Estimate QMED window – enables the User to choose or supply a

value for QMED to be used to eventually rescale the flood growth

curve to a flood frequency curve. Options include:

– Using AM data

– Using POT data

– Using catchment descriptors

– Entering a User-defined value

– Using donor station adjustment, as described in Section 9.1.3.

Construct Flood Frequency Curve window – enables the User to

choose whether to apply the Urban Adjustment Factor (UAF) to the

QMED value and the growth curve.

Once these windows have been completed, the flood frequency curve for

the subject site has been developed and can be accessed as follows:

2 The [Pooled Analysis] [Distributions] [Growth curve fittings] selection

can be used to view the distribution parameters for the pooled growth

curves for the subject site, see Figure 9.5.

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43

Figure 9.5 Growth curve fittings window

3 The [Pooled Analysis] [Distributions] [Fittings for FFC] selection can be

used to view the flood frequency curves for the various distributions,

see Figure 9.6. These are the flood growth curves rescaled by the

User-selected QMED value from Step 1.

Figure 9.6 Fittings for Flood Frequency Curve window

4 The [Pooled Analysis] [Graphs] [Growth curve] and [Pooled Analysis]

[Graphs] [Flood frequency curve] options enable the User to view the

growth and frequency curves derived from the pooling group, for the

subject site, see Figure 9.7


44

Figure 9.7 Growth and flood frequency curves displayed

Other graphs available at this point include:

[Pooled Analysis] [Graphs] [Catchment descriptors] – illustrates

the ‘location’ of the subject site in the data space of a variety of

catchment descriptor variables. The subject site is shown as a cross (X)

and the members of the pooling group as dots on a histogram.

[Pooled Analysis] [Graphs] [Station record parameters] – illustrates

distribution of the members of the pooling group with respect to

flood behaviour. Individual flood growth curves for each member of

the pooling group are illustrated.

[Pooled Analysis] [Graphs] [All analysis graphs] – illustrates all graphs

shown on the [Catchment descriptors] and [Station record parameters]

windows.

[Pooled Analysis] [Graphs] [3D L-moment graph] – shows a three-

dimensional plot of the L-CV, L-skewness and L-kurtosis for each of

the pooling group members and the subject site itself.

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10 Tabulation of menus and sub-menus

Menu Menu item Description

[File] Open project Opens an existing project.

Close project Closes current project.

New Station /

Ungauged site

Adds a new station or ungauged site to the

Sites tab, which then enables data to be entered

for the station.

Open Station Opens an existing Station File and adds to the

Sites tab.

Remove Selected Item Removes the selected station from the Sites tab or

selected pooling group from the Pooling-group tab.

Save Saves the current project or the selected Station File

Save as Saves the current project or the selected Station File

under a different name.

Save all Saves both the project and data files.

Print All Dialogs Enables the User to print all active dialogs/windows.

Print setup Enables the User to define the print device and

settings to be used.

… list of recent Projects Presents the User with a list of recent projects which

may be selected.

Exit Exits the software.

[Options] Return Periods Enables the User to choose the selection of return

periods adopted throughout the software.

Graph options Provides the User with options for changing the

appearance of graphs produced by the software.

Project Options Enables the User to modify default options which

will then be saved to the Project.

General options Load options tab enables the User to browse in

the location of the Station Files. Donor options tab

enables the User to specify the number of donor

Stations to be used to estimate QMED by Data

transfer, see Section 9.1.3.

Error Log View details of any errors.


46

Menu Menu item Description

[Single site] Station details Opens the Station Details window for the currently

select station.

Summary info Provides summary information for the currently

selected station of: annual maxima, peaks over

threshold and median flood flow.

Select distributions Enables the User to select from pre-defined

distribution/s to be used to fit to observed AM data.

User distributions Enables the User to define a new distribution to be

used to fit to observed AM data.

Standardise Enables the standardisation variable to be selected.

Confidence Intervals Enables the User to set confidence intervals

for calculation.

Station Fittings Tabulates the fitted parameters for Flood growth

curves produced by the selected distributions. Also

includes a tabulation of points on fitted curves.

Individual

Distribution Fits

Provides distribution parameters and tabulation of

points on fitted curves for an individual distribution.

Graphs [Time series curve] illustrates the time-series of AM

and POT data.

[Frequency curve] illustrates the growth curves fitted

to the selected distributions.

[Pooled

Analysis]

Create pooling group Initiates the identification of the default pooling

group for the selected subject site.

Pooling group details Illustrates details of the current pooling group.

Exploratory data

analysis

Enables the heterogeneity and goodness of fit for

the current pooling group to be examined.

Select distributions Enables the User to select from pre-defined

distribution/s to be used to fit to observed AM data.

User defined

distributions

Enables the User to define a new distribution to be

used to fit to observed AM data.

Flood frequency curve

development

Initiates the final step in generating a flood

frequency curve, see Section 9.4.

Distributions [Growth curve fittings] provides the User with details

of the fits of the pooled growth curve to the chosen

distributions.

[Fittings for FFC] provides a tabulation of points on

the fitted curve/s for each distribution selected by

the User. Values in cumecs.


47

Graphs [Catchment descriptors] – illustrates the ‘location’

of the subject site in the data space of a variety of

catchment descriptor variables. The subject site is

show as a cross (X) and the members of the pool as

dots on a histogram.

[Station record parameters] illustrates distribution of

the members of the pooling group with respect to

flood behaviour. Individual flood growth curves for

each member of the pooling group are illustrated.

[All analysis graphs] illustrates all graphs shown on

the [Catchment descriptors] and [Station record

parameters] windows.

[3D L-moment graphs] shows a three dimensional

plot of the L-CV, L-skewness and L-kurtosis for

each of the pooling group members and the subject

site itself.

[Growth curves] shows the fitted parameters for the

pooled growth curves for the subject, for each of the

chosen distributions.

[Flood frequency curve] tabulates the final Flood

Frequency Curve points for the chosen distributions

(in cumecs).

[View] Tool Bar Toggles the tool bar of icons on and off.

Status Bar Toggles the status bar at the bottom of the Main

window on and off.

Project Toggles the Project details (Sites and Pooling-group

tabs panel) on and off.

[Window] Cascade Arranges windows currently displayed.

Tile Arranges windows currently displayed.

Arrange icons Arranges minimised windows.

… list of windows List windows currently available.

[Help] Open Help PDF Opens the current Help File PDF document for the

software.

About WINFAP-FEH Provides version information etc regarding software.


48

11 Glossary

Annual Maximum (AM) series Consists of the largest observed flow in

each water year. It is straightforward to obtain and to analyse and is the

most commonly available form of flood data. AM data do not indicate

whether several major floods occurred in a water year; only the single

largest flow is recorded.

The Base Flow Index (BFI) Can be conceptualised as the proportion

of the long-term river flow considered to be derived from groundwater

stores, hence varies between 0 and 1. When considering an observed

flow record, the BFI is calculated as the ratio of the area under the

base flow hydrograph to the area under the flow hydrograph. In the

UK, permeable catchments (eg chalk) have higher values of BFI than

impermeable catchments (eg clay), see below.

Figure 11.1 Base flow hydrographs from chalk (left) and clay (right) catchments showing that the

BFI for chalk is higher than the BFI for clay

BFIHOST Baseflow index, as derived from HOST soil data. An estimate

of the Base Flow Index (BFI) of the catchment derived from the HOST soil

data. The BFI is calculated as the fraction of the total hydrograph that is

derived from baseflows. BFIHOST approaches unity in highly permeable

systems and approaches zero in very impermeable systems.

Flood Frequency Curve Defines a relationship between the size of

a flood (the peak flow in m3/s) and the return period, or expected

frequency of occurrence. Figure 11.2 shows a generalised flood

frequency curve.


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Figure 11.2 Generalised flood frequency curve

Flood Growth Curve (zT) A scaled (dimensionless) version of the

flood frequency curve. In the FEH methodology, a growth curve is

scaled by the index flood, QMED, so that it has a value of unity for

the two-year return period.

HiFlows-UK A database of flood peak data from UK gauging stations

that is maintained by the Environment Agency of England and Wales.

(http://www.environment-agency.gov.uk/hiflowsuk). This data set

underpins the FEH statistical methods and has been deployed as Station

Files within the WINFAP-FEH 3™ software.

Hydrology of Soil Types (HOST) A soil classification system developed

by Boorman et al. (1995) which maps the soil types of the UK into 29

classes based on their hydrological response.

Index Flood Represents the typical magnitude of a flood expected at a

given site every second year – in FEH this is by default the median annual

maximum flood or QMED.

Median annual maximum flood (QMED) The peak flow of the flood

which has a return period of two years.

Peaks Over Threshold (POT) series Consists of all distinct peak flows

that are greater than a selected threshold flow. Two POT series are

used in the FEH for flood frequency analysis: the POT1 and POT3 series

containing respectively an average of one and three events per year.


50

The POT1 series is alternatively known as the annual exceedance series.

The POT series is irregular; in some years there may be many floods, in

other years there will be no floods. POT data provide a more complete

picture of the flood regime than annual maxima but are also more

difficult to abstract and are not always available.

Return Period (T) The return period for a flood peak of Q m3/s is the

inverse of the probability that a peak flow of Q m3/s will occur in any

given year. That is, a flood peak with a return period of 20 years has a

probability of 0.05 of occurring in any given year.

Standard Percentage Runoff (SPRHOST) As derived from HOST soil

data. Reflects the percentage of rainfall that translates directly into

runoff. SPRHOST values approach unity in very impermeable systems and

approach zero in very permeable systems.


51

12 References and further reading

Boorman, D.B., Hollis, J.M. and Lilly, A. 1995. Hydrology of soil types: a

hydrologically-based classification of the soils of the United Kingdom. Report 126.

Institute of Hydrology. Wallingford.

Institute of Hydrology, 1999. Flood Estimation Handbook (five volumes), Centre

for Ecology & Hydrology, Wallingford, UK.

Bayliss, A.C., Black, K.B., Fava-Verde, A. and Kjeldsen, T. R., 2006. URBEXT2000

– a new FEH catchment descriptor. R&D Technical Report FD1919/TR, Department of

Food, Agriculture and Rural Affairs (DEFRA), London.

Bayliss, A. C. and Reed, D.W., 2001. The use of historical data in flood frequency

estimation. Report to Ministry of Agriculture, Fisheries and Food (MAFF), Centre for

Ecology and Hydrology, Wallingford, UK. Available at http://www.nwl.ac.uk/ih/feh/

historical_floods_report.pdf

Environment Agency, 2008. Improving the FEH Statistical Index Flood method

and software, Science Report SC050050/SR, Available at http://www.defra.gov.

uk/environ/fcd/research/default.htm

Environment Agency, 2009. HiFlows-UK provides flood peak data and Station

information, at around 1000 river flow gauging stations throughout the UK, for use

with the statistical flood estimation methods set out in the FEH.

http://www.environment-agency.gov.uk/hiflows/91727.aspx

Kjeldsen, T.R., Jones, D.A., and Bayliss, A.C., 2008. Improving the FEH statistical

procedures for flood frequency estimation. Environment Agency, Bristol, pp137.

Kjeldsen, T.R., 2009. Modelling the impact of urbanisation on flood frequency

relationships in the UK. CEH Wallingford Internal report, also currently under peer

review for publication.

The National River Flow Archive (NRFA) is part of the Centre for Hydrology and

Ecology, Wallingford, Oxfordshire, OX10 8BB, UK. The Archive is responsible for the

acquisition, archiving and validation of hydrological data for the United Kingdom

and produce the Hydrometric Register and Statistics publication.

http://www.ceh.ac.uk/data/nrfa/

Significant developments have been made to the industry-standard flood

estimation software, WINFAP-FEH 3™, incorporating major scientific

advances to the Flood Estimation Handbook statistical methods, and

offers improved functionality and ease of use.

The new science incorporated within the software includes:

Enhanced single-site analysis for pooling at gauged sites

New catchment descriptors (FPEXT, CENTROID)

Improved estimation of QMED from catchment descriptors

New automated donor adjustment method for QMED

Enhanced pooling procedures (new similarity index)

New urban adjustment method

The software has been re-engineered to produce a significantly more

user-friendly interface and logical menu structure, including:

Licensing via USB ‘dongle’

Intuitive and user-friendly menus

Improved pooling group development and flood frequency

curve wizard

Full integration with FEH CD-ROM 3 using new CD3 files

Calculator tool for estimating return periods and peak flows

from analyses

Integration with the HiFlows-UK website

Safe editing of catchment descriptors and flood data

© Wallingford HydroSoutions Ltd and NERC (CEH) 2009. All rights reserved.

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