Moffat Flood Study
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Dumfries and Galloway Council Moffat Flood Study August 2018 Kaya Consulting Limited Phoenix House, Strathclyde Business Park, Bellshill, North Lanarkshire, ML4 3NJ, UK Tel: 01698 464190, Web: www.kayaconsulting.co.uk Copyright of this Report is vested in Kaya Consulting Limited and no part of it may be copied or reproduced by any means without prior written permission from Kaya Consulting Limited. If you have received this Report in error, please destroy all copies in your possession and control and notify Kaya Consulting Limited. The findings and recommendations of this Report are for the use of the Client named on the cover and relate to the project described in the Report. Unless otherwise agreed in writing by Kaya Consulting Limited, no other party may use, make use of or rely on the contents of the report. No liability is accepted by Kaya Consulting Limited for any use of this report, other than for the purposes for which it was originally prepared and provided. Opinions and information provided in the report are on the basis of Kaya Consulting Limited using due skill, care and diligence in the preparation of the same. No independent verification of any of the documents or information supplied to Kaya Consulting Limited has been made. Kaya Consulting Limited Phoenix House, Strathclyde Business Park, Bellshill, North Lanarkshire, ML4 3NJ, UK Tel: 01698 464190, Web: www.kayaconsulting.co.uk Document Information and History Project: Moffat Flood Study Client: Dumfries and Galloway Council Client Representative: Brian Templeton Kaya Consulting Job Number: KC1381 Filename: Moffat Flood Study Project Director: Y Kaya Author Natalie Robson This document has been issued and amended as follows: Version Date Description Created by: Verified by: Approved by: V1.0 05/06/2018 Draft Report N Robson Y Kaya V1.1 13/08/2018 2nd Draft Y Kaya M Stewart Y Kaya V1.2 31/08/2018 Final Y Kaya Y Kaya Kaya Consulting Limited Phoenix House, Strathclyde Business Park, Bellshill, North Lanarkshire, ML4 3NJ, UK Tel: 01698 464190, Web: www.kayaconsulting.co.uk Kaya Consulting Ltd Table of Contents Executive Summary .............................................................................................................................. 1 1 Introduction .................................................................................................................................... 3 1.1 Background ............................................................................................................................... 3 1.2 Past Studies .............................................................................................................................. 3 1.3 Aims and Objectives ................................................................................................................. 4 1.4 Extent of Study Area and Description....................................................................................... 5 2 Data Collection and Review .......................................................................................................... 7 2.1 LiDAR Data ............................................................................................................................... 7 2.2 Mapping .................................................................................................................................... 7 2.3 Ground Survey Data ................................................................................................................. 7 2.3.1 Cross Sectional Survey Including Structures .................................................................... 7 2.3.2 Top of Bank Survey ........................................................................................................... 8 2.4 CCTV Survey ............................................................................................................................ 8 2.5 Kaya Site Visits ......................................................................................................................... 8 2.6 Historical Flood Information ...................................................................................................... 8 2.7 Condition of Existing Banks and Flood Defences .................................................................. 14 3 Hydrological Analysis ................................................................................................................. 15 3.1 Design Flow Estimation .......................................................................................................... 15 3.1.1 River Annan ..................................................................................................................... 15 3.1.1.1 Available Data .......................................................................................................... 15 3.1.1.2 Qmed and Pooling Group Assessment ...................................................................... 19 3.1.2 Birnock Water, Crosslaw Burn and Frenchland Burn...................................................... 22 3.1.3 Small Catchments at Gallow Hill ..................................................................................... 24 3.2 Partitioning Flows within the Modelled Catchments ............................................................... 27 3.3 Flow Distribution for Modelling Scenarios .............................................................................. 27 3.4 Climate Change ...................................................................................................................... 30 4 Assessment of Fluvial Flooding Risk ........................................................................................ 31 4.1 Modelling Approach ................................................................................................................ 31 4.1.1 Schematisation ................................................................................................................ 31 4.2 Topographic Datasets............................................................................................................. 31 4.2.1 Survey ............................................................................................................................. 31 4.2.2 Digital Terrain Model (DTM) ............................................................................................ 32 4.2.2.1 Top of bank survey ................................................................................................... 32 4.2.2.2 Channel cross sections ............................................................................................ 32 4.3 2D Model Domains ................................................................................................................. 39 4.4 Linking of 1D and 2D Domains ............................................................................................... 40 4.5 Hydraulic Structures ............................................................................................................... 40 4.6 Model Boundaries ................................................................................................................... 43 4.6.1 Upstream Boundary Condition ........................................................................................ 43 4.6.1.1 Partitioning of flow within the model area ................................................................ 43 Moffat Flood Study i Kaya Consulting Ltd 4.6.2 Downstream Boundary Condition.................................................................................... 48 4.7 Key Model Parameters ........................................................................................................... 49 4.7.1 Roughness ...................................................................................................................... 49 4.8 Model Calibration .................................................................................................................... 50 4.9 Model Runs ............................................................................................................................. 50 4.10 Model Results – Base Case Condition ............................................................................... 50 4.10.1 Flooding Mechanisms ..................................................................................................... 51 4.10.1.1 River Annan ............................................................................................................. 51 4.10.1.2 Birnock Water ........................................................................................................... 51 4.10.1.3 Crosslaw Burn .......................................................................................................... 51 4.10.1.4 Frenchland Burn ....................................................................................................... 52 4.11 The December 2015 Event ................................................................................................. 54 4.12 Model Sensitivity Analysis ................................................................................................... 54 4.13 Summary of Fluvial Flooding Risk ...................................................................................... 54 5 Assessment of Pluvial Flooding Risk ........................................................................................ 56 5.1 Culvert Capacity Estimation ..................................................................................................