Dumfries and Galloway Council Newton Stewart Flood Study Revised Final Report 22 April 2015 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. 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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: Newton Stewart Flood Study Client: Dumfries and Galloway Council Client Representative: James McLeod Kaya Consulting Job Number: KC635 Filename: Newton Stewart Revised Final April15 Project Director: Yusuf Kaya Author Callum Anderson, Michael Stewart, Yusuf Kaya This document has been issued and amended as follows: Version Date Description Created by: Verified Approved by: by: V1.0 26.11.2013 Draft Report C Anderson M Stewart Y Kaya V1.1 14.02.2014 Final C Anderson M Stewart Y Kaya V1.2 22.04.2015 Revised Final C Anderson M Stewart Y Kaya V1.1: Minor edits to address clients comments V1.2: Figures 16 and 19 updated and Section 6.9 on channel maintenance added, together with some minor edits for clarification Kaya Consulting Limited Phoenix House, Strathclyde Business Park, Bellshill, North Lanarkshire, ML4 3NJ, UK Tel: 01698 464190, Web: www.kayaconsulting.co.uk Table of Contents Executive Summary ............................................................................................................................... 1 1 Introduction ..................................................................................................................................... 4 1.1 Background ............................................................................................................................... 4 1.2 Aims and Objectives ................................................................................................................. 4 1.3 Extent of Study Area and Description ....................................................................................... 6 1.4 Catchment Description .............................................................................................................. 6 2 Historical Flood Information .......................................................................................................... 8 2.1 Historical Flood Information Received from SEPA ................................................................... 8 2.2 Historical Flood Information Received from Dumfries and Galloway Council .......................... 8 2.3 Other Historical Flood Information ............................................................................................ 8 2.4 Overview of November 2012 Flood Event ................................................................................ 8 3 Data Collection and Review .........................................................................................................12 3.1 Data Received from Dumfries and Galloway Council ............................................................. 12 3.1.1 LiDAR Data ...................................................................................................................... 12 3.1.2 Other Mapping and GIS Data .......................................................................................... 12 3.1.3 Historical Flood Information ............................................................................................. 12 3.2 Data Received from SEPA ...................................................................................................... 13 3.2.1 Flood Maps ...................................................................................................................... 13 3.2.2 Historical Flooding ........................................................................................................... 13 3.2.3 Hydrometric Data ............................................................................................................. 13 3.2.4 Rainfall Data .................................................................................................................... 14 3.3 Ground Survey Data ............................................................................................................... 15 3.3.1 Cross Sectional Survey Including Structures .................................................................. 15 3.3.2 Top of Wall Survey .......................................................................................................... 15 3.3.3 Doorstep Threshold Survey ............................................................................................. 15 3.4 Kaya Site Visits ....................................................................................................................... 15 4 Hydrological Assessment ............................................................................................................17 4.1 Objective and Location of Flow Estimate ................................................................................ 17 4.2 Catchment Description ............................................................................................................ 17 4.3 River Flow Data ....................................................................................................................... 18 4.4 Design Flow Estimation .......................................................................................................... 21 4.4.1 Methodology .................................................................................................................... 21 4.4.2 FEH Single Site Analysis ................................................................................................. 21 4.4.3 FEH Enhanced Single Site .............................................................................................. 23 4.4.4 Penkiln Burn..................................................................................................................... 25 4.4.5 Return Period Assessment for November 2012 Event .................................................... 25 4.4.6 Impact of Climate Change ............................................................................................... 25 4.5 Design Hydrographs for Model Boundary Conditions ............................................................. 26 4.5.1 Derivation of Hydrograph Shape ..................................................................................... 26 4.5.2 Partitioning of Flows between River Cree and Penkiln Burn ........................................... 27 Newton Stewart Revised Final April15 i 4.6 Sea Level Assessment ........................................................................................................... 28 4.6.1 Derivation of Still Water Levels ........................................................................................ 28 4.6.2 Impact of Climate Change ............................................................................................... 28 4.7 Joint Probability of Extreme Flows and Sea Levels ................................................................ 30 5 Hydraulic Assessment ..................................................................................................................31 5.1 Modelling Approach ................................................................................................................ 31 5.1.1 Schematisation ................................................................................................................ 31 5.2 Topographic Datasets ............................................................................................................. 31 5.2.1 Survey .............................................................................................................................. 31 5.2.2 Digital Terrain Model (DTM) ............................................................................................ 33 5.3 Key Hydraulic Structures ........................................................................................................ 33 5.4 Model Boundaries ................................................................................................................... 35 5.4.1 Upstream Boundary Condition ......................................................................................... 35 5.4.2 Downstream Boundary Condition .................................................................................... 35