Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Eastern CFRAM Study HA09 Hydraulics Report Lower Liffey Model DOCUMENT CONTROL SHEET Client OPW Project Title Eastern CFRAM Study Document Title IBE0600Rp0027_HA09 Hydraulics Report Model Name Lower Liffey Rev. Status Author Checked By Approved By Office of Origin Issue Date D01 Draft M.Houston A. Sloan I. Bentley Belfast 12/02/2014 D02 Draft M.Houston A. Sloan S. Patterson Belfast 11/07/2014 D03 Draft A. Sloan S. Patterson G. Glasgow Belfast 13/01/2015 F01 Draft Final A. Sloan S. Patterson G. Glasgow Belfast 13/03/2015 F02 Draft Final A. Sloan S. Patterson G. Glasgow Belfast 13/08/2015 F03 Draft Final A. Sloan S. Patterson G. Glasgow Belfast 05/08/2016 IBE0600Rp00027 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Table of Reference Reports Report Issue Date Report Reference Relevant Section Eastern CFRAM Study Flood Risk December IBE0600Rp0001_Flood Risk 3.2.3 Review 2011 Review_F02 Eastern CFRAM Study Inception August 2012 IBE0600Rp0008_HA09 Inception Various Report UoM09 Report_F02 Eastern CFRAM Study Hydrology September IBE0600Rp0016_HA09_Hydrology 4.4 Report UoM09 2013 Report_F01 Eastern CFRAM Study HA09 Liffey November 2001s4884- SC2 Survey Report v1 Various Survey Contract Report 2012 IBE0600Rp00027 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL 4 HYDRAULIC MODEL DETAILS 4.7 LOWER LIFFEY MODEL 4.7.1 General Hydraulic Model Information (1) Introduction: On the basis of a review of historic flooding and the extent of flood risk determined during the PFRA, the Eastern CFRAM Flood Risk Review (IBE0600Rp0027_Flood Risk Review) highlighted the River Liffey in Dublin City AFA as a HPW, subject to both fluvial and coastal flood risk. The Lower Liffey model stretches from Islandbridge to Dublin Bay and represents the portion of the Lower Liffey in Dublin City which is significantly affected by tidal influence. The total contributing catchment of the Lower Liffey model from Pollaphuca dam to Dublin Bay is 1,020 km². The model and AFA immediately upstream of the Lower Liffey HPW is referred to as the Lucan to Chapelizod AFA. The downstream boundary of the Lucan to Chapelizod model was extracted from the Lower Liffey. A number of tributary catchments enter the Liffey within the model extents including the Camac, Poddle and Dodder Rivers. The Lower Liffey model receives its main freshwater inputs from the upstream Lucan model and these three tributaries. These tributaries have been studied as discrete HPWs under the Eastern CFRAM (in the case of the Camac and Poddle watercourses) and under the Dodder CFRAM Study. The Dodder is the largest of these rivers and represents a contributing catchment of 113 km², flowing into the Liffey at Ringsend. The Dodder CFRAM predated the Eastern CFRAM, therefore an appropriate downstream control for the Dodder hydraulic model was established based on the ICPSS study which has more recently been used to establish the downstream conditions for the Lower Liffey model. The Camac is the second largest tributary, representing a contributing catchment of 58 km² and flows into the Liffey via a large culvert at Heuston Station. The Poddle is the smallest of the three, representing a catchment of 12 km² and flows into the Liffey via a culvert at Wellington Quay. The Lower Liffey model was used to provide downstream controls for these two tributaries. In addition to the main river inputs, run-off from Dublin City through the storm drainage network, combined storm overflows, other minor watercourses and direct from surface run-off, is estimated to account for up to 21 km² of urban catchment in total. The flow from this additional area is added to the model as a lateral inflow along the length of the Liffey main channel. There are two water level gauging stations within this modelled reach of the Liffey, however both are tidally influenced and are not suitable for flow measurements. There is one river gauging station (09022) IBE0600Rp00027 4.7.1 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL upstream of the model extents at the Leixlip hydro-electric power generation station, owned and operated by ESB. This station was not given a classification under FSU and is not a standard water level recorder station as operated by the OPW and the EPA. The flow data received have been derived from continuous recordings of flows and water levels through the various structures of the plant and converted into combined flow rates on request to ESB. The continuous flow records can be considered to have a high degree of confidence since they are derived from a combination of measured flows and fully defined water level - flow relationships (through the turbines, sluices and spillways) rather than based on an extrapolated relationship between water level and flow as is common at conventional gauging stations. However continuous recordings are only available for seven years from 2005 to 2011 inclusive and as such the Qmed derived from the AMAX series of 61.64 m³/s can be considered to have a low degree of statistical confidence. To ensure consistency with modelling throughout the greater Dublin area, this area has been modelled as 1D-2D using the Infoworks ICM flexible mesh software. A number of catchments in the Greater Dublin area have legacy drainage network models constructed in InfoWorks CS. Survey data gathered as part of the CFRAM study has been augmented with culvert and manhole information from these GDSDS models to allow a more accurate line and gradient of pipe networks to be represented in the model. Comprehensive data collection of existing sewer network records and survey of culverted reaches was undertaken for the GDSDS in order to capture detail in complex drainage networks i.e. changes to internal diameter and gradient. Therefore OPW and RPS selected ICM use to allow better representation of culverted river networks and enable better utilisation of, and future integration with, the existing sewer network models. ICM also provides a very stable 2D modelling regime for coastal inundation modelling, therefore ICM models (driven by a MIKE21 coastal model) were used for Dublin Bay coastal AFAs, to provide a consistent approach throughout the Greater Dublin area, facilitating integration with existing models. In addition to the watercourses, the model also incorporates the entire Dublin Bay coastal frontage from Strand Road in Sutton to Merrion Strand at the southern end of Sandymount. However the focus of this report section is the River Liffey and Dublin Port area at the mouth of the River Liffey. The River Liffey has been modelled using a 1D-2D approach extending downstream to the entrance of Alexandra Basin in Dublin Harbour. From this location a 2D coastal inundation approach has been taken to model the flood risk to Dublin Harbour. (2) Model Reference: HA09_LIFF2C (3) AFAs included in the model: Dublin City (4) Primary Watercourses / Water Bodies (including local names): ID NAME 09LIFF LIFFEY 09BELL BELLEVUE MILL RACE IBE0600Rp00027 4.7.2 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL 09MILA MIL A (5) Software Type (and version): (a) 1D Domain: (b) 2D Domain: (c) Other model elements: Infoworks ICM v5 Infoworks ICM Flexible Mesh N/A 4.7.2 Hydraulic Model Schematisation (1) Map of Model Extents: MILA Bellevue Mill Race Figure 4.7.1: Map of model extents within Dublin City AFA Figure 4.7.1 illustrates the extent of the modelled catchment, river centre line, HEP locations and AFA extents as applicable. The lower Liffey model contains 1 Upstream Limit HEP, 1 Downstream Limit HEP and 1 Intermediate HEP and 3 Trib HEPs. (2) x-y Coordinates of River (Upstream extent): River Name x y LIFFEY 311995 234161 BELLEVUE MILL RACE 312390 234210 MILA 312515 234227 (3) Total Modelled Watercourse Length: 7.3 km IBE0600Rp00027 4.7.3 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL (4) 1D Domain only Watercourse Length: NA (5) 1D-2D Domain 7.3 km Watercourse Length: (6) 2D Domain Mesh Type / Resolution / Area: Flexible / 1m2 - 25m2 / 17km² (7) 2D Domain Model Extent: Figure 4.7.2: 2D Domain Model Extent Topography Overview Figure 4.7.2 represents the modelled extents and the general topography of the catchment within the 2D model domain. The ground elevation (based on LiDAR data used to generate a 2D flexible mesh) is shown to provide an overview of the modelled area topography. There was no further post processing of the data contained within the mesh required. Changes in the vertical scale of this map are outlined by the index; all levels have been set to OD Malin. Figure 4.7.3 provides an overview of the model schematisation. Figure 4.7.4 and Figure 4.7.5 show detailed views. The overview diagram covers the model extents, showing the surveyed cross-section locations, AFA boundary and river centre line. It also shows the area covered by the 2D model domain. These diagrams include the surveyed cross-section locations, AFA boundary and river centre. They also show the location of the critical structures if applicable, along with the location and extent of the links between the 1D and 2D models. IBE0600Rp00027 4.7.4 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL The upstream extent of the model of the Lower Liffey is Islandbridge Weir and extends to the entrance of Alexandra Basin at Dublin Port. The 2D extent of the Lower Liffey model covers the majority of the coastline of Dublin Bay, however the focus of this section of the hydraulics report is the Lower Liffey and