Santry Model

Eastern CFRAM Study HA09 Hydraulics Report - DRAFT FINAL Eastern CFRAM Study HA09 Hydraulics Report Santry Model DOCUMENT CONTROL SHEET Client OPW Project Title Eastern CFRAM Study Document Title IBE0600Rp0027_HA09 Hydraulics Report Model Name HA09_Sant1 Rev. Status Author Reviewed By Approved By Office of Origin Issue Date D01 Draft M.Houston S. Cullen G. Glasgow Belfast 25/02/2014 D02 Draft M.Houston S. Cullen G. Glasgow Belfast 02/07/2014 F01 Draft A. Sloan S. Patterson G. Glasgow Belfast 25/02/2015 F02 Draft A. Sloan S. Patterson G. Glasgow Belfast 13/08/2015 F03 Draft Final A. Sloan S. Patterson G. Glasgow Belfast 05/08/2016 IBE0600Rp0027 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 3.2.1 Review 2011 Review_F02 Eastern CFRAM Study Inception August 2012 IBE0600Rp0008_HA09 Inception 4.3.2 Report UoM09 Report_F02 Eastern CFRAM Study Hydrology September IBE0600Rp0016_HA09_Hydrology 7.2 Report UoM09 2013 Report_F01 Eastern CFRAM Study HA09 Liffey November 2001s4884- SC2 Survey Report v1 Various Survey Contract Report 2012 IBE0600Rp0027 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL 4 HYDRAULIC MODEL DETAILS 4.10 SANTRY MODEL 4.10.1 General Hydraulic Model Information (1) Introduction: The Eastern CFRAM Flood Risk Review (IBE0600Rp0001_Flood Risk Review) highlighted Santry as an AFA and the Santry River itself as a HPW for fluvial flood risk under the ECFRAM Study based on a review of historic flooding and the extents of flood risk determined during the Preliminary Flood Risk Assessment. The Santry watercourse is within HA09, but is independent from the main Liffey system and flows directly into Dublin Bay at Raheny, to the west of North Bull Island. The watercourse originates from the southern edge of Dublin Airport and drainage drawings supplied by Dublin Airport Authority indicate that the drainage system for the western portion of the southern runway and some car park hardstanding both discharge to the headwaters of the Santry through conventional piped drainage systems. The Santry watercourse has a narrow catchment and has no significant tributaries. The total catchment area of the model at the downstream extents (at Raheny) is 13.96km². The catchment is heavily urbanised (62%) and includes an attenuating structure and online storage pond at Santry Demesne to the south of Northwood Avenue. Dublin City Council has also recently installed a flow control structure at the Harmonstown Road bridge. The model can be considered to represent a gauged catchment with the Cadburys hydrometric gauging station (09102 – EPA) located approximately two thirds of the length of the river from Dublin Airport. The gauging station was not given a classification under FSU and the rating curve does not extend up to the range of the observed corresponding water level at Qmed. As such the gauging station cannot be 3 considered to have a high degree of certainty at flood flows. The observed Qmed of 3.37m /s is derived from only 11 complete hydrological years of data which again does not afford high statistical certainty. A rainfall run-off model has been developed of the contributing catchment to the Cadburys gauging station in order to simulate a longer AMAX series and increase confidence in the Cadburys gauged Qmed. The model was calibrated against the existing continuous flow record of the gauging station from 2001 to 2011 and utilises rainfall data from the hourly gauge at Dublin Airport as input data. The hourly rainfall gauge was used at Dublin Airport due to its location at the edge of the Santry catchment which is small and therefore has little spatial variation in meteorological conditions which would be captured by the rainfall radar also located at Dublin Airport. The rainfall run-off (NAM) model was calibrated to the period for which there is corresponding flow data and rainfall gauge data (2001 – 2010) and good calibration was achieved. Hourly rainfall information is available for the period of 1941 – 2010 and was input to the rainfall run-off IBE0600Rp00027 4.10 - 1 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL 3 model. Analysis of the simulated flow trace shows that the simulated Qmed from this period is 3.25m /s. This compares to values derived from catchment descriptor based methods at the gauge of 4.55m3/s and 2.53m3/s using IH124 and FSU methods respectively. Due to the catchment sizes the IH124 values have been retained and adjusted downwards based on the relationship between the NAM simulated and IH124 derived index flood flow values at the Cadburys gauging station. The entire length of the Santry model is a HPW and was 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, including Raheny AFA, to provide a consistent approach throughout the Greater Dublin area, facilitating integration with existing models. (2) Model Reference: HA09_SANT1 (3) AFAs included in the model: Santry (flows through Raheny AFA where coastal flood risk is addressed by a separate model) (4) Primary Watercourses / Water Bodies (including local names): SANTRY (5) Software Type (and version): (a) 1D Domain: (b) 2D Domain: (c) Other model elements: Infoworks ICM Infoworks ICM v5 Flexible Mesh N/A 4.10.2 Hydraulic Model Schematisation (1) Map of Model Extents: Figure 4.10.1 illustrates the extent of the modelled catchment, river centre lines, HEP locations and AFA extents as applicable. The Santry modelled watercourse lies within the Dublin AFA and includes 1 Upstream Limit HEP, 1 Downstream Limit HEP, 1 Intermediate HEP and 1 Gauging Station HEP. There are no Tributary HEPs along this watercourse. IBE0600Rp00027 4.10 - 2 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Figure 4.10.1: Santry HPW/AFA Modelled Catchment and HEPs (2) x-y Coordinates of River (Upstream extent): River Name x y SANTRY 313968 242314 (3) Total Modelled Watercourse Length: 11.1 km (4) 1D Domain only Watercourse Length: N/A (5) 1D-2D Domain 11.1 km Watercourse Length: (6) 2D Domain Mesh Type / Resolution / Area: Flexible Mesh / 1-25 m2 / 13.7 km2 (7) 2D Domain Model Extent: Figure 42 shows the modelled extents and the general topography of the catchment within the 2D model domain. The river centre-line is shown in blue, changes in the vertical elevation of this map are outlined by the legend, all levels have been set to OD Malin (metres). 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. IBE0600Rp00027 4.10 - 3 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Figure 4.10.2: 2D Domain Model Extent IBE0600Rp00027 4.10 - 4 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Figure 4.10.3 is an overview of the model schematisation. Figure 4.10.4-4.10.6 show detailed views. The overview diagram covers the model extents, showing the cross-section locations, AFA boundary and river centre line. It also shows the area covered by the 2D model domain. The detailed areas are provided where there is the most significant risk of flooding. These diagrams include the surveyed cross-section locations, AFA boundary and river centre. They also show the location of the critical structures as discussed in Section 4.10.3, along with the location and extent of the links between the 1D and 2D models. Figure 4.10.3: Overview of Model Schematisation IBE0600Rp00027 4.10 - 5 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Figure 4.10.4: Model Schematisation in the vicinity of Harmonstown Road Flow Control Structure IBE0600Rp00027 4.10 - 6 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL Figure 4.10.5: Model Schematisation in the vicinity of Cadbury's Gauging Station Figure 4.10.6: Model Schematisation in the vicinity of Santry Attenuation Ponds (8) Survey Information (a) Survey Folder Structure: First Level Folder Second Level Folder Third Level Folder Murphy_E09_M01_WP2_120622_Santry_A GIS and Floodplain Structure Register Where: Photos Murphy – Surveyor Name Surveyed Cross Section Lines E09 – Eastern CFRAM Study Area, Photos Hydrometric Area 09 M01 – Model Number 1 Videos WP2 – Work Package 2 120622 – Date Issued (22nd June 2012) Ascii Santry_A – River Reference Drawings and PDFs (b) Survey Folder References: SANTRY Murphy_E09_M01_WP1_120504_SANT_Santry Gauge Murphy_E09_M01_WP2_120622_Santry_A Murphy_E09_M01_WP2_120622_Santry_B 2m resolution LiDAR of the entire modelled area was used to generate the 2D domain computational IBE0600Rp00027 4.10 - 7 Rev F03 Eastern CFRAM Study HA09 Hydraulics Report – DRAFT FINAL flexible mesh. The vertical accuracy of the LiDAR is quoted as 0.2m RMSE which was considered satisfactory for model application. A comparison of topographical survey levels along James Larkin Road and the LiDAR data for the same area was undertaken.

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