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Eastern CFRAM Study HA09 Hydraulics Report - DRAFT FINAL

IBE0600Rp0027 F03

DOCUMENT CONTROL SHEET

Client OPW

Project Title Eastern CFRAM Study

Document Title IBE0600Rp0027_HA09 Hydraulics Report

Model Name Maynooth

Rev.

Status Author(s) Modeller Reviewed by Approved By Office of Origin Issue Date

D01 Draft T. Carberry D. Irwin S. Patterson G. Glasgow Belfast 30/05/2014

F01 Draft Final

T. Carberry D. Irwin S. Patterson G. Glasgow Belfast 25/11/2014

F02 Draft Final


F03 Draft Final


Eastern CFRAM Study

HA09 Hydraulics Report –

Maynooth Model


IBE0600Rp0027 F03

Table of Reference Reports

Report Issue Date Report Reference Relevant Section

Eastern CFRAM Study Flood Risk Review

December 2011

IBE0600Rp0001_Flood Risk Review_F02

3.5.14

Eastern CFRAM Study Inception Report UoM09

August 2012 IBE0600Rp0008_HA09 Inception Report_F02

4.3.2, 4.4.3

Eastern CFRAM Study Hydrology Report UoM09

September 2013

IBE0600Rp0016_HA09_Hydrology Report_F01

4.9

Eastern CFRAM Study HA09 Liffey Survey Contract Report

November 2012

2001s4884- SC2 Survey Report v1 1.7.1


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4 HYDRAULIC MODEL DETAILS

4.18 MAYNOOTH

4.18.1 General Hydraulic Model Information

(1) Introduction:

The Eastern CFRAM Flood Risk Review (IBE0600Rp0001_Flood Risk Review) highlighted Maynooth in

the Liffey catchment as an Area for Further Assessment for fluvial flooding based on a review of historic

flooding and the extents of flood risk determined during the PFRA.

The Maynooth model represents the portion of the Rye Water, a large tributary of the Liffey, where it

passes through the Maynooth AFA. The model also represents the main tributary of the Rye Water, the

Lyreen River and a number of tributaries that flow into the Lyreen through Maynooth. The total catchment

represented by the model is 195 km2 with 88 km2 of the catchment area made up by the Lyreen which

joins the Rye Water just north of the town.

Both the Rye Water and the Lyreen are gauged within the model extents. The data available for flood flow

estimation at both gauges is of a similar quality and duration with both gauges having been installed in

2001 and operated by the EPA since. The Anne's Bridge gauging station (09048 – EPA) is located at the

upstream extents of the model on the Rye Water. The gauging station stage discharge rating relationship

is heavily extrapolated at the FSU estimated Qmed value based on catchment descriptors of 8.2 m3/s. Due

to the high uncertainty in the rating at flood flows and the short record length (10 complete years AMAX

data with some gaps) there is low confidence in the Qmed value of 22.9 m3/s derived from the gauging

station record. A catchment run-off (NAM) model has been developed of the gauged catchment and

calibrated against the low to mid range continuous flow trace at the Anne's Bridge gauging station using

gauge adjusted radar based hourly rainfall sums for the catchment from 2001 to 2010. Using the adjusted

radar based rainfall sums and observed rainfall sums from surrounding rain gauges a continuous flow

trace was simulated for the period 1950 to 2010. An AMAX series was extracted from the continuous flow

trace and the simulated Qmed calculated to be 17.0 m3/s.

The Lyreen is gauged at its downstream reach, approximately 0.5km upstream of its confluence with the

Rye Water at Maynooth (09049 – EPA). Similar to the Anne's Bridge gauging station the stage discharge

rating relationship is heavily extrapolated at the FSU estimated Qmed value based on catchment

descriptors of 10.0 m3/s. Due to the high uncertainty in the rating at flood flows and the short record length

(10 complete years AMAX data with some gaps) there is low confidence in the Qmed value of 25.8 m3/s

derived from the gauging station record. A catchment run-off (NAM) model has been developed of the

gauged catchment and calibrated against the low to mid range continuous flow trace at the Maynooth

gauging station using gauge adjusted radar based hourly rainfall sums for the catchment from 2001 to

2010. Using the adjusted radar based rainfall sums and observed rainfall sums from surrounding rain

gauges a continuous flow trace was simulated for the period 1964 to 2010. An AMAX series was extracted


IBE0600Rp0027 4.18-2 F03

from the continuous flow trace and the simulated Qmed calculated to be 12.4 m3/s.

Although both simulated Qmed values are affected by any uncertainty in the observed flow record at the

gauging station (through calibration of the NAM model) they are considered improved estimates of Qmed at

the gauging stations due to the longer record length, the quality of the rainfall and catchment data and the

availability of the flow records for calibration. There still remains however a striking difference between the

simulated values and those derived from the catchment descriptor based FSU approach, ranging between

20% and 110%, and it still remains a possibility that the poor record (and potentially grossly overestimating

rating curves) has skewed the simulation despite the best efforts to focus the calibration on low to mid

range flows. It is worth noting though that at the gauging station on the Rye Water downstream at Leixlip

(09001 – OPW) the difference between the observed Qmed and the Qmed derived from catchment

descriptors is approximately 35%. Considering the quality of the data at this station it can be considered

that there is definitely an underestimation using the FSU catchment descriptor based equation when

considering the Rye Water catchment and it is possible that the error is most pronounced upstream of the

Anne's Bridge gauging station (09048).

No gauging station rating reviews were proposed for these stations and as such it was considered prudent

that both of these simulated Qmed values were reviewed at hydraulic model calibration stage. The

comparison of the calibrated model Q-h relationship to the extrapolated rating curve at both stations would

indicate that the existing rating curves overestimate the Qmed value. This therefore provides some

validation for the simulated Qmed value from the rainfall runoff (NAM) models.

All watercourses in this model have been identified as HPW except the middle segment of the Ballybrack/

Roestown tributary between cross-sections 09ROES00425 at chainage 2391 and 09ROES00109 at

chainage 5525. A number of areas within the Rye Water and Lyreen catchments are relatively flat and

were considered to have potential for complex flood mechanisms, so it was decided to model all

watercourses as 1D-2D using the MIKE suite of software where LiDAR data was available. As a result,

approximately 500m of watercourse at the upstream extent of the Ballybrack/ Roestown tributary was

modelled as 1D only as LiDAR data was not available in this area. The water level was not found to reach

the bank markers in this location, so this approach was considered to be appropriate.

(2) Model Reference: HA09_MAYN4

(3) AFAs included in the model: Maynooth

(4) Primary Watercourses / Water Bodies (including local names):

Reach ID

09RYEW

09LYRE

09BBRK

09MILF

Name

Rye Water

Lyreen River

Ballybrack/ Roestown

Mill Race F


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09MILG

09MILK

09ROOS

09CREW

09MOYC

09MOYG

Mill Race G

Mill Race K

Roosk (known locally as Meadowbrook Stream)

Crewhill

Moyclare

Moygaddy

(5) Software Type (and version):

(a) 1D Domain :

MIKE 11 (2011)

(b) 2D Domain:

MIKE 21 - Rectangular Mesh

(2011)

(c) Other model elements:

MIKE FLOOD (2011)

4.18.2 Hydraulic Model Schematisation

(1) Map of Model Extents:


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Figure 4.18.1: Maynooth Model Overview


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Figure 4.18.2: Maynooth AFA Extent


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Figure 4.18.1 and Figure 4.18.2 illustrate the extent of the modelled catchment, river centre line, HEP

locations and AFA extents as applicable. The Rye Water/ Lyreen catchments contain 6 Upstream Limit

HEPs and 2 gauging station HEPs, one of which acts as an upstream limit point (09048_RPS). There are

also 2 intermediate HEPs, 1 Downstream Limit HEP and 7 Trib HEPs (6 of which are modelled

tributaries).

(2) x-y Coordinates of River (Upstream extent):

Table 4.18.1: x-y Coordinates of River

River Name x y

09RYEW Rye Water 290829.5 239322

09LYRE Lyreen River 291222 236735

09BBRK Ballybrack/ Roestown 286310.5 237246.5

09MILF Mill Race F 292510 237681.5

09MILG Mill Race G 293368 237730

09MILK Mill Race K 292690.5 237673.5

09ROOS Roosk 292780.5 235598.5

09CREW Crewhill 292209.5 238893.5

09MOYC Moyclare 292710 240221.5

09MOYG Moygaddy 294964.5 239570

(3) Total Modelled Watercourse Length: 22.9 km (approx.)

(4) 1D Domain only Watercourse Length: 0.5 km

(approx.)

(5) 1D-2D Domain

Watercourse Length:

22.4 km

(approx.)

(6) 2D Domain Mesh Type / Resolution / Area: Rectangular / 5 metres

72.6 km2 (approx.)

(7) 2D Domain Model Extent:


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Figure 4.18.3: 2D Model Grid


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Figure 4.18.4 2D Model Grid AFA Detail

Figure 4.18.3 and Figure 4.18.4 illustrate the modelled extents and the general topography of the

catchments.

Figure 4.18.5 shows an overview drawing of the model schematisation. Figure 4.18.6 to Figure 4.18.11

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. 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 4.18.3(1), along with the location and extent

of the links between the 1D and 2D models.


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Figure 4.18.5: Model Schematisation Overview

Figure 4.18.6: Detailed Area of Model Schematisation showing Critical Structures


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(8) Survey Information

(a) Survey Folder Structure:

First Level Folder Second Level Folder Third Level Folder

Murphy_E09_M04_WP3_120515_09MILF

Maynooth

Murphy: Surveyor Name

E09: Eastern CFRAM Study Area,

Hydrometric Area 9

M04: Model Number 4

09MILF: River Reference

WP3: Work Package3

Version: Most up to date

120515: Date Issued (15th MAY 2012)

SS 09MILF_V1_Ascii

V1_09MILF_GIS and

Floodplain Photos

Flood_Plane_Photos_and_Sha

pefiles

V2_09MILF_XS

Drawings & PDFs

4163_09MILF_Mill F_V2

Photos (Naming

convention is in the

format of Cross-Section

ID and orientation -

upstream, downstream,

left bank or right bank)

(b) Survey Folder References: Reach ID Name File Ref.

09RYEW Rye Water Murphy_E09_M05_WP3_120607_09RYEW_C

Murphy_E09_M04_WP3_130315_09RYEW_D


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Murphy_E09_M04_WP3_120619_09RYEW_E

Murphy_E09_M03A_WP5_120801_09RYEW_F

09LYRE Lyreen River Murphy_E09_M04_WP3_130315_09LYRE_A

Murphy_E09_M04_WP3_120619_09LYRE_B

09BBRK Ballybrack/ Roestown Murphy_E09_M04_WP3_120619_09BBRK

Murphy_E09_M04_WP3_120629_09ROES_A

Murphy_E09_M04_WP3_120607_09ROES_B

09MILF Mill Race F Murphy_E09_M04_WP3_120515_09MILF

09MILG Mill Race G Murphy_E09_M04_WP3_120515_09MILG

09MILK Mill Race K Murphy_E09_M04_WP3_120515_09MILK

09ROOS Roosk Murphy_E09_M04_WP3_120607_09ROOS

09CREW Crewhill Murphy_E09_M04_WP3_120607_09CREW

09MOYC Moyclare Murphy_E09_M04_WP3_120619_09MOYC

09MOYG Moygaddy Murphy_E09_M04_WP3_120619_09MOYG

(9) Survey Issues:

Initial attempts to calibrate the model to the Maynooth gauging station (09049) suggested an error in the

survey of the weir crest at this gauge. The original survey data received for section 09LYRE00041W

showed that the lowest point of the weir was at the right bank and had a crest level of 46.831mOD Malin.

Photos of the structure at low flow suggested it was a V-shaped structure and the records of EPA who

operate the station state that the lowest point of the crest is 46.691mOD Malin. A request was therefore

made to have this section re-surveyed, and revised data was delivered on 15/03/2013 which stated that

the invert level of the weir crest was 46.685mOD Malin.

A similar issue was experienced at the Anne's Bridge gauging station (09048) where the original survey

data received showed the lowest point of the weir crest 09RYEW00978W at the right bank and at a level

of 50.470mOD Malin. This was in contrast to photos suggesting the structure was V-shaped and EPA

records which state the lowest point of the crest is 50.259mOD Malin. This section was also re-surveyed

and revised data was delivered on 15/03/2013 which stated that the invert level of the weir crest was

50.206mOD Malin.

The 2D domain was derived using Lidar data as described in section 2.2.2, and no localised post-

processing of this data was carried out.

4.18.3 Hydraulic Model Construction

(1) 1D Structures (in-channel along See Appendix A.2


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modelled watercourses): Number of Bridges and Culverts: 63

Number of Weirs: 11

On the Lyreen River, the inverted siphon culvert 09LYRE00314I doesn't have sufficient capacity to convey flow

during flood events of 10% AEP or greater, resulting in widespread out-of-bank flooding and ponding upstream

of the culvert inlet. Refer to Appendix A.3 for further discussion on the complex hydraulic effect of this structure.

The preliminary report review "Lyreen River Flood Relief Scheme" states that an underwater video survey of this

structure was undertaken in 2001. A number of farm posts were lodged in the culvert and a barrel or concrete

pipe could be seen at one location. There were also air pockets in the soffit, however the culvert was reported to

be relatively free of silt. It is not know what the current condition of the structure is. Note the inlet is submerged in

Figure 4.18.12. No surveyed cross-section was taken at the upstream face of this structure, so the location of the

downstream face 09LYRE00311J is shown on Figure 4.18.6.

Figure 4.18.12: Inverted Siphon Culvert 09LYRE00314I

On the Ballybrack/ Roestown tributary, culvert 09ROES00281I and bridge 09ROES00228D do not have

sufficient capacity to convey flow during flood events of 10% AEP or greater, resulting in flooding in the Laragh

area which affects roads and properties.


IBE0600Rp0027 4.18-15 F03

Figure 4.18.13: Culvert 09ROES00281I (left) and Bridge 09ROES00228D (right)

On the Roosk watercourse, bridge 09ROOS00203D restricts flow and causes out-of-bank flooding during design

runs of 1% AEP or greater. This flooding affects agricultural land, local roads and a small number of properties.

Figure 4.18.14: Bridge 09ROOS00203D

On the Roosk watercourse, culvert 09ROOS00148I does no't have sufficient capacity to convey flow during

design runs of 1% AEP or greater, resulting in flooding of the Meadowbrook area. Up to approximately 90


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properties in Meadowbrook were found to be at risk during the 0.1% AEP design run.

Figure 4.18.15: Culvert 09ROOS00148I

On the Roosk watercourse, culvert 09ROOS00029I becomes surcharged during design runs of 0.1% AEP,

resulting in the wall defence on both sides of the watercourse upstream being overtopped. This flooding affects

the road at Parson Street, approximately 15-20 properties and a sports ground.


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Figure 4.18.16: Culvert 09ROOS00029I

On the Moyclare tributary, bridge 09MOYC00048D and culvert 09MOYC00023I do not have sufficient capacity to

convey flow during flood events of 10% AEP or greater, resulting in flooding of local roads and agricultural land.

Figure 4.18.17: Bridge 09MOYC00048D (left) and Culvert 09MOYC00023I (right)

The weir 09RYEW00628W at chainage 12997 on the Rye Water restricts outflow from the lake at Carton

Demesne. This flow restriction contributes to significant flooding upstream on the Rye Water during design runs


IBE0600Rp0027 4.18-18 F03

of 10% AEP or greater. A total of 9 cross-sections were surveyed between the upstream extent of the lake at

Carton Bridge (09RYEW00723D at chainage 12061) and weir 09RYEW00628W downstream. Given the

relatively high resolution of cross-sections, it was considered appropriate to model the lake as part of the Rye

Water 1D branch. Whilst a higher level of detail could be gained from undertaking a full bathymetric survey of the

lake this process, which involves interpolation between cross-sections, is a suitable methodology for

representing the hydraulic behaviour of the lake.

It should also be noted that the lake was assumed to be full at the start of the model simulation, based on

conditions where all watercourses in the model were set to baseflow.

Figure 4.18.18: Weir 09RYEW00628W


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Figure 4.18.19: Carton Demesne Lake

(2) 1D Structures in the 2D domain

(beyond the modelled watercourses):

None

(3) 2D Model structures: None

(4) Defences:

Type Watercourse Bank Model Start Chainage

(approx.)

Model End Chainage

(approx.)

Formal, Wall Roosk Both 2168 2325

(5) Model Boundaries - Inflows:

Full details of the flow estimates are provided in the Hydrology Report (IBE0600Rp0016_HA09 Hydrology

Report_F01 - Section 4.9 and Appendix D). The boundary conditions implemented in the model are shown as

follows.

Table 4.18.2: Model Boundary Conditions

Weir 09RYEW00628W

Carton Bridge 09RYEW00723D


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Note that Anne's Bridge Gauging station 09048 (adopted as the upstream limit point for this model) is located at

model chainage 9491 on the Rye Water. However, in line with standard modelling practice approximately 2.5km

of additional surveyed watercourse upstream of this point has been incorporated into the model to act as a

'warm-up' area. The inflow hydrograph for HEP 09048_RPS has therefore been input at model chainage 6978 as

this is the upstream model limit of the Rye Water branch. This has no influence on model results as the 'warm-

up' area is not mapped or reported, and model flows at HEP 09048_RPS were checked to ensure no loss of flow

had occurred.

In order to achieve the correct frequency conditions at the downstream checkpoint (09_1260_4_RPS), the input

hydrograph timings were altered, as per guidance in FSU WP3.4. Initial model runs considered the hydrograph

peaks from the Rye Water and Lyreen catchments occurring at the same time e.g. a 1% AEP flood event in both

catchments coinciding. These conditions resulted in the model flow at the downstream checkpoint

09_1260_4_RPS being considerably higher than the hydrological estimate as the flood frequency of this joint

condition is considerably more extreme than 1% AEP. The timing of the Rye Water and Lyreen catchment inputs

were therefore adjusted in order to create accurate flood frequency conditions at the downstream checkpoint

based on the joint probability of the two catchments. This involved delaying every input except the upstream and

lateral inflows to the Rye Water (09049_RPS and lateral inflow between 09049_RPS & 09_1260_4_RPS). Due

to the nature of the flood frequency conditions between the Rye Water and Lyreen catchments, the time the

Lyreen catchment inputs were delayed for increased as the flood frequency decreased.

Figure 4.18.20 provides an example of the associated upstream hydrographs on the Rye Water and Lyreen

River at HEPs 09048_RPS and 09_1452_2_RPS respectively during a 1% AEP design run.


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Figure 4.18.20: Inflow hydrograph at HEPs 09048_RPS and 09_1452_2_RPS during 1% AEP design run

(6) Model Boundaries –

Downstream Conditions:

A Q-h relationship boundary was applied at the downstream model extent of the

Rye Water (chainage 15883.462). This relationship is based on critical flow

conditions at this location, and is plotted below.


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Figure 4.18.21: Q-h relationship at Rye Water Ch. 15883

(7) Model Roughness: (see Section 3.5.1 'Roughness Coefficients')

(a) In-Bank (1D Domain) Minimum 'n' value: 0.021 Maximum 'n' value: 0.100

(b) MPW Out-of-Bank (1D) Minimum 'n' value: 0.045 Maximum 'n' value: 0.060

(c) MPW/HPW Out-of-Bank

(2D)

Minimum 'n' value: 0.013

(Inverse of Manning's 'M')

Maximum 'n' value: 0.065

(Inverse of Manning's 'M')


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Figure 4.18.22: Map of 2D Roughness (Manning's n)

This map illustrates the roughness values applied within the 2D domain of the model. Roughness in the 2D

domain was applied based on land type areas defined in the Corine Land Cover Map with representative

roughness values associated with each of the land cover classes in the dataset.

(d) Examples of In-Bank Roughness Coefficients

Lyreen River - 09LYRE00120_DN Rye Water - 09RYEW00742_DN


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Figure 4.18.23: 09LYRE00120_DN

Manning's n = 0.035

Natural stream - clean, straight, some stones and

weeds.

Figure 4.18.24: 09RYEW00742_DN

Manning's n = 0.030

Natural stream - clean, straight, full stage, no rifts or

deep pools.

Ballybrack/ Roestown - 09BBRK00021_UP

Figure 4.18.25: 09BBRK00021_UP

Manning's n = 0.050

Natural stream - clean, winding, notable stones and

weeds.

Crewhill - 09CREW00032_DN

Figure 4.18.26: 09CREW00032_DN

Manning's n = 0.035

Natural stream - clean, straight, some stones and

weeds.

4.18.4 Sensitivity Analysis

To be completed at Final version.


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4.18.5 Hydraulic Model Calibration and Verification

(1) Key Historical Floods (from IBE0600Rp0008_HA09 Inception Report_F02 unless otherwise specified):

Aug 2008. The historical data indicated that flooding occurred in Co. Kildare in August 2008 as a

result of heavy and prolonged rainfall. No details were available relating to any damage

caused in Maynooth as a result of the August 2008 flood event. The daily mean flow rate of

the River Lyreen (as per http://hydronet.epa.ie) was measured to be 49m3/s at Maynooth

Hydrometric Station, and is also the maximum daily mean flow rate on record for the River

Lyreen at this location. This measurement should be treated with caution however, as this

is well beyond the useable rating for this station.

An analysis of significant flood events at gauging stations 09048 and 09049 was

undertaken as part of the CFRAM study and a summary of the results can be found in

IBE0600Rp0008_HA09 Inception Report_F02 Section 4.4.3. The flood event in August

2008 was estimated at approximately 5-6.67% AEP at 09048 Anne's Bridge, and

approximately 6.67-10% AEP at 09049 Maynooth.

Design rainfall frequency was estimated using the FSU Depth Duration Frequency model

(FSU WP 1.2 ‘Estimation of Point Rainfall Frequencies’). The closest rainfall gauge with

data available for this event is Leixlip (Gen.Stn) daily station (approximately 6km

downstream of the AFA). Recordings from this station indicate that 87.4mm of rain fell on

the 9th August 2008, equating to a rainfall event of approximately 1.2% AEP. As this gauge

is not located within the AFA extents and only has a data recording resolution of 24 hours,

this rainfall frequency should be treated with caution. It does however provide support for

the estimated flood event frequency of 5-10% AEP derived from the analyses of significant

flood events at gauging stations 09048 and 09049. It should also be noted that a total of

151.8mm of rain was recorded between the 9-16th August, and it can be seen from gauge

records that multiple significant events occurred during this period.

The maximum observed water level at gauging station 09049 Maynooth on the Lyreen

River during the flood event of August 2008 equated to 48.279mOD Malin according to

gauge records. The maximum modelled water levels measured at chainage 3896 on the

Lyreen River (representing gauging station 09049) during the 10% and 1% AEP design

runs were 48.133mOD Malin and 48.514mOD Malin respectively. The observed

hydrograph from this event is plotted in Figure 4.18.27, along with the modelled

hydrographs from the 10% and 1% AEP design runs. The model shows good calibration at

this point, as the flood event frequency was estimated at approximately 6.67-10% AEP

from gauge records and the observed peak water level is between the 10% and 1% AEP

design run peak water levels. It can be seen from Figure 4.18.27 that the observed and


IBE0600Rp0027 4.18-26 F03

modelled hydrographs are similar in terms of shape and time-to-peak, providing further

verification for the model results.

Figure 4.18.27: Observed and modelled hydrographs at gauging station 09049

Maynooth

The maximum observed water level at gauging station 09048 Anne's Bridge on the Rye

Water during the flood event of August 2008 equated to 51.901mOD Malin. The maximum

modelled water levels measured at chainage 9482 on the Rye Water (representing

gauging station 09048) during the 10% and 1% AEP design runs were 51.940mOD Malin

and 52.124mOD Malin respectively. The observed hydrograph from this event is plotted in

Figure 4.18.28, along with the modelled hydrographs from the 10% and 1% AEP design

runs. The AEP of this flood event was originally estimated at approximately 5-6.67%, so

the levels shown in the model are slightly high. Confidence in the estimated flood

frequency is low however and the event may be overestimated due to the relatively short

period of data available. It is reasonable to expect that the AEP of this flood event may

have been approximately 10% on the Rye Water catchment, as displayed by the model, so

reasonable model verification has been achieved. It can also be seen from Figure 4.18.28

that the observed and modelled hydrographs are similar in terms of shape and time-to-

peak, providing further verification for the model results.


IBE0600Rp0027 4.18-27 F03

Figure 4.18.28: Observed and modelled hydrographs at gauging station 09048

Anne's Bridge

Nov 2002. Widespread flooding occurred in mid November 2002 as a result of heavy and prolonged

rainfall. Flooding was severe in some parts as the catchments were already somewhat

saturated, following high levels of rainfall in October and early November. The total rainfall

depth measured at Dublin Airport during this event was 87mm, while 72mm of rainfall was

recorded at Casement.

Maynooth experienced flooding in many parts as a result of the heavy rainfall in November

2002. A ditch on Moyglare Road was blocked and flooded, as was a pipe on Laurence's

Avenue. Some roads flooded including the N4/M4, Moyglare Road, Dunboyne Road,

Kilcock Road and Laurence's Avenue. Sandbags were distributed throughout the area

thereby reducing the damage caused to houses.

The analysis of significant flood events at gauging stations 09048 and 09049 estimated the

flood event in November 2002 at approximately 50% AEP at both locations. There is

considerable uncertainty in these values however as both recorders failed during this

event, so the peak water level and flow was not captured. Data from these gauging

stations was therefore not used for model calibration or verification for this event.

Design rainfall frequency was estimated using the closest rainfall gauge with data available

for this event. This was Leixlip (Gen.Stn) daily station (approximately 6km downstream of


IBE0600Rp0027 4.18-28 F03

the AFA). Recordings from this station indicate that 74.0mm of rain fell between the 13-14th

November 2002, equating to a rainfall event of approximately 6-7.5% AEP.

The reports of flooding at the Moyglare Road, Dunboyne Road and Laurence's Avenue all

refer to flooding from pluvial sources, and are therefore not suitable for model calibration.

Flooding occurs within the model on the Kilcock Road during design runs of 1% AEP or

greater, as shown in Figure 4.18.29 below. It is unlikely that this flood event had a

frequency as severe as 1% AEP, however the document which reports flooding at this

location (Maynooth Area Engineer Meeting - Minutes) suggests that remedial work has

been carried out further altering the validity of this event for model calibration.

Figure 4.18.29: Kilcock Road Flooding

The exact location of flooding of the N4/M4 during this event is not specified. Flooding was

only found to occur on the N4/M4 during model design runs of 1% AEP or greater, and this

flood event is not considered to be of that magnitude. It is likely that flooding occurred on

this motorway due to drainage design capacity being unable to cope with the intense

rainfall associated with this event, therefore this flooding would not be represented by the

model. Data from this flood event was therefore not used for model calibration or

verification.

Nov 2000. Extensive flooding occurred throughout large parts of Dublin and Kildare in November

2000 as a result of heavy rainfall, high tides and strong winds.

Kilcock Road Flooding

Lyreen River


IBE0600Rp0027 4.18-29 F03

The high levels of rainfall adversely affected Maynooth in November 2000 causing the

Royal Canal, Meadowbank Stream and Lyreen River to burst their banks. The lack of

capacity of the Railway Culvert on the Lyreen River caused the Treadstown Road, Railway

Line (at Jackson's Bridge) and surrounding lands to flood. Lands adjacent to the Ryewater

River were also flooded. Damage to houses was limited through the distribution of

sandbags which were used to divert floodwaters. However, flooding did occur in

Meadowbrook estate with approximately 40 houses affected and also on Parson Street

where eight houses were flooded. The N4 and Clane-Maynooth road were closed due to

the floods, as were many streets in the Maynooth area and a local pumping station was

also inundated by floodwaters. No details were available on return period or flows for this

flood event.

Design rainfall frequency was estimated for this event in the absence of hydrometric data

as both gauging stations 09048 and 09049 were installed in 2001. Leixlip (Gen.Stn) daily

station (approximately 6km downstream of the AFA) recorded 102.6mm of rain between

the 5-6th November 2000, equating to a rainfall event of approximately 1.3-1.7% AEP.

Barrockstown daily station (approximately 3km North of the AFA) also has data available

for this flood event, recording 87.8mm of rain between the 5-6th November 2000. This

equated to a rainfall event of approximately 1.6-2.1% AEP.

Aerial photos from this event are available and these have been used for model verification

where possible. The location of a number of photos could not be established. A

comparison of model results and these photos is shown below. Overall good model

verification was achieved as the flood extents seen in the photos was generally between

the model 1% and 10% AEP design run extents. One notable exception to this is in the

Meadowbrook area, where flooding was found to occur in the model during design runs of

1% AEP or greater. Newspaper articles suggest that the M4 motorway drains to this

stream, and that this was a major factor contributing to the severe flooding in November

2000. The flooding in this area is therefore partly due to a pluvial source, so it is expected

that the model flood extents would not be as severe.

The Roosk tributary that runs through the Meadowbrook area also appears to have been

altered since November 2000. It can be seen in Figure 4.18.33 that new roads have been

constructed in this area, and this has required the construction of culverts to accommodate

these works. It is not known what consideration was made to the existing watercourse

during these plans, and if any remedial works were carried out.

Parson Street, as shown in Figure 4.18.33, was reported to have flooded, with 8 adjacent

properties affected. The wall adjacent to the Roosk watercourse at Parson Street was

found to have a SoP of 1% AEP, so flooding in this area was only found to occur during

defended design runs of 0.1% AEP. The modelled extent of the benefitting area from this


IBE0600Rp0027 4.18-30 F03

defence is similar to the observed flood extent from November 2000 however, as shown in

Figure 4.18.34. No information is available regarding the effectiveness of this defence

during this event, but it is possible that a breach may have occurred. As this information is

not known, this cannot be used for model calibration, however it does provide limited

qualitative support for the model results.


IBE0600Rp0027 4.18-31 F03

Figure 4.18.30: Flooding at Rye Water/ Lyreen Confluence

Figure 4.18.31: Flooding at Carton Estate

Direction of photo

Fish Farm

Direction of photo

Direction of photo

Figure 4.18.32

Direction of photo

Figure 4.18.33

Roosk tributary

Rye Water

Lyreen River

Rye Water


IBE0600Rp0027 4.18-32 F03

Figure 4.18.32: Flooding at Meadowbrook

Figure 4.18.33: Flooding downstream at Meadowbrook

Area with new road alignment

Parson Street

Sports ground


IBE0600Rp0027 4.18-33 F03

Figure 4.18.34: Benefitting Area at Parson Street

Direction of photo

Lyreen River

Ballybrack/ Roestown Jackson's Bridge

Railway/canal culvert

09RYEW00314I

Direction of photo

Figure 4.18.33

Parson Street

Sports ground

09ROOS00029I


IBE0600Rp0027 4.18-34 F03

Figure 4.18.35: Flooding at Jackson's Bridge

Figure 4.18.36: Flooding on the upper Lyreen

Jun 1993. Widespread flooding occurred across Dublin, Kildare and Wicklow as a result of prolonged

rainfall beginning on Friday 11th June and lasting for over two days.

In the Maynooth area, a culvert on the Lyreen River near Jackson's Bridge (crossing under

railway line and Royal Canal) lacked capacity and caused flooding of farmland both

upstream and downstream of the culvert. No additional information was provided, however

photographs from this event are available in the report "Lyreen River Flood Relief Scheme"

displaying the extent of the flooding.


(as gauging stations 09048 and 09049 were both installed in 2001). Leixlip (Gen.Stn) daily

station (approximately 6km downstream of the AFA) recorded 79.8mm of rain between the

10-11th June 1993, equating to a rainfall event of approximately 4.1-5.4% AEP.

Direction of photo

Lyreen River


IBE0600Rp0027 4.18-35 F03

The quality of photographs provided for this event is poor, and quantitative calibration is

not possible. The two photographs shown in Figure 4.18.37 below were originally

captioned as "Flooding in fields and passageway south-west of Jackson's Bridge" and

"Flooding immediately upstream of railway/canal culvert" in the "Lyreen River Flood Relief

Scheme" report. Although the exact extent cannot be compared, it can be seen in Figure

4.18.35 that widespread flooding occurs in the area described even during the 10% AEP

model design run, so good qualitative support for the model results has been achieved.

Figure 4.18.37: Flooding upstream of the railway/canal culvert on the Lyreen River

Nov 1965. The historical data indicated that severe flooding occurred in November 1965 following

three days of torrential rain.

The historical review indicated that a number of houses were flooded in Maynooth as a

result of the rainfall; however there is no indication of the exact quantity or location of such

houses.


(as gauging stations 09048 and 09049 were both installed in 2001). Leixlip (Gen.Stn) daily

station (approximately 6km downstream of the AFA) recorded 81.7mm of rain between the

16-18th November 1965, equating to a rainfall event of approximately 6.2-7.6% AEP.

As there is no further data available relating to the flood extents and damage caused by

this event, it was not considered suitable for calibration.


IBE0600Rp0027 4.18-36 F03

Summary of Calibration

The two hydrometric gauges within the model extent were both installed relatively recently, and therefore only

have reliable ratings for low flows. An analysis of significant flood events at each of these stations was

undertaken in order to quantify the flood events of August 2008 and November 2002, however these values

should be treated with caution due to the low number of events available for analysis.

Data from daily rainfall stations was also used to estimate the rainfall event return period using the FSU for

each historical event. Data was available at Leixlip (Gen.Stn) daily station for every flood event, and

Barrockstown daily station also had data available for the November 2000 event.

Model flows were checked against the estimated flows at HEP check points where possible to ensure they were

within an acceptable range. For example at HEP 09_1260_4_RPS, the estimated flow during the 1% AEP event

was 65.93m3/s and the modelled flow was 66.68m3/s. Full flow tables can be found in Appendix A.3.

A mass balance check has been carried out on the model to make sure that the total volume of water entering

and leaving the model at the upstream and downstream boundaries balances the quantity of water remaining in

the model domain at the end of a simulation. Refer to Chapter 3.11 for details of acceptable limits. The mass

error in the 1% AEP design run was found to be -1.38%, so the Maynooth model is considered to be robust and

stable.

The data available for historical flood events at Maynooth was generally good, and included a significant

number of aerial photographs taken shortly after the flood event in November 2000. This data was used to

provide good qualitative support for the model results. The model Q-h relationship was also calibrated to the

rating curves at hydrometric gauges 09048 and 09049, although it should be noted that these ratings are only

valid for low flows. Overall the model is performing well for design event simulation and is supported by historic

and hydrometric information.

(2) Post Public Consultation Updates:

At a draft flood mapping workshop held on 16/04/2014, Local Authorities suggested that the modelled flood

outlines were representative.

All recorded comments were investigated following informal public consultation and formal S.I. public

consultation periods in 2015, however no model updates were required for Final issue.

(3) Standard of Protection of Existing Formal Defences:

Defence

Reference

Type Watercourse Bank Modelled

Standard of

Protection (AEP)

1 Wall Roosk Both 1%

Figure 4.18.38 shows the location of all defences within the Maynooth AFA.


IBE0600Rp0027 4.18-37 F03

Figure 4.18.38: Maynooth AFA Defences

It can be seen in Figure 4.18.34 that the wall (Reference 1) offers protection to Parson Street and approximately

15-20 properties in the surrounding area. The sports ground adjacent to the Roosk tributary also benefits from

this defence. This wall has a modelled SoP of 1% AEP.

(4) Gauging Stations:

There are two gauging stations within the model extent, Anne's Bridge (09048) and Maynooth (09049) as

shown in Figure 4.18.39. Both stations are automatic data loggers with water level and flow data available at 15

minute intervals. Station 09048 was installed in May 2001 and station 09049 was installed in July 2001, and

both stations have data available up to May 2011. Station 09048 is located on the Rye Water and the estimated

flow at this point is used at the upstream extent of the model. Station 09049 is located on the Lyreen River,

approximately 400m upstream of its confluence with the Rye Water.

1

Roosk

Lyreen

Mill Race F

Royal Canal


IBE0600Rp0027 4.18-38 F03

Figure 4.18.39: Gauging Station locations within the Maynooth AFA

(a) Anne's Bridge (09048)

The rating for this gauging station is for low flows only (less than 2.5 m3/s) and is therefore uncertain for flood

flows. The rating is significantly less than the estimated Qmed of 16.96 m3/s. The survey provides a cross-section

at the gauge location - comparing the modelled Q-h relationship and the rating curve, as shown in Figure

4.18.40, it can be seen that reasonable model calibration to the existing rating curve has been achieved and the

two curves are within 200 mm of each other as required in the Project Brief for HPWs. It should be noted that a

Manning's n value of 0.011 at the weir was required in order to produce the Q-h relationship shown below. This

value is within the realistic range for this type of section i.e. concrete lined, but is at the lower end of the range.


IBE0600Rp0027 4.18-39 F03

Figure 4.18.40: Comparison of EPA rating curve with RPS Q-h relationship at Anne's Bridge gauging

station (09048)

(b) Maynooth (09049)

The rating for this gauging station is for low flows only (less than 5.2 m3/s) and is therefore uncertain for flood

flows. The rating is significantly less than the estimated Qmed of 12.40 m3/s. There were no spot gaugings

available at this station. The survey provides a cross-section at the gauge location - comparing the modelled Q-

h relationship and the rating curve, as shown in Figure 4.18.41, it can be seen that reasonable model calibration

to the existing rating curve has been achieved and the two curves are within 200 mm of each other as required

in the Project Brief for HPWs. It should be noted that a Manning's n value of 0.011 at the weir was required in

order to produce the Q-h relationship shown below. This value is within the realistic range for this type of

section i.e. concrete lined, but is at the lower end of the range.


IBE0600Rp0027 4.18-40 F03

Figure 4.18.41: Comparison of EPA rating curve with RPS Q-h relationship at Maynooth gauging station

(09049)

(5) Other Information:

(a) Maynooth Area Engineer Meeting - Minutes (2005) - Meeting with the Maynooth Area Engineer identifying

areas which are prone to flooding.

'Greenfield: Meadowbrook River overflowed its banks in November 2000. M4 motorway blocked.' - Flooding

from this tributary was only found to occur during design runs of 1% AEP or greater, as shown in Figure

4.18.32. As discussed earlier, there is a drainage issue from the M4 at this location and remedial works have

been carried out on this watercourse, so this information is not suitable for calibration.

'Ballycurraghan: River overflows bank after heavy rain every year' - The Ballybrack/ Roestown tributary was

found to flood during 10% AEP model design runs, as shown in Figure 4.18.42. This is consistent with the data

provided, so good qualitative support for the model results was achieved.


IBE0600Rp0027 4.18-41 F03

Figure 4.18.42: Flooding in the Ballcurraghan and Laragh areas

The other comments in this report are specific to the flood event in November 2002 and have been addressed

in section 4.18.5(1).

(b) Clane Area Engineer Meeting - Minutes (2005) - Meeting with the Clane Area Engineer identifying areas

which are prone to flooding.

'Laragh: Stream overflows its banks after heavy rain every year. Road is liable to flood.' - This area was found

to flood during design runs of 10% AEP or greater, as shown in Figure 4.18.42. This is consistent with the data

provided, so good qualitative support for the model results was achieved.

4.18.6 Hydraulic Model Assumptions, Limitations and Handover Notes

(1) Hydraulic Model Assumptions:

(a) The in-channel roughness coefficients were selected based on normal bounds using photographs

delivered as part of the channel and structure survey - it is considered that the final selected values are

representative.

(b) The hydrological inputs had to be edited in order to achieve the correct frequency conditions at the

downstream checkpoint, as per guidance in FSU WP3.4. This is discussed further in section 4.18.3(5).

(c) The upstream face of the Railway/ Canal culvert (09RYEW00314I) could not be surveyed as there

Road flooding

Ballycurraghan Ballybrack/ Roestown

09ROES00228D

09ROES00281I


IBE0600Rp0027 4.18-42 F03

was no access because of the railway line. This culvert was therefore modelled based on the downstream

surveyed dimensions and it was assumed that these were representative.

(d) No information regarding the Royal Canal was provided, and as no inlet/outfall positions were

recorded in the survey data it was assumed that the Royal Canal is hydraulically separate from the

modelled watercourses in Maynooth. No allowance for the Canal was made in the design hydrology. It

was therefore considered unrealistic to include the Royal Canal Arch of Jackson's Bridge

(09ROES00012D at chainage 6497 on the Ballybrack/ Roestown tributary, as shown in Figure 4.18.35), so

only the two main arches and the railway arch were included in the model. A survey drawing of this

structure is shown in Figure 4.18.43.

Figure 4.18.43: Survey drawing of 09ROES00012D Jackson's Bridge

(e) The bridges 09RYEW00267D and 09RYEW00266D on the Rye Water were modelled as a single

structure due to their close proximity and similar characteristics. This achieved greater model stability and

did not affect model results. This was also carried out with structures 09RYEW00237D and

09RYEW00236I on the Rye Water.

(f) The bridge 09MOYC00027D on Moyclare was not included in the model as this structure was not

found to cause a restriction to flow during any model design run, and greater model stability was achieved

through its omission.

(g) The bridge 09MILF00033D on Mill Race F was not included in the model as this structure was not

found to cause a restriction to flow during any model design run, and greater model stability was achieved

through its omission.

(h) The footbridge 09RYEW00629D on the Rye Water was not included in the model. An initial

assessment concluded that this bridge has very little hydraulic impact upon the flow regime, and the

bridge is located immediately upstream of weir 09RYEW00628W. It was not possible to integrate both

structures into the model and achieve good stability, and as the weir is more critical it was decided to omit

the bridge from the model.

(2) Hydraulic Model Limitations and Parameters:

(a) A grid resolution of 5 metres has been selected for the 2D domain. This cell size enables areas of

interest to be modelled in sufficient detail, whilst still retaining good computational performance of the

model.

Two Main Arches

Railway Arch

Royal Canal Arch


IBE0600Rp0027 4.18-43 F03

(b) There is a minor instability at bridge 09RYEW01011D at chainage 9185 on the Rye Water which

occurs on the receding limb of the flow hydrograph. It was not possible to eradicate this instability so a

review of its significance was undertaken. This instability occurs when the water level is in-bank and does

not cause erroneous out-of-bank flooding. As it occurs on the receding limb of the hydrograph it does not

affect the estimation of peak water levels or flows. It is also located on the 'warm-up' section of the Rye

Water, and as this section of the model is not used for design flood estimation its significance is low. In

addition, the mass error of the model is low, further supporting the conclusion that this instability is minor.

A plot of the flow and water level hydrographs at this point during the 0.1% AEP design run is shown in

Figure 4.18.44. It can be seen from this plot that the water level and discharge profiles are stable at the

peak, and while the discharge flickers sharply in the range of ±20m3/s, the maximum effect this has on

water level is ±100mm.

Figure 4.18.44: Water Level and Discharge profiles at Rye Water Ch. 9185 during 0.1% AEP design

run

Hydraulic Model Parameters:

MIKE 11

Timestep (seconds) 2

Wave Approximation High Order Fully Dynamic

Delta 0.85

MIKE 21

Timestep (seconds) 2

Drying / Flooding depths (metres) 0.02 / 0.03

Eddy Viscosity (and type) 0.25 (Flux based)

MIKE FLOOD

Discharge

Water Level


IBE0600Rp0027 4.18-44 F03

Link Exponential Smoothing Factor

(where non-default value used)

Rye Water, Ch 8876 - Ch 9391: 0.8

Rye Water, Ch 14474 - Ch 15174: 0.8

Lyreen, Ch 695 - Ch 1188: 0.8

Mill Race F, Ch 0 - Ch 1130: 0.8

Lateral Length Depth Tolerance (m)

(where non-default value used)

Rye Water, Ch 8876 - Ch 9391: 0.2

Rye Water, Ch 14474 - Ch 15174: 0.2

Lyreen, Ch 695 - Ch 1188: 0.2

(3) Design Event Runs & Hydraulic Model Handover Notes:

(a) The Cross-section and Network files are identical for all design run simulations. The parameters within

the HD parameter file are also identical.

(b) The hydrological inputs for the Lyreen catchment were delayed in every design run in order to achieve

the correct flood frequency conditions at the downstream checkpoint 09_1260_4_RPS as per guidance in

FSU WP3.4. Due to the nature of the flood frequency conditions between the two catchments, the time the

Lyreen catchment inputs were delayed for increased as the flood frequency decreased. As a result the

simulation times for each design run scenario are not identical.

(c) A hot start file has been used in the 1D model component during all design runs. This hotstart file

simulates baseflow conditions in all watercourses within the Maynooth model.

(d) Global surface elevation initial conditions of 0mOD Malin in the 2D domain have been used during all

design runs. As the minimum topographical level in the 2D domain is greater than 36mOD Malin, these

initial conditions mean the 2D domain is fully dry at the start of the simulation.

(e) The Railway/ Canal culvert on the Lyreen River (09LYRE00314I) was found to become surcharged

during design runs of 10% AEP or greater, resulting in severe flooding upstream as shown in Figure

4.18.35. This inverted siphon culvert lacks capacity, which causes both the Lyreen and Ballybrack/

Roestown channels to back-up upstream. A large area of agricultural land is affected, along with

approximately 5 properties and a local road. Flood depths in this area can reach over 2.2m during design

runs of 0.1% AEP and this land was found to remain flooded for approximately 3 days due to culvert

09LYRE00314I restricting flood waters from receding. The M4 motorway was also found to flood during

design runs of 1% AEP or greater. The large afflux of this culvert and its impact on peak water levels

upstream on the Lyreen River can be seen in Figure 4.18.53 in Appendix A.2.


IBE0600Rp0027 4.18-45 F03

Figure 4.18.45: Flooding due to Inverted Siphon Culvert 09RYEW00314I

(f) Flooding was found to occur at numerous locations on the Ballybrack/ Roestown tributary during

design runs of 1% AEP or greater due to insufficient channel capacity, as shown on Page 11 of the Draft

Final Extent Maps E09MAY_EXFCD001_010_100_C0. Flooding was also found to occur in the

Ballycurraghan and Laragh areas during 10% AEP design runs due to insufficient capacity of culverts

09ROES00281I and 09ROES00228D, as shown in Figure 4.18.42. This flooding affects agricultural land,

a local road and approximately 2-5 properties.

(g) Flooding was found to occur on the upper section of the Roosk tributary during design runs of 1% AEP

or greater due to insufficient capacity of bridge 09ROOS00203D. This flooding affects agricultural land,

local roads and approximately 2-5 properties, as shown in Figure 4.18.46.

09RYEW00314I

Alternative flow path

along canal

Lyreen

Ballybrack/ Roestown

Mill Race F

Road flooding

M4


IBE0600Rp0027 4.18-46 F03

Figure 4.18.46: Flooding on the upper Roosk tributary

(h) Flooding in the Meadowbrook area was found to occur during design runs of 1% AEP or greater, as

shown in Figure 4.18.47. The main cause of this flooding is insufficient capacity of culvert 09ROOS00148I,

however the Roosk tributary that runs through this area is heavily culverted, so may be prone to blockage.

There have also been historical issues in this area attributed to surface drainage from the M4 discharging

to this watercourse, therefore exacerbating the flood extents. Up to approximately 90 properties in the

Meadowbrook area were found to be at risk during the 0.1% AEP design run.

09ROOS00203D

Roosk

M4


IBE0600Rp0027 4.18-47 F03

Figure 4.18.47: Flooding in the Meadowbrook area

(i) Flooding was found to occur at Parson Street during design runs of 0.1% AEP as shown in Figure

4.18.34. This is due to culvert 09ROOS00029I becoming surcharged during this scenario, resulting in the

wall defence on both sides of the watercourse upstream being overtopped. This flooding affects the road

at Parson Street, approximately 15-20 properties and a sports ground.

(j) Considerable flooding was found to occur from the Moyclare watercourse during design runs of 10%

AEP or greater, as shown in Figure 4.18.48. This flooding was found to affect local roads and agricultural

land, but properties were not found to be at risk. The main cause of this flooding was insufficient capacity

in structures 09MOYC00048D and 09MOYC00023I.

09ROOS00148I

Meadowbrook

Roosk

M4


IBE0600Rp0027 4.18-48 F03

Figure 4.18.48: Flooding from the Moyclare watercourse

(k) The capacity of the Moygaddy watercourse channel was found to be insufficient to convey the 10%

AEP design flow without flooding of agricultural land occurring, especially close to its confluence with the

Rye Water. A local road was also found to be affected during flood events of 1% AEP or greater. No

properties were found to be at risk due to flooding from this watercourse.

Moyclare

Rye Water

09MOYC00048D

09MOYC00023I


IBE0600Rp0027 4.18-49 F03

Figure 4.18.49: Flooding from the Moygaddy watercourse

(l) Widespread flooding of land adjacent to the Rye Water channel was found to occur due to insufficient

channel capacity. Flooding was found to occur from both banks and was most prevalent during design

runs of 1% AEP or greater, but was still substantial during the 10% AEP design run as shown in Figure

4.18.50 and Figure 4.18.51. The main receptor to the flooding is agricultural land, although one local road

was also found to flood. One property was found to be affected during the 10% AEP design run, and up to

4 additional properties are affected during design runs of 0.1% AEP. The weir 09RYEW00628W is a

significant structure as it restricts the outflow from the lake at Carton Demesne. This restriction contributes

considerably to the widespread flooding upstream. The impact this weir has on peak water levels in the

lake at Carton Demesne and further upstream on the Rye Water is shown in Figure 4.18.52 in Appendix

A.2.

Moygaddy

Rye Water

Road flooding


IBE0600Rp0027 4.18-50 F03

Figure 4.18.50: Flooding from the upper Rye Water

Rye Water

Rye Water

Lyreen

Moyclare

Moygaddy

Road flooding

Carton Demesne lake

09RYEW00628W


IBE0600Rp0027 4.18-51 F03

Figure 4.18.51: Flooding from the lower Rye Water

(4) Hydraulic Model Deliverables:

Please see Appendix A.4 for a list of all model files provided with this report.

(5) Quality Assurance:

Model Constructed by:

Model Reviewed by:

Model Approved by:

David Irwin

Stephen Patterson

Malcolm Brian


IBE0600Rp0016 4.18-52 F03

APPENDIX A.1

Structure Details – Bridges and Culverts

RIVER BRANCH CHAINAGE ID LENGTH

(m) OPENING

SHAPE HEIGHT (m) WIDTH (m)

SPRING HEIGHT FROM

INVERT (m)

MANNING'S N

CREWHILL TRIB 761.3 09CREW00111D 4.2 Arch 0.54 0.58 0.26 0.023

CREWHILL TRIB 1194.2 09CREW00073I 85.4 Circular 0.6 N/A N/A 0.013

CREWHILL TRIB* 1365.0 09CREW00053I 89.0 Circular 0.6 N/A N/A 0.013

CREWHILL TRIB 1531.3 09CREW00036I 32.6 Circular x2 0.55 N/A N/A 0.020

CREWHILL TRIB 1628.6 09CREW00026I 2.6 Irregular 0.54 0.46 N/A 0.033

ROOSK TRIB 351.7 09ROOS00227D 3.4 Arch 1.68 1.76 1 0.023

ROOSK TRIB 585.6 09ROOS00203D 3.4 Arch 1.93 1.74 1.3 0.025

ROOSK TRIB 973.9 09ROOS00170I 59.6 Irregular 1.69 3.32 N/A 0.013



ROOSK TRIB 1205.5 09ROOS00141I 11.7 Circular x3 1.5 N/A N/A 0.013

ROOSK TRIB* 1269.5 09ROOS00134I 116.4 Circular

x3/

Irregular

1.40, 1.57 N/A, 3.03 N/A 0.013



ROOSK TRIB 1517.8 09ROOS00110I 11.4 Irregular 1.49 3 N/A 0.013

ROOSK TRIB* 1652.0 09ROOS00096I 510.0 Irregular 1.89 2.93 N/A 0.013

ROOSK TRIB 2334.5 09ROOS00029I 18.2 Arch 1.72 3.19 1 0.025


IBE0600Rp0016 4.18-53 F03

ROOSK TRIB 2408.0 09ROOS00021 2.0 Arch x2 1.51, 1.77 1.55, 1.47 0.79, 1.37 0.025


ROOSK TRIB 2427.0 09ROOS00019I 16.1 Arch 1.48 3.07 0.77 0.025



MILL RACE F TRIB 115.0 09MILF00102D 6.9 Arch 1.03 0.85 0.76 0.023

MILL RACE F TRIB 128.0 09MILF00101D 5.5 Irregular 2.97 4.6 N/A 0.013

MILL RACE F TRIB 856.0 09MILF00030D 6.3 Irregular 2.85 16.2 N/A 0.020

BALLYBRACK/ROESTOWN

TRIB

2994.9 09ROES00366D 9.2 Irregular

x2

0.93, 1.18 0.51, 0.54 N/A 0.025

BALLYBRACK/ROESTOWN

TRIB

3829.0 09ROES00281I 4.8 Irregular 1.81 1.16 0.020

BALLYBRACK/ROESTOWN

TRIB*

3871.1 09ROES00276I 262.4 Circular 1.15-0.9 N/A N/A 0.013

BALLYBRACK/ROESTOWN

TRIB

4198.7 09ROES00244I 6.7 Circular 1.2 N/A N/A 0.013

BALLYBRACK/ROESTOWN

TRIB

4355.4 09ROES00228D 9.6 Circular 1 N/A N/A 0.023

BALLYBRACK/ROESTOWN

TRIB

4882.2 09ROES00174I 49.5 Arch 2.42 3.55 0.76 0.019

BALLYBRACK/ROESTOWN

TRIB

6433.2 09ROES00019D 6.7 Arch 1.3 3.12 0.76 0.023

BALLYBRACK/ROESTOWN

TRIB

6497.2 09ROES00012D 6.7 Arch x3 4.3, 5.3, 6.4 9.3, 4.7, 4.7 1.7, 3.4, 4.4 0.025

LYREEN RIVER 70.5 09LYRE00425I 25.3 Arch 2.52 3.53 0.95 0.019


IBE0600Rp0016 4.18-54 F03



LYREEN RIVER 1177.5 09LYRE00314D 7.5 Irregular 2.06 6.06 N/A 0.025

LYREEN RIVER 1204.1 09LYRE00314I 28.2 Irregular 1.68 2.02 N/A 0.025

LYREEN RIVER 1650.4 09LYRE00266D

edit

16.5 Arch x2 1.84 (x2) 2.24, 2.58 1.05, 0.98 0.025

LYREEN RIVER 1956.0 09LYRE00237D

edit

17.9 Irregular 1.93 6.63 N/A 0.020

LYREEN RIVER 2452.6 09LYRE00190I 29.6 Irregular

x2

2.31 0.97, 2.38 N/A 0.015



LYREEN RIVER* 2778.5 09LYRE00153I 126.1 Circular/

Irregular

1.00, 1.16 N/A, 2.1 N/A 0.013

LYREEN RIVER 3062.7 09LYRE00126D 12.7 Arch x3 2.53, 3.04,

2.62

2.77, 3.38,

2.73

1.53, 1.74,

1.46

0.020

LYREEN RIVER 3994.0 09LYRE00033D 4.0 Arch 2.7 5.44 1.73 0.023

MILL RACE G TRIB 2.0 09MILG00005 0.5 Arch x2 0.50, 0.35 2.01, 1.81 0.18, 0.00 0.013

MILL RACE G TRIB 34.6 09MILG00002D 3.5 Irregular 0.75 2.36 N/A 0.013

RYE WATER 8859.7 09RYEW01042 1.0 Irregular 1.17 4.06 N/A 0.013

RYE WATER 9185.6 09RYEW01011D 3.6 Irregular 1.38 7.47 N/A 0.020

RYE WATER 9397.8 09RYEW00990D 8.0 Arch 3.64 3.36 2.12 0.020

RYE WATER 11408.8 09RYEW00788D 11.5 Arch x3 4.1, 4.6, 4.0 3.0 (x2), 4.6 3.1 (x2), 3.0 0.025

RYE WATER 11956.5 09RYEW00733D 2.3 Irregular 2.37 17.8 N/A 0.020

RYE WATER 12061.2 09RYEW00723D 4.5 Arch x5 2.9, 3.4 (x2), 3.2, 4.0 (x2), 1.5, 2.1, 2.0 0.020


IBE0600Rp0016 4.18-55 F03

3.5, 3.0 4.9, 3.3 (x2), 1.9

RYE WATER 13349.6 09RYEW00595D 5.1 Arch x3 3.5 (x3) 6.5, 6.5, 6.6 2.1, 2.0, 1.8 0.023

RYE WATER 14445.0 09RYEW00479D 4.3 Arch x2 3.6, 4.0 9.1, 8.7 1.3, 1.6 0.025

RYE WATER 15181.1 09RYEW00405D 4.6 Arch x3 4.4 (x2), 4.7 5.5 (x2), 6.2 1.9, 1.8, 1.5 0.020

MOYCLARE TRIB 22.8 09MOYC00102I 5.7 Circular 0.9 N/A N/A 0.013

MOYCLARE TRIB 577.8 09MOYC00048D 8.8 Arch 1.61 1.97 0 0.023

MOYCLARE TRIB 706.9 09MOYC00035D 9.2 Arch 1.72 3.38 0.6 0.023

MOYCLARE TRIB 829.5 09MOYC00023I 6.0 Circular 0.9 N/A N/A 0.013

MOYGADDY TRIB 673.9 09MOYG00041D 7.4 Arch 3.38 2.9 2.23 0.060

MOYGADDY TRIB 1070.1 09MOYG00001D 3.5 Arch 1.4 2.86 0.9 0.020

Structure Details – Weirs

RIVER BRANCH CHAINAGE ID MANNING'S N TYPE

ROOSK TRIB 2492.7 09ROOS00011W 0.035 Broad Crested Weir

MILL RACE F TRIB 597.8 09MILF00054W 0.015 Broad Crested Weir

MILL RACE F TRIB 1023.5 09MILF00012W 0.030 Broad Crested Weir

LYREEN RIVER 3082.1 09LYRE00123W 0.035 Broad Crested Weir

LYREEN RIVER 3903.0 09LYRE00041W 0.011 Broad Crested Weir

MILL RACE G TRIB 6.0 09MILG00005W 0.015 Broad Crested Weir

MILL RACE K TRIB 1.0 09MILK00001W 0.015 Broad Crested Weir

RYE WATER 9491.6 09RYEW00978W 0.011 Broad Crested Weir

RYE WATER 12997.8 09RYEW00628W 0.015 Broad Crested Weir

MOYGADDY TRIB 106.0 09MOYG00097W 0.015 Broad Crested Weir

MOYGADDY TRIB 1075.0 09MOYG00000W 0.015 Broad Crested Weir

* Denotes structures incorporated as closed cross-sections only (and are therefore not included in the Network file).


IBE0600Rp0016 4.18-56 F03

** Structure ID Key:

D - Bridge Upstream Face

E - Bridge Downstream Face

I - Culvert Upstream Face

J - Culvert Downstream Face

W - Weir Crest

NB: All other weirs in the Network file are overtopping weirs which form part of a composite structure with the culvert/bridge at the corresponding chainage.


IBE0600Rp0016 4.18-57 F03

APPENDIX A.2

Long section plots

Figure 4.18.52: Rye Water 1% AEP design run

Bridge 09RYEW00990D - Ch. 9397

Weir 09RYEW00628W - Ch. 12997

Lake at Carton Demesne

Moyclare confluence

Moygaddy confluence

Lyreen River confluence

RB

LB

Peak WL


IBE0600Rp0016 4.18-58 F03

Figure 4.18.53: Lyreen River 1% AEP design run

Inverted siphon culvert

09LYRE00314I - Ch. 1204

Ballybrack/ Roestown confluence

Gauging station 09049 - Ch. 3903

Mill Race F confluence

Mill Race K confluence

Mill Race G confluence

Mill Race F confluence

Roosk confluence

Crewhill confluence


IBE0600Rp0016 4.18-59 F03

APPENDIX A.3

Flow tables

IBE0600 EAST CFRAM STUDY RPS

PEAK WATER FLOWS

AFA Name MAYNOOTH

Model Code HA09_MAYN4

Status DRAFT FINAL

Date extracted from model 14/10/2014

Peak Water Flows

River Name & Chainage AEP Check Flow (m3/s) Model Flow

(m3/s) Diff (%)

BALLYBRACK/ROESTOWN TRIB 6234.39 50% 2.49 2.63 5.62

09_1464_1_RPS 10% 4.48 3.93 -12.23

1% 8.27 6.88 -16.84

0.1% 14.71 10.47 -28.82

ROOSK TRIB 2563.77 50% 2.83 3.06 8.27

09_1839_12_RPS 10% 5.08 5.51 8.37

1% 9.37 10.12 7.99

0.1% 16.66 19.23 15.41

CREWHILL TRIB 1811.14 50% 0.58 0.56 -2.76

09_1444_4 10% 1.05 1.00 -5.14

1% 1.94 1.86 -4.33

0.1% 3.46 3.37 -2.60

LYREEN RIVER 1802 50% 10.49 9.89 -5.68

09_1464_2_RPS 10% 17.68 15.92 -9.94

1% 30.33 31.64 4.32

0.1% 50.18 46.05 -8.23

LYREEN RIVER 2944.42 50% 10.92 10.10 -7.52

09_1464_5_RPS 10% 18.42 16.17 -12.20

1% 31.59 30.44 -3.66

0.1% 52.27 48.65 -6.92

LYREEN RIVER 3916.67 50% 12.40 11.53 -6.98

09049_RPS 10% 19.99 18.13 -9.29

1% 32.88 27.47 -16.46

0.1% 52.37 42.60 -18.66

LYREEN RIVER 4178.51 50% 12.29 11.57 -5.90

09_611_3_RPS 10% 19.81 18.39 -7.18

1% 32.60 31.99 -1.87

0.1% 51.92 52.82 -1.74

RYE WATER 13562.9 50% 29.78 26.48 -11.08

09_1260_4_RPS 10% 43.56 41.28 -5.24


IBE0600Rp0016 4.18-60 F03

1% 65.93 64.94 -1.50

0.1% 96.90 105.46 8.83

MOYCLARE TRIB 889.708 50% 2.51 2.40 -4.38

09_468_3 10% 4.51 4.36 -3.37

1% 8.34 8.06 -3.33

0.1% 14.87 14.67 -1.34

MOYGADDY TRIB 1039 50% 4.31 4.39 1.90

09_1060_3 10% 7.77 7.93 2.11

1% 14.41 14.64 1.58

0.1% 25.79 26.09 1.17

The table above provides details of the flow in the model at every HEP intermediate check point,

modelled tributary and gauging station. These flows have been compared with the hydrology flow

estimation and a percentage difference provided.

There are a number of complex hydraulic effects within this model which made the process of

anchoring the model flows to the hydrological estimates difficult. In order to better understand these

processes and achieve better overall correlation, an additional model run comprising the 50% AEP

design flows was undertaken and the results reported here. The estimated and modelled flows at

every HEP were found to correlate well during the 50% AEP design run, indicating that the model is

well anchored to low-flow conditions.

The estimated and modelled flows at the downstream ends of the Crewhill, Moyclare, Moygaddy and

Lyreen watercourses all correlate well for all model design runs.

The table shows that the estimated and modelled flows at the downstream end of the

Ballybrack/Roestown tributary correlate well during the 50% AEP design run, however during the 10%

AEP design run the modelled flow is around 12% lower than the hydrological estimate. The difference

between the estimated and modelled flows continues to increase as the design flow increases, with

the difference around 29% during the 0.1% AEP design run. The railway/ canal inverted siphon culvert

09LYRE00314I at chainage 1204 on the Lyreen River becomes surcharged during design runs of 10%

AEP or greater and causes severe out-of-bank flooding and ponding upstream of the culvert inlet as

shown in Figure 4.18.45. This ponding effect backs up flow in the Ballybrack/Roestown tributary,

resulting in modelled flows which are lower than the hydrological estimates. Hydraulic modelling can

represent this complex hydraulic effect better than hydrological estimation, so these differences in

estimated and modelled flows are considered to be acceptable, especially considering that this area

has been known to flood historically. Further confirmation for this conclusion is achieved as there is

good correlation during the 50% AEP design run, where the railway/ canal siphon culvert is not

surcharged and the ponding effect does not influence the modelled flows.

The railway/ canal inverted siphon culvert 09LYRE00314I also has a large impact on the HEPs on the

Lyreen River. The first intermediate HEP on the Lyreen River (09_1464_2_RPS) is located

approximately 600m downstream of the railway/ canal culvert and shows good correlation between the

estimated and modelled flows during 50% AEP and 1% AEP design runs, however the modelled flow

is approximately 10% and 8% lower than the hydrological estimates during the 10% AEP and 0.1%


IBE0600Rp0016 4.18-61 F03

AEP design runs respectively. Good correlation is shown during the 50% AEP design run as culvert

09LYRE00314I is not surcharged during this scenario and has sufficient capacity to convey the design

flow. During the 10% AEP design run this culvert becomes surcharged and causes flow to back up

upstream, resulting in a modelled flow lower than the hydrological estimate. During the 1% AEP

design run, flood water overtops the railway and canal, equalizing pressure in the inverted siphon and

improving conveyance. For this reason, the estimated and modelled flows correlate well during the 1%

AEP design run. This hydraulic effect also occurs during the 0.1% AEP design run, however flow takes

an alternative path along the canal during this scenario, hence resulting in a modelled flow lower than

the hydrological estimate. This alternative flow path is shown in Figure 4.18.45.

The next intermediate HEP on the Lyreen River (09_1464_5_RPS) is influenced by the same

hydraulic effects as 09_1464_2_RPS and correlation between estimated and design flows for each

design run follows the same pattern except that good correlation is displayed during the 0.1% AEP

design run at this point. This is because the flow that was diverted along the alternative route along the

canal (as shown in Figure 4.18.45) rejoins Mill Race F upstream of this HEP.

HEPs 09049_RPS is located at Maynooth gauging station. Good correlation is shown during the 50%

AEP and 10% AEP design runs, and the modelled flow is 16% and 19% greater than the estimated

flow during the 1% AEP and 0.1% AEP design runs respectively. Overall the modelled flow was found

to increase relative to the estimated flow for more extreme design runs at this point. This is because

the growth curve behaviour of the Lyreen catchment in the hydraulic model was found to be steeper

than the hydrological estimates. It is considered that the hydraulic model is better able to simulate the

complex behaviour of this catchment system as it is influenced by hydraulic features such as the

railway/ canal inverted siphon culvert, so this was deemed to be acceptable.

This growth curve behaviour was found to have a knock-on effect at HEP 09_1260_4_RPS on the Rye

Water at the downstream extent of the model. The model flow was found to be approximately 11%

below the estimated flow during the 50% AEP design run and approximately 9% greater than the

estimated flow during the 0.1% AEP design run. The modelled flows were generally found to increase

relative to the estimated flows for more extreme design runs due to the growth curve behaviour of the

Lyreen catchment being steeper in the hydraulic model than the hydrological estimates, and as

reported previously this was deemed to be acceptable as the hydraulic model can simulate this affect

better than hydrological estimation.

The estimated and modelled flow in the Roosk tributary correlate well during all design runs except

0.1% AEP where the modelled flow is approximately 15% greater than the hydrological estimate. Flow

from the Lyreen River spills onto the M4 motorway and joins the Roosk tributary during the 0.1% AEP

design, so this difference was considered to be reasonable.


IBE0600Rp0016 4.18-62 F03

APPENDIX A.4

MIKE FLOOD MIKE 21 MIKE 21 RESULTS

HA09_MAYN4_MF_DES_8_Q10 HA09_MAYN4_M21_DES_8_Q10 HA09_MAYN4_HD_DES_8_Q10

HA09_MAYN4_MF_DES_8_Q100 HA09_MAYN4_M21_DES_8_Q100 HA09_MAYN4_HD_DES_8_Q100

HA09_MAYN4_MF_DES_8_Q1000 HA09_MAYN4_M21_DES_8_Q1000 HA09_MAYN4_HD_DES_8_Q1000 HA09_MAYN4_MESH_2 HA09_MAYN4_MESH_FPR

MIKE 11 ‐ SIM FILE & RESULTS FILE MIKE 11 ‐ NETWORK FILE MIKE 11 ‐ CROSS‐SECTION FILE MIKE 11 ‐ BOUNDARY FILE

HA09_MAYN4_M11_DES_8_Q10 HA09_MAYN4_NWK_DES_8 HA09_MAYN4_XNS_DES_8 HA09_MAYN4_BND_DES_6_Q10

HA09_MAYN4_M11_DES_8_Q100 HA09_MAYN4_BND_DES_6_Q100

HA09_MAYN4_M11_DES_8_Q1000 HA09_MAYN4_BND_DES_6_Q1000

MIKE 11 ‐ DFS0 FILE MIKE 11 ‐ HD FILE & RESULTS FILE

HA09_MAYN4_DFS0_Q10 HA09_MAYN4_HD_DES_8_Q10

HA09_MAYN4_DFS0_Q100 HA09_MAYN4_HD_DES_8_Q100 HA09_MAYN4_DFS0_Q1000 HA09_MAYN4_HD_DES_8_Q1000


IBE0600Rp0016 4.18-63 F03

GIS Deliverables - Hazard

Flood Extent Files (Shapefiles) Flood Depth Files (Raster) Water Level and Flows (Shapefiles) Fluvial Fluvial Fluvial E28EXFCD100F0 E28DPFCD100F0 E28NDFCDF0 E28EXFCD010F0 E28DPFCD010F0 E28EXFCD001F0 E28DPFCD001F0

Flood Zone Files (Shapefiles) Flood Velocity Files (Raster) Flood Defence Files (Shapefiles) E28ZNA_FCDF0 E28VLFCD100F0 Defence Failure Extent E28ZNB_FCDF0 E28VLFCD010F0 E28FEFCD010F0 E28VLFCD001F0

GIS Deliverables - Risk

Specific Risk - Inhabitants (Raster) General Risk - Economic (Shapefiles) General Risk-Environmental (Shapefiles) Fluvial E28RIFCD100F0 E28RIFCD010F0 E28RIFCD001F0

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