interpretive flood report reva final

Document No. M-BAC-000000-CG00-RPT-000004 Rev 00A of 40 Interpretive Flood Report

Printed: 25-Jan-15

© 2013 High Commission for the Development of ArRiyadh

Electronic documents once printed, are uncontrolled and may become out-dated. Refer to Aconex for current revision.

Table of Contents 1 INTRODUCTION ............................................................................................................................................3

1.1 BACKGROUND ............................................................................................................................................................................3 1.2 PURPOSE .....................................................................................................................................................................................3 1.3 REPORT AND RESOURCES.......................................................................................................................................................3 1.4 HOW TO USE THIS REPORT ...................................................................................................................................................4

2 EMPLOYER REQUIREMENTS (ER)............................................................................................................4

3 CLIMATE CHANGE ........................................................................................................................................5

4 FREEBOARD...................................................................................................................................................5 4.1 RISK-BASED FREEBOARD ALLOCATION..............................................................................................................................5

5 FLOOD DESIGN STANDARDS ADOPTED BY BACS ................................................................................7

6 FLOOD MAPS..................................................................................................................................................7 6.1 HARD COPIES (*.PDF FORMAT ...........................................................................................................................................7 6.2 SOFT COPIES (*.TIFF FORMAT ...........................................................................................................................................7 6.3 USING THE GIS MODEL OUTPUT FILES ..............................................................................................................................8

7 RECOMMENDED DESIGN FLOOD LEVELS............................................................................................ 10

8 DESIGN CENTRE RESPONSIBILITIES .................................................................................................... 11

9 FLOOD ASSESSMENT ASSUMPTIONS AND LIMITATIONS ............................................................... 11


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1 Introduction

1.1 Background BACS have appointed consultants Buro Happold (BH) to carry out an assessment of the flood risk to key Riyadh Metro Project (RMP) infrastructure within Package 1, resulting from rainfall-runoff and overland flow. As per the Employer Requirements, the assessment considers the 1 in 100 year Average Recurrence Interval (ARI) flood event, including an allowance for climate change (hereafter referred to as the ‘design flood event’). The assessment concluded that a number of the RMP items are at risk of flooding from overland flow in the design flood event. In each case, the estimated depths of flooding and peak velocities have been provided such that the Design Centres can consider flood mitigation measures to protect RMP infrastructure from this risk.

1.2 Purpose

The purpose of this interpretive report is to communicate the following information to the respective design teams in order to inform flood protection and mitigation designs:

available flood risk information available tools Design Centres can use to inform their designs recommended freeboard allowances and resulting design flood levels (derived at specific

locations only).

1.3 Report and Resources

The final BH report, entitled ‘Riyadh Metro Package 1 - Assessment of Flood Risk, Final Report, RevB’ dated 27-Nov-2015 is available on ACONEX. Appendices B & C, flood maps and velocity maps respectively, were uploaded as separate documents due to file size restrictions. Soft-copy GIS-compatible model output files are also available for flood depths, velocities and hazards, and are available on ACONEX in a zipped format. Table 1 Available Information

Document ACONEX Number

Final Flood Assessment Report, RevB (*.pdf) M-BBH-000000-CG00-RPT-000001

Appendix B – Flood Depth Maps (.*zip) M-BBH-000000-CG00-RPT-000002

Appendix C – Velocity Maps (.*zip) M-BBH-000000-CG00-RPT-000003

GIS Model Output Files – Flood Depths (.*zip) M-BBH-000000-CG00-RPT-000004

GIS Model Output Files – Flow Velocities (.*zip) M-BBH-000000-CG00-RPT-000005

GIS Model Output Files – Flood Hazards (.*zip) M-BBH-000000-CG00-RPT-000006

The BH report provides context regarding flood risk in Riyadh and known flood mechanisms, information on the methodology adopted for hydrologic and hydraulic modelling and the modelling assumptions and limitations.


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1.4 How to Use This Report

This interpretive report is issued as a guide to Design Centres on how to interpret and use the available flood risk information to inform their respective designs. Whilst the BH report contains generic information and recommendations, this interpretative report aims to provide more specific guidance to Design Centres. When studying and interpreting the BH report, it is important to note that:

the BH report recommends a blanket freeboard allowance of 500mm. This interpretive report recommends location-specific freeboard allowances, as reported in Table 6; and

the BH report estimates flood levels (i.e. elevations) at specific locations. However, because of a datum difference between the flood study’s surface model and the project topographical data the flood levels reported by BH in their report cannot be used for design purposes. Instead, the approach outlined in this report should be used to derive design flood elevations.

2 Employer Requirements (ER)

The technical specifications for flood protection and stormwater drainage for RMP are provided in the RMP Tender Documentation - Volume 2: Employer’s Requirements. Sections of the requirements relevant to flood protection and drainage design are provided in Table 2. Table 2 Employers Requirements Relevant to Flood Protection and Stormwater Drainage

Relevant ER Volume

Relevant ER Section Requirements

Volume 2.2, Part 3 - Environmental Specification

Section 2.1.4 Rainfall

Rainfall and storm waters: the metro Lines shall be able to evacuate the water to the city storm water network in sufficient time not to disturb operation.

The metro may be able to run even when parts of the track are over flooded with a maximum 10cm height of water along 200m

All underground parts shall be ensured that no flooding will disturb the functioning of any metro System Components.

Section 2.1.5 Flood Zones

The system shall be capable of surviving flooding (100-year) with minimal damage to structure and equipment.

Equipment and facility elements that can be damaged by flooding shall be protected or installed above the flood plain elevation.

Section 5.2.5 Station Access

The Contractor shall carry out the design of the interface with the street area in close co-operation with the public authorities, and shall consider all constraints due to climatic conditions, risks of flooding, etc…

Volume 2.3 WPS 2.01 Civil Works & Infrastructure Design Requirements

Section 3.3.3 Basis of Design

For the design of the project drainage system, a storm recurrence period of 10 years shall be considered for all drainage elements except for the flood protection elements which shall be designed for a storm recurrence period of 100 years.


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3 Climate Change

The ER doesn’t specifically address climate change; however, the contract (Exhibit D) stipulates a ‘specified design life of 100 years for all permanent civil engineering structures’ and that ‘the design subcontractor shall carefully identify the requirements to the design and construction that will secure the stated service life’ (Section 5.3.1, Page 18). As such, an allowance for climate change over the life of the RMP system was taken into account to ensure that infrastructure with a present day 1 in 100yr ARI flood protection standard will have that same standard towards the end of its design life. The assessment of the effects of climate change has been informed by the findings of Al Zawad1, which estimates that for the range of emissions scenarios, the impacts of climate change on rainfall is likely to be between a -7% and +40% change in rainfall intensity. A median value of +20% has been adopted which is in line with the recommendations of the Arriyadh Stormwater Masterplan Review, as agreed with the Arriyadh Development Agency (ADA).

4 Freeboard

Freeboard is often defined as the difference between the design flood level and the ultimate flood protection level. It’s an additional level allowance which is added to an estimated design flood level to accommodate uncertainty. Freeboard is an industry recognised design allowance to account for the inherent uncertainties associated with flood estimation and physical imponderables such as post-construction settlement or wave action. Appropriate freeboard allowances for design purposes were selected by BACS, as reported in Table 5 of this report. These freeboard recommendations are underpinned by a risk-based assessment, taking into account the consequences of flooding on the protected asset, as well as the degree of uncertainty involved in the flood estimation process. The risk-based assessment has been issued to RMTC for endorsement (Aconex Document No: M-BAC-000000-CG00-RPT-000003).

4.1 Risk-based Freeboard Allocation

BACS have adopted a risk-based approach in setting freeboard allowances for the various RMP design components, by considering the following factors:

flood source flood depth, velocity, and resulting flood hazard (flood hazard is a metric for determining the

level of danger to pedestrians and vehicles based on a combination of flood depth and velocity)

potential consequences of flooding and intended use of RMP design component (e.g. flooding of a station versus flooding of a park-and-ride)

existing stormwater drainage provisions in the area nature of the surrounding land and flow paths (e.g. where land slopes away from a station a

minimal freeboard will be required)

1 Al Zawad, F. M., 2008, Impacts of Climate Change on Water Resources in Saudi Arabia, 3rd International Conference on Water Resources and Arid Environments and the 1st Arab Water Forum


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An estimated flood hazard was calculated for each RMP Package 1 design component using the ‘Flood Risk to People Best Practice Guide’2. The equation for calculating flood hazard is: Hazard Rating = depth x (velocity + 0.5) + debris factor The debris factor considers the ability of the flow to mobilise debris that may pose a risk to people or vehicles. Table 3 provides a summary of resultant hazard classifications, whilst Table 4 presents hazard rating values for combinations of depth (m) and velocity (m/s). Table 3 Flood Hazard Rating

Hazard Rating Flood Hazard Description

Less than 0.75 Low Caution

0.75 – 1.25 Moderate Danger for some pedestrians (i.e. children and the elderly)

1.25 – 2.50 Significant Danger for most pedestrians and some vehicles

More than 2.50 Extreme Danger for all pedestrians and vehicles

Table 4 Hazard Rating Matrix

FLOOD HAZARD

Velocity (m/s)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Floo

d D

epth

(m)

0.1 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 0.2 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 0.3 1.15 1.30 1.45 1.60 1.75 1.90 2.05 2.20 2.35 2.50 2.65 0.4 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 0.5 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 0.6 1.30 1.60 1.90 2.20 2.50 2.80 3.10 3.40 3.70 4.00 4.30 0.7 1.35 1.70 2.05 2.40 2.75 3.10 3.45 3.80 4.15 4.50 4.85 0.8 1.40 1.80 2.20 2.60 3.00 3.40 3.80 4.20 4.60 5.00 5.40 0.9 1.45 1.90 2.35 2.80 3.25 3.70 4.15 4.60 5.05 5.50 5.95 1.0 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 1.1 1.55 2.10 2.65 3.20 3.75 4.30 4.85 5.40 5.95 6.50 7.05 1.2 1.60 2.20 2.80 3.40 4.00 4.60 5.20 5.80 6.40 7.00 7.60 1.3 1.65 2.30 2.95 3.60 4.25 4.90 5.55 6.20 6.85 7.50 8.15 1.4 1.70 2.40 3.10 3.80 4.50 5.20 5.90 6.60 7.30 8.00 8.70 1.5 1.75 2.50 3.25 4.00 4.75 5.50 6.25 7.00 7.75 8.50 9.25 1.6 1.80 2.60 3.40 4.20 5.00 5.80 6.60 7.40 8.20 9.00 9.80 1.7 1.85 2.70 3.55 4.40 5.25 6.10 6.95 7.80 8.65 9.50 10.35 1.8 1.90 2.80 3.70 4.60 5.50 6.40 7.30 8.20 9.10 10.00 10.90 1.9 1.95 2.90 3.85 4.80 5.75 6.70 7.65 8.60 9.55 10.50 11.45 2.0 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00

2 DEFRA/Environment Agency, 2006, Flood Risks to People Phase 2 FD2321/TR2


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The following risk-based freeboard allowances are recommended by BACS: Table 5 Risk-based Freeboard Allowances

Modelled Flood Depth (1:100yr ARI + 20% climate change

allowance) Standard Freeboard

(mm) Additional Freeboard*

(mm)

0mm - 100mm 50 50

100mm - 200mm 100 100

200mm - 500mm 200 100

500mm - 1m 250 150

>1m 350 150

*Additional freeboard allowances are required in areas of significant/extreme flood hazard areas, or where flood impacts on critical infrastructure are deemed significant.

5 Flood Design Standards Adopted by BACS

The following basis of design was adopted for Package 1 in relation to flood protection:

Flood protection: 1:100yr ARI + 20% climate change + freeboard (refer to Table 5). Stormwater drainage design: 1:10yr ARI.

6 Flood Maps

6.1 Hard Copies (*.PDF format)

Flood maps, showing the indicative flood depth in the vicinity of stations, portals, access shafts, depots and TBM launch locations were produced and are presented in Appendix B of the flood report. Flood velocity, also indicating the direction of flow, is presented in Appendix C of the flood report. Hard copies of the flood maps can be downloaded from ACONEX (refer to Table 1).

6.2 Soft Copies (*.TIFF format)

Soft copy, GIS-compatible model output files that represent flood depth, velocity and hazard are also available from ACONEX (refer to Table 1). Seven flood models were developed to represent the wider Riyadh area. Model 1GHJ however is currently being reviewed, and outputs from this model will be made available as part of Revision B of this report, anticipated to be issued during w/e 30th Jan 2015. As a result, six separate GIS model outputs files are currently available, covering the catchments overlapping with Lines 1 and 2, as shown on Figure 1.


Printed: 25-Jan-15



Figure 1 Flood Model Extents

Note: Models C15 and 2F2 overlap in coverage. Please refer to Section 6.3for guidance on which GIS output file to use for assessment purposes.

6.3 Using the GIS Model Output Files

The GIS model output files provide the flood modelling outputs. The format is a raster dataset with a resolution (grid cell size) of 5x5m for 6 of the models and a 15x15m resolution for one of the models (C15). As explained in Section 6.2 a 15m grid had to be adopted for Model C15 due to the size of its associated catchment, to limit model run times.

Each 5x5m (or 15x15m in the case of Model C15) cell represents a uniform result i.e. regardless of where one clicks within a cell it will produce the same flood result (depth, velocity or hazard).

The GIS model output files are georeferenced and as such can be imported directly into most GIS software applications such as ArcGIS, as well as some CAD software packages. By overlaying these layers onto project design information, associated flood risk information can be extracted at any point of interest. When first imported the TIFF files will display in monochrome, and the GIS/CAD operator must set the layer properties (e.g. symbology, colour ramp) manually to suit.

Model 1F8

Model 2A1

Model 1A3

Model 1GHJ Model L1S

Model C15

Model 2F2


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Figure 2 Typical Flood Depth Map Extract, showing 5x5 m Grid

Modelled flood level information (i.e. water surface elevation) is not currently available. Design flood levels, as reported in Table 6 were derived by adding the modelled flood depth at a specific location to the topographical spot elevation at that location, including an allowance for freeboard. The indicative nature of flood modelling must be borne in mind when Design Centres interpret the results, and a conservative approach should be adopted where possible. Freeboard allowances must be incorporated in the any flood protection design to accommodate uncertainty. Model Overlap - C15 and 2F2 As noted in Section 6.2 Models C15 and 2F2 overlap in their geographic coverage. C15 is a large catchment, for which a larger resolution (grid cell size) of 15x15m was adopted to make model run times more manageable. The 2F2 area was run with a finer resolution (5m grid) in order to gain greater clarity on the overland flow route which is known to come through the Ghirnatah and Ishniliyah neighbourhoods via Al Imam Abdullah Ibn Saud Ibn Abdulaziz Road.

Although Model C15 identifies these flow paths, it was considered that the additional detail provided by Model 2F2 would be of use in identifying the risk to Stations 2F1 and 2F2 from this flow path.

As such, for the stations covered by Model 2F2, the GIS model output files for Model 2F2 should be used for assessment/design purposes because it provides greater detail on the flood mechanisms for this area.

Each of these cells represents a 5x5 m area (or in the case of Model C15 a 15x15m area)


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7 Recommended Design Flood Levels

Based on the approach outlined in Section 6.3, design flood levels were derived at a specific spot location for each station, shaft, portal, depot, park-and-ride, TBM launch shaft and at-grade location within depressed underpasses. Recommended design flood levels at these specific locations are presented in Table 6. It is important to note that the design flood levels provided in Table 6 are only applicable to the spot location shown, and it is the Design Centres’ responsibility to use the GIS model output files provided to ensure that all critical points of access are adequately protected against the design flood event (incl. an allowance for freeboard). Recommended freeboard allowances as provided in Table 6 are applicable to the whole facility (station, depot etc.) it refers to. Topographical Spot Levels The nature of the spot level is provided in Table 6, using the following abbreviations:

AS: ‘Road Asphalt’ AS+CS: ‘Bottom of Road Kerb Stone’ AS+JB: ‘Bottom of Jersey Barrier, on Asphalt Level’ MY: ‘Road Marking Lane Line Yellow’ NGL: ‘Natural Ground Level’ Interpreting the Flood Depth Maps in Table 6 The following legend should be used to interpret the flood map extracts shown in the last column of Table 6, and refers to the indicative depth of flooding.

Figure 3 Legend for interpreting the flood depths shown in Table 6


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8 Design Centre Responsibilities

The Design Centres are responsible for the final designs, and that appropriate and adequate flood protection measures are incorporated into the final designs. The recommended design flood levels provided in Table 6 is a guide only, and Design Centres should use all the tools available to ensure that critical and vulnerable infrastructure is adequately raised or protected against flooding. Given the varying nature of the terrain in many places, one single recommended design flood level (as provided in Table 6) may not be adequate for large facilities such as depots. As such the GIS model output files should be superimposed onto the relevant design, and design flood levels estimated at all locations that have the potential to allow flood water ingress. Freeboard allowances, in accordance with Table 6 should be applied to account for uncertainty.

9 Flood Assessment Assumptions and Limitations

The effects of any local drainage infrastructure have been ignored in the flood modelling.

Where underpasses are concerned, the modelling has been carried out on the assumption that the installed pumping infrastructure serving the underpass does not contribute to the evacuation of water entering the underpasses.

The metro stations, access shafts and TBM launch pits were all assessed as being

designed to exclude flood water. In this manner, it is possible to determine from the model the flood level against which these items should be designed.


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Table 6 Recommended Flood Design Levels

Location (Spot Level Location#)

Estimated Flood Depth*

(m)

Estimated Existing

Ground Level (m AEA)

Estimated Flood Level

A (m AEA)

Recommended Freeboard B

(m) Recommended Design Level

A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard

(Highest Category Stated at General

Location)

Notes

Flood depth, ground level and recommended design flood level are provided for a specific spot location, represented by a red dot on flood map extracts below. Designers should overlay the GIS modelling outputs onto their designs to approximate

flood depths at other locations of interest – please refer to Sections 6 to 8) Standard Additional Total

STATIONS

1Y1

(NGL, west of track)

0.35 652.98 653.33 0.2 0 0.2 653.5 0.03 Moderate

The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station. A park-and-ride facility is being proposed at 1Y1 which may be subject to flood risk, subject to its location and nature.

1Z1

(AS+CS, centre of

road, intersection)

0.40 646.72 647.12 0.2 0.1 0.3 647.4 0.8 Significant

The general slope of the catchment at this location directs water towards the junction from the north along Olaya Street and from the east along Anas Ibn Malik Road. The central median on Anas Ibn Malik Road will prevent water draining to the road from the north from crossing the road until the water reaches the junction.

1A1

(NGL) <0.01 638.58 638.58 0.05 0.05 0.1 638.7 0.01 Low

The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station.


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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1A2

(MY, centre of road,

northbound lane)

<0.01 633.86 633.87 0.2 0.1 0.3 634.2 0.15 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains.

1B1

(AS+CS, centre of

road, northbound

lane)

<0.1 627.75 627.78 0.2 0.1 0.3 628.1 0.6 Low


1B2

(AS+CS, centre of

road, northbound

lane)

<0.01 634.91 634.91 0.2 0.1 0.3 635.2 0.2 Low



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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1B3

(NGL) 0.50 619.95 620.35 0.25 0.15 0.4 620.8 0.05 Significant

This flood hazard is unlikely to occur within the station site once the station has been raised, however, this risk will still occur in the vicinity of the site and should be taken into account when considering the movement of some vulnerable people around the roads adjacent to the station.

1B4

(AS+CS, centre of

road, intersection)

<0.1 628.66 628.67 0.2 0.1 0.3 629.0 0.16 Low


1C1

(AS+CS, centre of

road, northbound

lane)

<0.01 630.43 630.43 0.2 0.1 0.3 630.7 0.1 Low



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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1C2

(AS+CS, centre of

road, southbound

lane)

<0.01 616.13 616.14 0.2 0.1 0.3 616.4 0.11 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. Also, There are anecdotal reports of flooding at this intersection, with ponding at the west side of Olaya Street affecting local businesses and causing traffic disruption.

1C3

(AC+CS, centre of

road, southbound

lane)

<0.01 612.57 612.57 0.2 0.1 0.3 612.9 0.25 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. There is a noticeable slope on Olaya Street from the north to the south, draining water towards the intersection.

1C4

(AS, centre of road,

southbound lane)

<0.1 603.90 603.96 0.2 0.1 0.3 604.3 0.37 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. The current stormwater database shows drainage along Prince Sultan Ibn Abdulaziz Rd draining to King Fahd Rd, although the BH site visit noted that a number of the gullies draining to this sewer were blocked with sediment. There are proposals to enlarge the culvert along Prince Sultan ibn Abdulaziz to provide a 125yr standard of protection.


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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1D2


southbound lane)

<0.01 611.78 611.78 0.2 0.1 0.3 612.1 0.07 Low


1D5


northbound lane)

<0.1 596.36 596.41 0.2 0.1 0.3 596.7 0.4 Low


1E2


southbound lane)

<0.1 589.50 589.52 0.2 0.1 0.3 589.8 0.5 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. There are currently no proposals to construct and new drainage infrastructure at the station location in the Arriyadh Stormwater Masterplan, although there are proposals to enlarge the Altabari Rd culvert 300m to the south-east of the station.


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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1F2


southbound lane)

<0.1 586.50 586.56 0.2 0.1 0.3 586.9 0.09 Low


1F4


southbound lane)

<0.1 584.70 584.74 0.2 0.1 0.3 585.0 0.04 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. The velocities around the station location range between 0.11m/s and 0.35m/s resulting in a low to significant flood hazard. The fast flowing water on King Saud Rd near to the station location may pose a risk to most pedestrians and some vehicles.

1F5


southbound) lane

<0.1 582.95 582.98 0.2 0.1 0.3 583.3 0.35 Low



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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1F7

(AS, parking lot, NE corner)

<0.01 580.73 580.73 0.2 0.1 0.3 581.0 0.03 Low


1F8

(AS+CS, side of road,

northbound lane)

0.70 578.37 579.07 0.25 0.15 0.4 579.5 0.7 Significant

Station 1F8 is located at the intersection of Al Batha and Al Ras Streets. The current stormwater database shows a box culvert on Al Batha Street. There are proposals to upgrade this culvert to provide a 1:25yr standard of protection. The velocities around the station location are in the order of 0.8m/s resulting in a significant flood hazard. The fast flowing water at the station location will pose a risk to most pedestrians and some vehicles.

1F9 Note: Flood Model 1GHJ is currently being revised which is likely to result in changes in flood levels at Station 1F9. Flood risk information for this location will be included in Revision B of this report, anticipated to be issued during w/e 30th Jan15.

1G1


westbound lane)

0.65 576.29 576.94 0.25 0.15 0.4 577.3 0.18 Significant

The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station. Flood risk and hazard is much increased within the underpass on Al Batha St as it passes underneath Al Amir Mohammed Ibn Abdul Rahman Rd, with the flood hazard significant.

1G2 Note: Flood Model 1GHJ is currently being revised which is likely to result in changes in flood levels at Station 1G2. Flood risk information for this location will be included in Revision B of this report, anticipated to be issued during w/e 30th Jan15.


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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1H2


westbound lane)

0.15 580.30 580.45 0.1 0 0.1 580.5 0.5 Low

A park-and-ride facility is being proposed at 1H2 which may be subject to flood risk, subject to its location and nature. The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station.

1J1


northbound lane)

<0.1 586.43 586.45 0.05 0 0.05 586.5 0.3 Low


1J2


northbound lane)

<0.1 584.71 584.78 0.05 0 0.05 584.8 0.4 Low

A park-and-ride facility is being proposed at 1J2 which may be subject to flood risk, subject to its location and nature. The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station.


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(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



2A1

(AS, centre of road, NE-bound lane)

<0.1 637.88 637.92 0.05 0 0.05 638.0 0.6 Low

The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station. To the SW of the station flood depths on King Abdullah Rd reach ~0.5m. If the track remains elevated at this location as currently shown in the design drawings, it is not considered that this will pose a risk.

2A2

(AS, centre of road, SW-bound lane)

<0.1 653.54 653.64 0.05 0 0.05 653.7 0.11 Moderate

A park-and-ride facility is being proposed at 2A2 which may be subject to flood risk, subject to its location and nature. The flood depths are unlikely to affect the station as the station is elevated, but there may be impacts on the ground level infrastructure such as electrical equipment. Flooding may also prevent access to and from the station.

2A3

(AS+CS, side of NE-bound lane, within underpass)

0.90 619.40 620.30 0.25 0.15 0.4 620.7 0.6 Significant

Flood depths in the vicinity of the station location at ground level are generally < 0.1m based on the local topography levels. For the underpass level at which the station and track are located, the depths of flooding are ~1m.This depth of water is close to impacting on the track level within the King Abdullah Rd underpass, and even if the metro construction detail showing a 1.1m high jersey barrier is sufficient to exclude the still water flood level, it will not provide a sufficient freeboard to achieve the design level.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



2B1


4.70 609.58 614.28 0.35 0.15 0.5 614.8 2.5 Extreme

Further, more detailed flood assessment work may be required for 2B1, which is located in a historic Wadi-valley, and affected by overland flow from the north. The effects of pumps and the drainage network were not considered in the flood assessment, potentially resulting in a conservative design flood level estimate. It is understood that the current design flood level is ~612.68m (~2m below the recommended design level).

2B2

(NGL) 0.50 619.95 620.35 0.25 0.15 0.4 620.8 0.05 Significant

This flood hazard is unlikely to occur within the station site once the station has been raised, however, this risk will still occur in the vicinity of the site and should be taken into account when considering the movement of some vulnerable people around the roads adjacent to the station.

2B4


<0.01 626.33 626.34 0.2 0.1 0.3 626.6 0.03 Low



Printed: 25-Jan-15





(m)

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Location)

Notes



2C1

(AS+JB, centre of

road within underpass, NE-bound

lane)

4.50 617.18 621.68 0.35 0.15 0.5 622.2 0.8 Extreme

The current drainage network shows existing drainage along King Abdullah Road, which discharge into the network on King Abdulaziz Rd. A further expansion to the network to the north of the station is proposed as part of the Arriyadh Stormwater Masterplan. It is anticipated that this will increase the storm flows being carried by the network in King Abdulaziz Rd. At street level the flood hazard may pose a danger to most pedestrians and some vehicles.

2C2


<0.01 630.77 630.78 0.05 0 0.05 630.8 0.02 Low

The current drainage network shows existing drainage in King Abdullah Rd at the station location. Enlargement of this culvert is proposed as part of the Arriyadh Stormwater Masterplan as well as a new line on Prince Nasser Bin Farhan Street.

2C3


0.20 659.96 660.16 0.1 0 0.1 660.3 0.05 Low



Printed: 25-Jan-15





(m)

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Notes



2C4


<0.1 653.11 653.13 0.05 0 0.05 653.2 0.14 Low

The current drainage network shows no existing drainage at the station location but there are networks currently in tendering to the north of the station location. No expansion to the network is proposed as part of the Arriyadh Stormwater Masterplan.

2D2

(AS+JB, centre of

road within underpass, SW-bound

lane)

3.87 609.57 613.44 0.35 0.15 0.5 613.9 0.3 Extreme

The current drainage network shows no existing drainage at the station location. A further expansion to the network is proposed to the north of King Abdullah Rd along the Eastern Ring Rd and Khalid Ibn Al Walid St as part of the Stormwater Masterplan. This will drain water towards Wadi Sulay. The estimated depth of water is likely to flood the station and the metro line, despite the presence of the jersey barriers.

2E1

(AS in

parking area south of main

road)

<0.1 608.15 608.24 0.2 0.1 0.3 608.5 0.3 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. An expansion to the drainage network is proposed along King Abdullah Rd and south along Ash Sheikh Hasan Ibn Hussain Ibn Ali Rd. This will receive water from 2D2 and drain towards Wadi Sulay. Estimated depth of water in the underpass is below the jersey barrier levels.


Printed: 25-Jan-15





(m)

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Location)

Notes



2E2

(AS+CS, centre of

road, SW-bound lane)

<0.1 596.89 596.95 0.2 0.1 0.3 597.2 0.4 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. An expansion to the drainage network is proposed along Salman Al Farsi Rd as part of the Arriyadh Stormwater Masterplan, although this is 300m to the SE of the station location.

2F1

(AS+JB, centre of


<0.1 588.76 588.78 0.05 0 0.05 588.8 <0.1 Low

There is ponding on land adjacent to King Abdullah Road to the north of the station, up to depths of ~1.9m (considered to be ‘extreme’ hazard) and therefore it is recommended that users of the station are not directed to the land to the north of the station

2F2

(NGL)

<0.1 585.16 585.17 0.2 0.1 0.3 585.5 <0.1 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. There is significant ponding observed to the north of the station up to depths of ~1.5m (categorised as ‘extreme’ hazard) although this does not appear to affect the station due to the difference in ground levels.


Printed: 25-Jan-15





(m)

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A (m AEA)



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Location)

Notes



2G1

(NGL) 0.30 577.97 578.27 0.2 0.1 0.3 578.6 0.2 Moderate

A park-and-ride facility is being proposed at 2G1 which may be subject to flood risk, subject to its location and nature.

ACCESS SHAFTS

1A2-1B1

(AS+CS, side of

northbound lane)

<0.01 631.26 631.28 0.2 0.1 0.3 631.6 0.2 Low


1B1-1B2

(AS+CS, centre of

road, northbound

lane)

0.05 631.64 631.69 0.2 0.1 0.3 632.0 0.5 Low



Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1B2-1B3

(AS, side of northbound

lane)

<0.1 628.36 628.38 0.2 0.1 0.3 628.7 0.25 Low


1B4-1C1


northbound lane)

<0.1 628.35 628.44 0.2 0.1 0.3 628.7 0.1 Low


1C1-1C2


northbound lane)

<0.01 622.38 622.39 0.2 0.1 0.3 622.7 0.3 Low



Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



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Estimated Flood

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Flood Hazard


Location)

Notes



1C2-1C3

(AS+CS, centre of

road, southbound

lane)

<0.01 615.42 615.42 0.2 0.1 0.3 615.7 0.2 Low


1C3-1C4

(AS+CS, centre of

road, northbound

lane)

<0.01 611.20 611.20 0.2 0.1 0.3 611.5 0.3 Low


1C4-1D2

(AS+CS, centre of

road, southbound

lane)

<0.1 603.47 603.49 0.2 0.1 0.3 603.8 0.2 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. To the NE of the access shafts there are areas of significant flood hazard. Evacuation from the shafts should not direct people towards this area.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

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Flood Hazard


Location)

Notes



1D2-1D5

(AS, centre of road, SE-bound lane)

0.2 602.95 603.13 0.2 0.1 0.3 603.4 0.3 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. The model shows that there are significant flood depths in the underpass north of the access shafts, with depths reaching up to 2.7m. Outside of the underpass where the shafts are located, expected flood depths are shallower.

1E2-1F2

(MY, centre of road, SE-bound lane)

<0.01 587.76 587.78 0.2 0.1 0.3 588.1 0.3 Low


1F4-1F5


southbound lane)

<0.1 584.14 584.23 0.2 0.1 0.3 584.5 0.35 Low



Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



1F5-1F7


northbound lane)

<0.1 581.33 581.43 0.2 0.1 0.3 581.7 0.6 Low


2B1-2B2

(AS+JB, centre of


<0.1 621.15 621.15 0.2 0.1 0.3 621.5 < 0.1 Low


2B2-2B4

(AS+JB, centre of


<0.1 628.97 629.00 0.2 0.1 0.3 629.3 < 0.1 Low



Printed: 25-Jan-15





(m)

Estimated Existing



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Location)

Notes



DEPOTS

L1 Primary Depot – South

(NG in low

spot on site)

0.79 580.52 581.31 0.25 0.15 0.4 581.7 0.11 Significant

Flood depths across the site range from 0.1m to 0.45m, with one area in the south-east experiencing depths of 0.88m. It is considered that re-profiling of the land levels will eliminate local ponding to these depths, although the potential effect of altering the flood and flow characteristics on third party land should be considered by the Design Centre. The ‘significant’ flood hazard only refers to the low spot, general the hazard across the site is ‘low’.

L1 Secondary

Depot – North

(NGL in northern

section of site)

0.96 657.26 658.22 0.25 0.15 0.4 658.6 0.6 Significant

The depot is located in the path of a significant overland flow route which drains the land to the north and NE of the depot, originating from flow collecting on King Abdulaziz Rd. Water flows overland until it reaches the interchange between Prince Salman Rd and King Fahd Rd. A secondary, smaller flow route enters the depot site from the east, and discharging into the major flow route from the north. Flood depths within the site vary significantly. Flood depths along the major flow route from the north are between 0.8m and 1.2m, whilst outside of this flow route the depths are generally <0.3m. If works are undertaken to raise the site in order to remove the risk associated with the flow route from the north, diversion of the overland flow route will be required, and the potential impacts on third parties will need to be assessed by the Design Centre. Along this flow route the peak flow rate is 17.75m3/s


Printed: 25-Jan-15





(m)

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Location)

Notes



Line 2 East Depot

(NGL

between raised tracks)

0.55 578.81 579.36 0.25 0.15 0.4 579.8 0.05 Significant

Part of the site is covered by construction waste that has been dumped on the open land, whilst part of the site is currently subdivided with constructed roads ~0.75m above existing land levels. The current flood risk to this location arises from two sources: flow along the historical bed of Wadi Sulay which passes through along the eastern edge of the site and overland flow from the urban areas to the west and NW. Please refer to page 52 of the BH report for more detailed information.

PORTALS

Portal 1A1

(AS+CS, centre of

road, northbound

lane)

<0.01 634.31 634.32 0.35 0.15 0.5 634.8 0.1 Low

Despite its low flood hazard a freeboard allowance higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being a tunnel portal; to cater for localised runoff or unexpected incidents such as burst water mains. The modelling shows the depths on Olaya Street at this location generally <0.1m. North of the portal location are a number of underpasses underneath the Northern Ring Road and its branch roads. The flood depths in these underpasses are up to 4.6m, which may flood the track and prevent operation of the metro. This needs to be taken into account during the finalisation of the vertical alignment of the metro tracks through this section of the city.


Printed: 25-Jan-15





(m)

Estimated Existing



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Estimated Flood

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Location)

Notes



Portal 1F8


southbound lane)

0.53 578.02 578.55 0.35 0.15 0.5 579.0 0.9 Significant

The track alignment shows the track passing along the route of the current median along Al Batha Street. The modelling shows the depths on Al Batha Street at this location between 0.5m and 0.6m.

Portal 2B1


4.70 609.58 614.28 0.35 0.15 0.5 614.8 2.5 Extreme

Further, more detailed flood assessment work may be required for the 2B1 location, which is located in a historic Wadi-valley, and affected by overland flow from the north. The effects of pumps and the drainage network were not considered in the flood assessment, potentially resulting in a conservative design flood level estimate. It is understood that the current design level is ~612.68m (~2m below the recommended design level).

Portal 2B4

(AS+JB, centre of road, NE-

bound lane)

<0.01 625.33 625.33 0.35 0.15 0.5 625.8 0.6 Moderate

To the east of the portal, the flood depth within the underpass is estimated at 4.9m. Providing that the track at this location is adequately protected then water will not be able to flow from Station 2C1 towards the portal and into the deep underground station. Track drainage will be required to deal with any local runoff generated in the immediate vicinity of the portal, and the section of the track sloping towards the portal.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



Portal 2F2

(NGL)

<0.1 584.21 584.22 0.35 0.15 0.5 584.7 <0.1 Low

Despite its low flood hazard a freeboard allowance higher that

what’s stated in Table 5 is recommended due to this piece of

infrastructure being a tunnel portal; to cater for localised runoff or unexpected incidents such as

burst water mains. The flood depths within the

vicinity of the proposed portal are generally less than 0.15m.

Portal 2G1

(NGL)

<0.1 582.80 582.82 0.35 0.15 0.5 583.3 <0.1 Low

Despite its low flood hazard a freeboard allowance higher that

what’s stated in Table 5 is recommended due to this piece of

infrastructure being a tunnel portal; to cater for localised runoff or unexpected incidents such as

burst water mains. The flood depths at the location of the proposed portal are generally

less than 0.1m. Approximately 80m west of the portal is an area

experiencing depths of up to 0.5m; however, the current levels in this location are lower than the

portal.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



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Location)

Notes



LINE 1 TBM LAUNCH LOCATIONS

TBM Launch 1B3

(NGL)

<0.1 622.16 622.22 0.2 0.1 0.3 622.5 0.1 Low

Despite its low flood hazard a freeboard allowance slightly higher that what’s stated in Table 5 is recommended due to this piece of infrastructure being underground; to cater for localised runoff or unexpected incidents such as burst water mains. The model results for the area around the perimeter of the TBM launch pit range from 0.1m to 0.17m, with velocities between 0.11m/s and 0.23m/s. Despite this low hazard, the excavation for the TBM will act as a sink for water if water is allowed to enter the site and the excavation as well as providing a route for water to enter the constructed tunnel. It is likely that flood water, laden with sediment and trash could severely affect the operation of the TBM.

TBM Launch 1F2

(NGL)

0.64 584.69 585.33 0.25 0.15 0.4 585.7 0.25 Moderate

The model results for the area around the perimeter of the TBM launch pit range from 0.06m to 0.13m, with velocities between 0.09m/s and 0.13m/s. Despite this low hazard, the excavation for the TBM will act as a sink for water if water is allowed to enter the site and the excavation as well as providing a route for water to enter the constructed tunnel. It is likely that flood water, laden with sediment and load could severely affect the operation of the TBM.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



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Location)

Notes



PARK-AND-RIDES

1-1 @ Station 1Y1

(NGL, west

of track)

0.35 652.98 653.33 0.2 0 0.2 653.5 0.03 Moderate Refer to Station 1Y1 notes

1-2 @ Station1H2

(AS, centre

of road, westbound

lane)

0.15 580.30 580.45 0.1 0 0.1 580.5 0.5 Low Refer to Station 1H2 notes

1-3 @ Station 1J2

(AS, centre

of road, northbound

lane)

<0.1 584.71 584.78 0.05 0 0.05 584.8 0.4 Low Refer to Station 1J2 notes


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

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Location)

Notes



2-1 @ Station 2G1

(NGL)

0.30 577.97 578.27 0.2 0.1 0.3 578.6 0.2 Moderate Refer to Station 2G1 notes

2-2 @ Station 2A2

(AS, centre

of road, SW-bound lane)

<0.1 653.54 653.64 0.05 0 0.05 653.7 0.11 Moderate Refer to Station 1A2 notes

OVERLAND FLOW PATHS & FLOODED UNDERPASSES – AT GRADE SECTION

Underpass at Abi Bakr As Siddiq (AS+CS, side of SW-bound lane, within underpass)

3.97 621.99 625.97 0.35 0.15 0.5 626.5 2 Extreme

Metro Line 2 passes underneath Abi Bakr As Siddiq Rd to the east of Station 2C2. The model shows that the depths in the vicinity of the station at ground level are generally less than 0.1m based on the local topography levels. There is flow along Abi Bakr As Siddiq Rd towards the underpass. On Abi Bakr As Siddiq Rd there is significant flood hazard posing a danger to so most vehicles and pedestrians. Within the underpass, water ponds up to depths of 3.97m. This depth of water will overtop the jersey barriers installed along the line.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



Underpass at Othman Ibn Affan (AS+CS, side of road, NE-bound, within underpass)

3.7 653.84 657.52 0.35 0.15 0.5 658.0 0.2 Extreme

Metro line 2 passes underneath Othman Ibn Affan Rd to the east of Station 2C4. The model shows that the depths in the vicinity of the station at ground level are generally less than 0.1m based on the local topography levels. Within the underpass, water ponds up to depths of 3.7m. This depth of water will flood the metro line, despite the presence of the jersey barriers.

King Abdullah Road (between 2C2 and 2C3) (AS+CS on side road adj. to SW-bound lane)

0.64 625.00 625.64 0.25 0.15 0.4 626.0 0.5 Significant

Water flows across King Abdullah Road at a low point; this was observed in the Nov’13 event. The 1:100yr peak flow at this location is ~12m3/s and occurs approximately 2.5 hrs into the storm event. Work to improve the stormwater network in the areas to the north of this location will provide partial mitigation incl. connecting this area into the Abi Bakr Culvert. However, this is unlikely to remove this risk.

Area NE of Station 2D2 1.16 613.29 614.46 0.35 0.15 0.5 615.0 0.2 Significant


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



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Estimated Flood

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Location)

Notes



Northeast of Station 2G1

(AS+CS, side of SW-bound

lane)

0.55 577.22 577.78 0.25 0.15 0.4 578.2 0.25 Significant

OVERLAND FLOW PATHS – ELEVATED SECTIONS

Area around Station 1Y1

(NGL to the west of the

track)

0.34 653.76 654.10 0.2 0.1 0.3 654.4 0.2 Moderate

Elevated tracks and stations are likely to be sufficiently raised to be protected against flooding. However, due consideration should be given to access and egress requirements, scour protection for support structures, and flood protection of at-grade infrastructure such as electrical equipment.


Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



Area around Station 1Z1

(AS+CS, centre of

road, southern part

of intersection)

0.38 646.72 647.10 0.2 0.1 0.3 647.4 0.8 Significant


Area around Station 1A1

(AS+CS, side road next to northbound

lane)

0.70 636.51 637.21 0.25 0.15 0.4 637.6 0.3 Significant


Area around Station 1F9

Note: Flood Model 1GHJ is currently being revised which is likely to result in changes in flood levels at Station 1F9. Flood risk information for this location will be included in Revision B of this report, anticipated to be issued during w/e 30th Jan 2015.

Area around Station 1G2

Note: Flood Model 1GHJ is currently being revised which is likely to result in changes in flood levels at Station 1G2. Flood risk information for this location will be included in Revision B of this report, anticipated to be issued during w/e 30th Jan 2015.

Area around Station 2A1


0.60 634.85 635.45 0.25 0.15 0.4 635.9 0.05 Moderate



Printed: 25-Jan-15





(m)

Estimated Existing



A (m AEA)



A+B (m AEA)

Estimated Flood

Velocity (m/s)

Flood Hazard


Location)

Notes



Area around Station 2C3

(AS+JB, centre of road, NE-

bound lane)

2.39 636.59 638.98 0.35 0.15 0.5 639.5 0.7 Extreme


# AS: Road Asphalt AS+CS: Bottom of Road Kerb Stone AS+JB: Bottom of Jersey Barrier, on Asphalt Level MY: Road Marking Lane Line Yellow NGL: Natural Ground Level

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