Attachment 12 Stage 1 Flood Risk Assessment (IE RP-0001)

Transcription

1 IE RP-0001, Issue A 17/10/2013 Attachment 12 Stage 1 Flood Risk Assessment (IE RP-0001) IE RP-0001_A_02.DOC

2 Flood Risk Assessment Celebrating 40 Years in Business Jazz Pharmaceuticals Ireland IE RP-0001, Issue: A Issue date:

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4 Contents 1 Introduction Requirements for a Flood Risk Assessment (FRA) 4 2 Stage 1 Flood Risk Identification Potential Sources of Flooding River Flooding Overland Flow Flooding From Artificial Drainage Systems Groundwater Flooding Risk of Flooding Arising from Proposed Development 11 3 Conclusion 12 Attachment 1 Drawing IE DR-0090 Rev. A Approximated Flood Risk Zone Resulting from River Cross IE RP-0001_A_01.DOC Page 3 of 12

5 1 Introduction PM Group has been requested by Jazz Pharmaceuticals Ireland (JPI) to prepare an Environmental Impact Statement (EIS) as part of a planning application for its proposed development known as. As part of the EIS, a Flood Risk Assessment (FRA) is required to assess the risk of potential flooding to the proposed site. This report contains the first stage of an FRA which involves identifying whether there may be any flooding or surface water management issues related to the proposed development site that may warrant further investigation. The proposed development site in question is located in the western environs of Athlone in Monksland, Co. Roscommon. The River Shannon flow southwards approximately 3km to the east of the proposed site, while a tributary of the River Shannon, the Cross River flows eastwards along the southern boundary of the site. These two rivers are considered to be the most likely sources of flooding at the site, but other potential flood sources such as on-site drainage and groundwater flooding have also been considered as part of this Stage 1 Flood Risk Identification. 1.1 Requirements for a Flood Risk Assessment (FRA) The government recognises the significance of flood risk and the need to integrate flood risk assessment and its management into the planning process. The following is taken from The Office of Public Work s (OPW) guidance document and highlights the need for an FRA to be carried out for this proposed development: At the project level, development either exceeding the specified thresholds for Environmental Impact Assessments (EIA) or development under the thresholds but with significant environmental effects and in an area at risk of flooding will require an EIS. Flood risk will therefore need to be an integral part of the EIA process. Screening for EIA should be an integral element of all planning applications in an area at risk of flooding. IE RP-0001_A_01.DOC Page 4 of 12

6 2 Stage 1 Flood Risk Identification According to the OPW guidelines, a Stage 1 Flood Risk Identification is a desktop study which is carried out to identify whether there may be any flooding or surface water management issues related to a plan area or proposed development site that may warrant further investigation. The following sections of this report details the Stage 1 Flood Risk Identification that has been carried out for the proposed JPI development site. 2.1 Potential Sources of Flooding The following are considered to be all potential sources of flooding for the subject site: - River flooding - Overland flow - Flooding from artificial drainage systems - Groundwater flooding - Risk of flooding arising from proposed development 2.2 River Flooding River flooding occurs when the capacity of a watercourse is exceeded or the channel is blocked or restricted, and excess water spills out from the channel onto the adjacent low-lying areas (the floodplain). This can occur rapidly in short steep rivers or after some time and some distance from where the rain fell in rivers with a gentler gradient. Flooding that results from a river or a stream is known as Fluvial flooding. The two rivers that could potentially cause fluvial flooding at the proposed development site are the River Shannon and one of its tributaries, the Cross River Cross River The proposed development is located adjacent to and within the catchment of the Cross River, which is a small tributary of the River Shannon. The river rises in the Brideswell area, approximately 7km to the north west of the proposed site and meanders through the lowlands to the area west of Athlone town for a distance of approximately 10km prior to its confluence with the River Shannon to the south of Athlone town, approximately 5km south west of the proposed site. The river also has a number of minor tributary streams along its course. The river is located in the Shannon River Basin District under the Water Framework Directive. Flow data collection by the EPA for the Cross River was ceased in August The flow for the 12 months before this was reviewed as part of this FRA. The data was obtained from a location downstream of the proposed site at Summer Hill. The river was reported to have an average flow rate of 1.81m 3 /sec. over this period. The maximum flow rate for this period was 11.22m 3 /sec while the minimum flow rate recorded was 0.32m 3 /sec River Shannon The River Shannon rises in a spring fed pool, the Shannon Pot in the Cuilcagh Mountains on the Cavan-Fermanagh Border at an elevation of 150m and its headwaters drain the raised mountainous regions around Lough Allen. On leaving these elevated areas, the Shannon winds its way through the drumlin masses of South County Leitrim and flows through Lough Ree and Lough Derg before reaching Parteen Weir. The river is characterised by slow flowing lacustrine expanses meandering between callows, bogs and wetlands, frequently breaking its banks in periods of flood and widens to several solution lakes along its course. The Shannon with its series of natural and artificial controls has a slow hydraulic response to incident rainfall. The system is considered in four main sections: IE RP-0001_A_01.DOC Page 5 of 12

7 - Upper Catchment Source to Lough Allen outlet; - Middle Catchment Lough Allen to Lough Ree outlet; - Lower Catchment Lough Ree to Parteen Weir; - Downstream of Parteen Weir. The site in question is located approximately 3km west of the lower catchment of the River Shannon at its closest point. The lower catchment has an area of 5,833km 2. The bulk of the lower catchment, including the catchment of the River Suck (the largest tributary of the Shannon with a catchment area of 1,619km 2 ) feeds into the Shannon upstream of Lough Derg. This section between Athone to Meelick is the worst effected by flooding in the catchment. The channel capacity is inadequate due to very low natural gradients (approximately 1:20,000) and a number of the previous studies have suggested that siltation of the channel has recently worsened flooding. The outlet from Lough Derg feeds into a channel about 3.5km long and then into an artificial reservoir about 4.5km long. The level of this reservoir is controlled by the sluice barrage at Parteen Weir and Power Station at Ardnacrushna. This channel and reservoir restrict the outflow from Lough Derg. The reservoir upstream of Parteen Weir is contained partly by two embankments Ardclooney at the West and Fort Henry to the East. Due to the distance between the proposed site and the River Shannon, and the fact that any previous flood events associated with the River Shannon has not affected the proposed site, as discussed in Section below, it is considered that the River Shannon does not pose any flood risk to the proposed site Office of Public works (OPW) Flood Hazard Maps and Hydrometric Stations Figure 2.1 illustrates a flood map history report for an area within 2.5km of the centre of the site. There were three reports of previous flooding recorded in this area; two of which can be attributed to the River Shannon. However, neither of these flood events affected the proposed JPI development site. The OPW has produced draft Preliminary Flood Risk Assessment (PFRA) maps for consultation. While these maps are based on high level data, they are of great value in indicating areas of potential risk. These maps are readily available from the OPW website. Draft Drawing No. 2019/MAP/249/A PFRA Indicative Extents and Outcomes is presented below in Figure 2.2. Figure 2.3 is a blow up of the proposed development site and its surrounding area from Figure 2.2 and illustrates that the south west of the site is at risk to fluvial flooding during a 1 in 100 year storm event (blue), while the south east of the site is a risk of fluvial flooding during an extreme storm event (light blue). In addition, drawing IE DR-0090 Rev. A has been included as Attachment 1, which illustrates the approximated flood risk zone on the site resulting from the River Cross, based on the OPW s PFRA. Therefore, in order to prevent any damage from potential fluvial flooding, the facility should not be located in this southern portion which is considered in risk of flooding. IE RP-0001_A_01.DOC Page 6 of 12

8 Figure 2.1: OPW Flood Hazard Map within 2.5km of centre of the site IE RP-0001_A_01.DOC Page 7 of 12

9 Figure 2.2: Draft Drawing No 2019/MAP/249/A PFRA Indicative Extents and Outcomes IE RP-0001_A_01.DOC Page 8 of 12

10 Figure 2.3: OPW s Preliminary Flood Risk Assessment (PFRA) of proposed development site IE RP-0001_A_01.DOC Page 9 of 12

11 As the majority of the proposed development site is not considered to be at risk from fluvial flooding according to the OPW s PFRA maps and considering that there has been no previous flood events recorded at the site, the risk of damage to the facility resulting from fluvial flooding at this site for the purposes of this Stage 1 Flood Risk Identification is considered to be low to nil. 2.3 Overland Flow Overland flow occurs when the amount of rainfall exceeds the infiltration capacity of the ground to absorb it. This excess water flows overland, ponding in natural hollows and low-lying areas or behind obstructions. This occurs as a rapid response to intense rainfall and eventually enters a pipe or natural drainage system. The natural lie of the land on the proposed development site is from north to south. The land to the east of the site is developed with drainage systems in place, eliminating any potential of overland flow on the site from the east. The land to the west of the proposed JPI site is a greenfield area which also slopes from north to south towards the Cross River, eliminating any possibility of overland flooding on the site from the west. From a desktop investigation of the land to the north of the site, the R362 road runs east/west approximately 300m from the site. There is drainage in this road that will ensure that any excess surface water to the north of the road will be drained appropriately and will not pose any risk to the JPI site. Therefore, the only area of land that could cause overland flow flooding at the proposed development site is the section of land between the R362 and northern boundary of the site. The majority of this land consists of greenfield areas, with a few residential dwellings located towards the south of the land. The area of land is approximately 23 acres. There is a drainage ditch which runs along the northern boundary of the site which is currently capable of draining any excess surface water from this portion of land. It is expected that this drainage system will remain in place following the completion of the development. However, if it is removed, suitable artificial drainage will be installed to carry any excess surface water from this land. Therefore, the risk of flooding of the site from overland flow is considered to be low to nil. 2.4 Flooding From Artificial Drainage Systems Flooding from artificial drainage systems results when flow entering a system, such as an urban storm water drainage system, exceeds its discharge capacity, and the system becomes blocked, and/or cannot discharge due to a high water level in the receiving watercourse. This mostly occurs as a rapid response to intense rainfall. Together with overland flow, it is often known as pluvial flooding. Flooding arising from a lack of capacity in the urban drainage network has become an important source of flood risk, as evidenced during recent summers. The proposed development site is a greenfield site and as such there are no existing artificial drainage systems. There are no artificial drainage systems to the north or west of the proposed development site as they are also greenfield areas. To the south of the proposed development site is the Cross River. Finally, to the east are further greenfield areas, together with Monksland Industrial Estate and Monksland Wastewater Treatment Plant (WWTP). Stormwater sewerage within the vicinity of the proposed development is provided by a combination of land drains (open field drains) within the greenfield areas and separate stormwater sewers within the nearby Monksland Industrial estate. The stormwaters within the Monksland Industrial Estate are discharged to an open ditch which runs along the eastern boundary of Plot B at a distance of approximately 125m upstream of the River Cross. A meeting was held with Roscommon County Council (RCC) on 2 nd July 2013, and it was confirmed that to the best of RCC s knowledge, there have not been any problems in relation to flooding on the proposed site as a result of the stormwaters from Monksland Industrial Estate discharging to this ditch. A site visit by PM Group on the same day confirmed that there is no pipework in place within the ditch for drainage purposes. The open ditch is at least 1m deep and approximately 1.5m wide. IE RP-0001_A_01.DOC Page 10 of 12 EPA Export :23:24:40

12 In addition, due to the close proximity of the entry point to the Cross River, there is no risk of flooding for the development of Plot A of the site and it is unlikely there will be any risk of flooding in any subsequent development in Plot B of the site. It is concluded that the risk of flooding from artificial drainage systems is low to nil. 2.5 Groundwater Flooding Groundwater flooding occurs when the level of water stored in the ground rises as a result of prolonged rainfall to meet the ground surface and flows out over it, i.e. when the capacity of this underground reservoir is exceeded. Groundwater flooding tends to be very local and results from interactions of site-specific factors such as tidal variations. While the water level may rise slowly, it may be in place for extended periods of time. Hence, such flooding may often result in significant damage to property rather than be a potential risk to life. A site investigation was carried out between November 2005 and February 2006 by Site Investigations Ltd. for the western half of the proposed development site as part of the preparation of an EIS for a previous planning application. Groundwater levels measured during this investigation varied across the site with levels dropping off from north to south across the site in line with the natural moderate sloping gradient of the land. Water levels in the two trial pits, which were located in the centre of the field approximately, were recorded as 1.5m below ground level (bgl) in both instances. Whilst no data was available for the northern boundary of the site it is expected that levels are deeper due to the increased gradient and levels close to the Cross River are likely to be shallower due to their proximity to the river. The groundwater flow direction at the site is likely to be in a north to south direction towards the Cross River, due to the natural gradient decline of the site topography towards the river. It should be noted, however, that water levels noted during this site investigation do not generally give an accurate indication of the actual groundwater conditions as the trial pits and borehole are rarely left open for sufficient time for the water level to reach equilibrium. Further site investigation will be required, to determine the equilibrium groundwater levels. The risk of groundwater flooding occurring at the site is considered low to nil and groundwater levels will be managed throughout the design. 2.6 Risk of Flooding Arising from Proposed Development The proposed development will be designed so as not to cause any increase in flooding within the catchment. In general, the site slopes from north to south towards the Cross River and the proposed facility will be laid to falls so that any excess surface water will flow towards the river. The site drainage systems will be designed in accordance with EN standards and the design guidance advised by the OPW Planning system and Flood Risk Management, Guidelines for Planning Authorities, Technical Appendices, In addition, surface water attenuation will be provided on site in accordance with the Greater Dublin Strategic Drainage Study (GDSDS) in order to control stormwater releases to the Cross River. Stormwater from a 1 in 30 year storm event will be attenuated on site, while stormwater from a 1 in 100 year storm event will be retained on site until the flood event alleviates. These measures will ensure that no buildings on site will be allowed to flood during a 1 in 100 year storm event. For any storm event with an intensity greater than that of a 1 in 100 year storm event, the excess stormwater will flow towards the Cross River due to the layout of the site as previously discussed. It can therefore be concluded that the flood risk arising from the proposed development itself is low to nil. IE RP-0001_A_01.DOC Page 11 of 12 EPA Export :23:24:40

13 3 Conclusion The purpose of this Stage 1 Flood Risk Identification was to identify if there will be any risk of flooding or surface water management issues related to the proposed JPI facility in Monksland, Co. Roscommon. - The report illustrates that there is the potential for the southern portion of the proposed development site to be flooded in a 1 in 100 year storm event, resulting from the River Cross, as illustrated in Drawing IE DR-0090 Rev. A, included in Attachment 1. - It is not expected that there will be any risk of flooding associated with overland flow, artificial drainage systems, groundwater flooding and the proposed development itself. - Therefore, it is considered that this Stage 1 Flood Risk Identification is sufficient and that it is not necessary to carry out Stages 2 or 3 of the FRA process. IE RP-0001_A_01.DOC Page 12 of 12 EPA Export :23:24:40

14 Attachment 1 Drawing IE DR-0090 Rev. A Approximated Flood Risk Zone Resulting from River Cross IE RP-0001_A_01.DOC EPA Export :23:24:40

15 NOTES N LEGEND N N N FORMAL ISSUE Jazz Pharmaceuticals JAZZ PHARMACEUTICALS IRELAND PROJECT ROCK Ordnance Survey Ireland Licence No. EN c Ordnance Survey Ireland/Government of Ireland APPROXIMATED FLOOD RISK ZONE RESULTING FROM RIVER CROSS IE :1000 IE DR-0090 EPA Export :23:24:40

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17 Met Eireann Return Period Rainfall Depths for sliding Durations Irish Grid: Easting: , Northing: , Interval Years DURATION 6months, 1year, 2, 3, 4, 5, 10, 20, 30, 50, 75, 100, 150, 200, 250, 500, 5 mins 2.5, 3.5, 4.0, 4.8, 5.3, 5.7, 7.0, 8.5, 9.5, 10.9, 12.1, 13.0, 14.5, 15.6, 16.5, N/A, 10 mins 3.5, 4.9, 5.6, 6.7, 7.4, 8.0, 9.8, 11.9, 13.2, 15.1, 16.8, 18.1, 20.1, 21.7, 23.0, N/A, 15 mins 4.1, 5.7, 6.6, 7.9, 8.7, 9.4, 11.5, 14.0, 15.6, 17.8, 19.8, 21.3, 23.7, 25.5, 27.0, N/A, 30 mins 5.5, 7.5, 8.5, 10.1, 11.1, 11.9, 14.5, 17.4, 19.2, 21.8, 24.1, 25.9, 28.5, 30.6, 32.3, N/A, 1 hours 7.3, 9.8, 11.1, 12.9, 14.2, 15.1, 18.2, 21.6, 23.7, 26.7, 29.3, 31.3, 34.4, 36.7, 38.6, N/A, 2 hours 9.7, 12.8, 14.3, 16.6, 18.1, 19.2, 22.8, 26.8, 29.3, 32.7, 35.7, 37.9, 41.4, 44.0, 46.1, N/A, 3 hours 11.5, 14.9, 16.7, 19.2, 20.9, 22.1, 26.1, 30.4, 33.1, 36.8, 40.0, 42.5, 46.1, 48.9, 51.2, N/A, 4 hours 13.0, 16.7, 18.6, 21.3, 23.1, 24.4, 28.7, 33.2, 36.1, 40.0, 43.4, 46.0, 49.8, 52.7, 55.1, N/A, 6 hours 15.3, 19.5, 21.7, 24.7, 26.6, 28.1, 32.7, 37.7, 40.8, 45.1, 48.7, 51.4, 55.5, 58.7, 61.2, N/A, 9 hours 18.1, 22.9, 25.2, 28.6, 30.7, 32.3, 37.4, 42.8, 46.2, 50.7, 54.6, 57.5, 61.9, 65.2, 67.9, N/A, 12 hours 20.4, 25.6, 28.1, 31.7, 34.0, 35.7, 41.1, 46.8, 50.4, 55.2, 59.2, 62.3, 66.9, 70.3, 73.1, N/A, 18 hours 24.2, 29.9, 32.7, 36.7, 39.2, 41.1, 47.0, 53.1, 56.9, 62.1, 66.4, 69.7, 74.6, 78.2, 81.1, N/A, 24 hours 27.2, 33.4, 36.4, 40.7, 43.4, 45.4, 51.6, 58.1, 62.1, 67.5, 72.1, 75.5, 80.5, 84.3, 87.4, 97.6, 2 days 33.8, 40.5, 43.8, 48.3, 51.1, 53.2, 59.7, 66.3, 70.4, 75.8, 80.3, 83.7, 88.7, 92.4, 95.4, 105.2, 3 days 39.4, 46.7, 50.1, 54.9, 57.9, 60.1, 66.9, 73.7, 77.9, 83.5, 88.1, 91.5, 96.6, 100.3, 103.3, 113.2, 4 days 44.6, 52.3, 56.0, 61.0, 64.1, 66.4, 73.4, 80.6, 84.9, 90.6, 95.3, 98.8, 104.0, 107.7, 110.8, 120.7, 6 days 54.0, 62.5, 66.5, 72.0, 75.3, 77.9, 85.4, 92.9, 97.5, 103.5, 108.4, 112.1, 117.4, 121.3, 124.5, 134.7, 8 days 62.7, 71.9, 76.2, 82.0, 85.6, 88.3, 96.2, 104.2, 109.0, 115.2, 120.4, 124.2, 129.7, 133.8, 137.0, 147.5, 10 days 70.9, 80.7, 85.2, 91.4, 95.2, 98.0, 106.4, 114.7, 119.7, 126.2, 131.5, 135.4, 141.1, 145.3, 148.6, 159.4, 12 days 78.7, 89.1, 93.9, 100.4, 104.4, 107.3, 116.0, 124.6, 129.8, 136.5, 142.1, 146.1, 152.0, 156.2, 159.7, 170.7, 16 days 93.8, 105.1, 110.4, 117.4, 121.7, 124.8, 134.2, 143.4, 148.9, 156.0, 161.8, 166.1, 172.2, 176.7, 180.3, 191.8, 20 days 108.2, 120.4, 126.0, 133.5, 138.1, 141.5, 151.3, 161.1, 166.9, 174.3, 180.4, 184.8, 191.2, 195.9, 199.6, 211.5, 25 days 125.6, 138.8, 144.8, 152.8, 157.7, 161.3, 171.8, 182.1, 188.2, 196.0, 202.4, 207.0, 213.7, 218.6, 222.4, 234.8, NOTES: N/A Data not available These values are derived from a Depth Duration Frequency (DDF) Model For details refer to: Fitzgerald D. L. (2007), Estimates of Point Rainfall Frequencies, Technical Note No. 61, Met Eireann, Dublin, Available for download at EPA Export :23:24:40