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HomeMy WebLinkAbout2560309 - Other Assessments CONSULTING ENGINEERS BUILDING SURVEYORS DESIGN CONSULTANTS Tel: 042-9746492 Fax: 042-9746511 Email: info@cspringle.com Website: www.cspringle.com Registered Office: Monaghan Road, Castleblayney, Co. Monaghan. Incorporated in Ireland: Reg No 640491 MNK Engineering Ltd trading as C S Pringle Page 1 of 13 Flood Risk Assessment Newgrove Flood Risk Assessment Report Researched by: Marcus Dancey BSc (Eng), Dip Eng, CEng MIEI, FConsEI Chartered Engineer C S Pringle Monaghan Road, Castleblayney A75 EP84 Co Monaghan Date: 23rd July 2025 Requested by: Gallinagh Poultry Farms Ltd to support a planning application to Monaghan Co. Co. for the infilling of ground at Newgrove Location Address: Newgrove, Monaghan. Co. Monaghan. RECEIVED: 07/08/2025 Page 2 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers Background and calculations It is proposed to infill part of the property owned by our client located in a hollow within his property. This is an assessment of the flood risk entailed for these infilling works. The section of the site that is to be filled has been shown indicatively that it is at risk of pluvial flooding, i.e., that there is a depression in the ground which if not positively drained will fill up either temporarily or semi-permanently following rainfall. The following report refers to screenshots of maps and tables to address the issues. Screenshot shows the location of the area to be filled superimposed on the Preliminary Flood Risk Assessment of the pluvial flooding. The inner darker area of Orange represents the PFRA estimate of the 1:100 year pluvial flood while the outer line represents the PFRA estimate of the maximum extent of pluvial flooding. The PFRA shows that the site in question is not impacted by fluvial flooding which is shown in blue. The subject site and the field adjacent to the east is considered by the OPW PFRA to be subject to pluvial flooding. This is because the land lies in a hollow. The hollow has been piped, at an unknown date in the past but not less than 40 years ago, with a 225mm diameter pipe so that water is allowed to drain from the area and not form a permanent or even a transient lake/pond. RECEIVED: 07/08/2025 Page 3 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers This pipe is not sufficient to take the full flow from the catchment for low probability events and so for these events the pipe effectively acts as a throttle to the flow with water backing up to form an area of very temporary flooding. Such flooding occurs only for short periods of time following very heavy rainfall and quickly dissipates as the size of the pipe leaving the site is relatively large. Screenshot shows the location of the site in relation to the adjacent site to the east. The subject site is outlined in blue. The low point of the site is shown at A and drains across a field to be via an open sheugh. From there it flows in an open sheugh located along a hedge to C where it enters a pipe which drains the to an outfall at E via D and from there it flows in an open sheugh to entering the Ulster Blackwater River at F. This pipe from C to E is what prevents this fluvial flooding from happening. This is because if the pipe wasn’t there, the area to the west of B lies in a hollow and would become a shallow lake until it reached the level of the overflow contour somewhere between D and E. Its only outlet below this level would be the percolation capacity of the ground. However, because the pipe exists, the area is not subject to pluvial flooding. The contributing catchment area to the location is 8.597Ha. RECEIVED: 07/08/2025 Page 4 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers In our analysis of the situation, we approximate it to a standard attenuation design problem where the conservative assumption is made that the average flow from the catchment for the storm duration arrives instantly at the subject area and stops immediately when the rain ceases. With any attenuation calculation the total amount of water flowing into the subject area in a particular time duration is calculated knowing the area of the catchment contributing, the percentage impermeability of the catchment, the depth of rainfall that falls within that time for a given return period. The following table estimates the volume of water that flows from this catchment for a 100-year storm with a 1.2 climate change multiplier used in the calculations. The flow from the catchment is calculated as 104.1lts/s. The flow from the catchment is calculated as 104lts/s for a 100-year flow with a 1.2 multiplier for climate change applied. RECEIVED: 07/08/2025 Page 5 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers The area of the catchment has been measured as 8.59 hectares. The WRAP value is 3 so the soil value is taken as 0.4. The percentage impermeability is determined from the maximum flow from the catchment area as calculated using the IH124 equation (104.1lts/s) and a time of concentration using the FAA equation and the Kirby Kirpich method. The upper-bound Time of Concentration for the FAA equation is 26 minutes while the lower bound Time of Concentration for the same equation is 15 minutes. The Kerby method calculates the time of concentration to be 22 minutes. So, we assume that the time of concentration is conservatively 30 minutes. However, by way of safety factor we double that figure to 60 minutes to allow for uncertainty. Using this time of concentration and knowing the depth of water that falls on the catchment for this 60minute duration and knowing the size of the catchment we can determine the effective impermeability of the catchment. In this case it is 10.5%. Any shorter storm will have more intense rainfall but will not mobilise the entire catchment while any storm of greater duration will mobilise the entire catchment but will have a lesser intensity. Thus, the storm that equals the time of concentration will be the one which produces the maximum runoff calculated from IH124 as 104.1lts/s. As the basin is filling with runoff water the pipe draining the basin is conveying water away from the basin and into the river adjacent. The flow through the pipe at maximum head is 64.2lts/s. As this is less than 104.1lts/s (100 year storm *1.2 CC) the basin will start to fill with water until the rain stops. The maximum depth within the basin will happen at the time of concentration. Up until that time the head is less than the maximum head. For this reason, we assume, conservatively, that the average flow out is 0.7 times the maximum flow or 44.9lts/s. For the time of concentration at the point where we assume the whole catchment area to be contributing (60 minutes) 380.3m³ of water arrives at the site. During this time 161.8m² (44.9*60*60) leaves the site making a maximum storage requirement within the basin/hollow of 218.6m³. RECEIVED: 07/08/2025 Page 6 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers Estimate of the maximum volume of storage needed to be provided by the hollow. The maximum volume is estimated as 218.6m³. Rainfall depths are taken from the Depth Duration Frequency table obtained from Met Eireann. 35.1mm is the depth of rainfall expected for a 1:100-year storm of 60 minutes duration. This table is shown below. Knowing this volume that needs to be accommodated within the hollow and knowing the storage capacity of the hollow for depth of water stored we can determine the level to which the temporary storage will come to in order to accommodate that volume. This level is calculated as 56.324mOD. See below for table of volumes for levels. Given that a small part the site that is subject to flooding is planned to be infilled the volume will be reduced for the same level of water and so in order to store the same volume of water the water level must rise. This new level is calculated as 56.332mOD or 8mm additional height. Such an increase in level is considered insignificant. To give an indication of how insignificant this increase is to calculate how much time it would take to bring the level down to what it would have been had it not been filled. The time it would take is 186seconds or slightly over three minutes. So, the additional risk of an 8mm rise in the level of water lasts for just three minutes. The total 1:100-year flood disappears after 81 minutes. The soffit level of the pipe leaving the site is 55.7mOD so the depth of water is 0.624m. When added to the head loss in the pipe over its length of 0.6 then the overall head available to convey water is 1.224m. A friction loss in the length of the pipe of 1.11m plus a shock loss at the entry of 0.12m gives a total head loss of 1.23 which is approximately equal to 1.224m. RECEIVED: 07/08/2025 Page 7 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers The time of concentrations are derived from the FAA method and the Kerby method for overland flow. The upper-bound figure for the FAA method is 26 minutes while the lower-bound is 15 minutes. For comparison the Kerby method of estimating overland flow is 22 minutes. This is derived as shown below. The FAA equation shows the time of concentration as being somewhere between 26minutes and 15 minutes. The type of ground assumed is meadow. RECEIVED: 07/08/2025 Page 8 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers The Kerby method gives an overland flow of 22 minutes assuming the surface is “Average Grass.” RECEIVED: 07/08/2025 Page 9 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers Catchment area used by IH124 as determined accurately using LiDAR data. The area is 8.59Ha which makes IH124 the most suitable formula for calculating the runoff. Screenshot shows the rainfall for this location as 999mm as per Met Eireann figures for the location. RECEIVED: 07/08/2025 Page 10 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers Screenshot calculates the flow of water in the pipe when the storage is at its maximum height based on the flow characteristics of the pipe draining the site taking the friction coefficient, the entrance and exit coefficients. The average flow from the site is taken as 0.7 times the maximum flow which is conservative given that the flow through the pipe running full when there is no water being stored in the hollow is approximately 45lts/s which is approximately 0.7 times the full flow. Obviously, the surcharge of the water being stored will result in greater flows. RECEIVED: 07/08/2025 Page 11 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers The above screenshot shows the area of each of the contours within the flood-zone of the subject site and adjacent land. From these contour areas, the volumes of flood storage associated is calculated. Logrithmic interpolation is carried out. Table shows that for the volume of storage required of 219m³ the level of water within the hollow or basin is 56.324mOD before material is stored and 56.332mOD after the site has been filled. Map shows the extent of flooding when the water level reaches 56.4mOD or 700mm above the soffit of the pipe leaving the site. The height that the flooding reaches in a 100-year flood with 1.2 climate change factor added is 56.33mOD which is 70mm less than this level. As can be seen, most of the flooding takes place within the property adjacent to the east of the subject site. RECEIVED: 07/08/2025 Page 12 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers Map shows the extent of flooding when the water level reaches 56.4mOD when truncated by the fill material in the subject area. The volume displaced on the site being filled is 12m³. Depth Duration Frequency table for the Monaghan area. This is used to calculate the depth of rainfall that happens for any particular length of storm and of a given return period. RECEIVED: 07/08/2025 Page 13 of 13 Consulting Engineers Building Surveyors Design Certifiers Assigned Certifiers Residual risks Residual risks are the same as that which pertained prior to the proposed filling of the site which is that the entrance to the pipe leaving the depression could get blocked or partially blocked. Both the head and tail walls are properly done in concrete but there is no screen placed at the inlet. Given the insignificant difference in level or conditions between the filled and unfilled site it is not proposed to do anything other than to ensure that the entrance to the pipe is kept clear of growth and blockage. Conclusion In conclusion it has been calculated that pluvial flooding is possible for short duration storms of return period greater than 1:5 years. The basin has been piped with a 225 mm concrete pipe which drains the area in times of flooding so that the flooding dissipates quickly from the area. A 1:100- year storm with 1.2 climate change factor added will dissipate in 81minutes. The fill material proposed will rise the level of water in the basin by just 8mm in the area remaining. Such a volume is relatively small approximately 12m³ and is quickly dissipated in a time of 3.1 minutes. The increase in flood storage height as a result is insignificant within the context of a greenfield site of limited area and with no receptors of risk. The additional height of water store has no impact on the rate of flow into the Blackwater so that there is no change in risk downstream of the site. Thus, the proposed infill has no significant impact on risk of flooding adjacent or downstream. The residual risk is unchanged from what currently pertains and that is that the drainage from the site depends on the pipe being maintained and kept clear of blockage. Signed……………………………………………………. Marcus Dancey BSc (Eng), Dip Eng, CEng MIEI, FConsEI Chartered Engineer. RECEIVED: 07/08/2025 MONAGHAN LOCAL AUTHORITIES Water Protection Plan Checklist (To be accompanied by a Site Drainage Plan - Refer to Chapter 4 of Monaghan County Development Plan 2013-2019) General Site and Water Body Details Planning Ref. No. TBC Applicant Gallinagh Poultry Farms Ltd Townland Newgrove Water Supply Source Well X Co-ordinate 1 265214 Y Co-ordinate 1 334931 WMU 2 IE_NW_Blackwater RWB 2 Blackwater WB Status 2 Poor Objective 2 Restore 2021 Groundwater Vulnerability 3 L - Low Aquifer Importance 3 RK-Regionally important Proximity to nearest watercourse (culverted or open), wetland or lake (meters) 10m Proposed Development Is the development entirely or part of one of the following? (tick) Domestic dwelling Agricultural (cattle/dairy) Industrial-food related Public Works Agricultural (mushrooms) Industrial-non food Housing Agricultural (poultry) Quarrying/extractive industries Institutional Agricultural (piggery) Transport related Commercial/Retail Other agricultural – specify below Filling station/Fuel depot Mixed Use Development Other √ Waste Water Production and Treatment Method Domestic type waste waters Waste waters produced from any trade, food, preparation or business 4 Wheel wash, vehicle wash, cooling waters Waste waters produced from quarrying etc 4 Other waste waters 4 √ Construction phase waste waters Frequently asked questions for septic tanks may assist in the “fit for purpose” assessment refer to http://www.monaghan.ie/en/services/environment/water/waterawareness/faqforseptictanks/ Fuel or Outdoor Material Storage for Non Domestic Developments Number of fuel storage tanks existing or proposed on site? N/A Are fuel storage tanks bunded 5? N/A Detail liquid / feedstuffs / organic / chemical / waste oil storage on outdoor sites N/A Hard Surface and Open Yard Areas for Non Domestic Developments Footprint of proposed development including yard areas in m2 N/A Is there potential for soiled yard areas from material, product waste or manure handling, fuel dispensing, silt and soil, yard washing etc. N/A If yes, are silt trap(s), interceptor(s), soiled water tanks or other control measures shown on drainage plan? N/A Has the use of SUDS (Sustainable Urban Drainage Systems – http://www.susdrain.org ) been considered in the design of this development? N/A Development History – All Developments RECEIVED: 07/08/2025 Have previous pollution prevention planning conditions been complied with 6? N/A Does existing development have an up to date (as constructed) site drainage plan? N/A Is the existing/proposed development sewered or unsewered? N/A If unsewered, is the existing wastewater treatment system fit for purpose7? N/A Has the storm water drainage system been examined and/or surveyed for misconnections? (Information leaflet available from Environment Section) N/A Checklist of items to be included on Site Drainage Plan Location of lakes, watercourse, wells used for water supply, or karst features on or within 25m of domestic or 100m of non domestic development site √ Location of all drainage outfall points √ Foul water drainage system (in Red) √ Storm water drainage system (in Blue) √ Soiled yard area, soiled water drainage and management system, including silt traps, oil interceptor(s) and any SUDS facilities √ Location of waste water treatment facilities √ Location of fuel storage tank(s) √ Stream/Lake/Wetland/Riparian Corridors √ Footnotes and Useful Information 1 Projection in the Irish Grid 2 WMU, RWB, WB status. Objectives available on water maps at www.wfdireland.ie 3 Available in the public mapping section at www.gsi.ie 4 For information leaflets on Business Premises and Proper Use of Drains and information on discharge licensing see: http://www.monaghan.ie/contentv3/services/environment/formsguidesdocumentsdownlands/ http://www.monaghan.ie/contentv3/services/environemtn/water/waterawareness/leaftletsandguidelines/ 5 Guidance: www.envirocentre.ie Best practice for Oil Storage (BPGCS05) 6 Has certification of installation for previously granted wastewater treatment system been required and if so has it been submitted. 7 Refer to EPA Guidance at: http://www.monaghan.ie/contentv3/services/environment/water/waterawareness/faqforseptictanks/ and http://www.monaghan.ie/contentv3/media/monaghanie/content/files/pdf/environment/Water Pollution&DrainageSystems.pdf 8 Refer to Water Body, Sensitive Waters and Sensitive Land Maps in Chapter 4 of the Monaghan County Development Plan 2013-2019 Abbreviations WMU Water Management Unit RWB River Water Body WB Status Water Body Status IPPC Integrated Pollution Prevention Control Licence EIA Environmental Impact Assessment For Office Use: Sensitivity of Location Is the development located upstream of a high river quality site 8? Is the development located within a good status waterbody 8? Is the development located in the catchment of a water supply source 8? Is the development located within the Source Protection Zone (SPZ) of a groundwater supply source 8? Does the development require a discharge licence to surface or ground waters under the Water Pollution Acts? Risk to waters in relation to scale of development, previous planning/environmental history, IPPC or EIA aspects, site management and location in a sensitive area Applicant: Gallinagh Poultry Farms Ltd Date_08/07/2025______ RECEIVED: 07/08/2025 MONAGHAN LOCAL AUTHORITIES Water Protection Plan Checklist (To be accompanied by a Site Drainage Plan - Refer to Chapter 4 of Monaghan County Development Plan 2013-2019) General Site and Water Body Details Planning Ref. No. TBC Applicant Gallinagh Poultry Farms Ltd Townland Newgrove Water Supply Source Well X Co-ordinate 1 265214 Y Co-ordinate 1 334931 WMU 2 IE_NW_Blackwater RWB 2 Blackwater WB Status 2 Poor Objective 2 Restore 2021 Groundwater Vulnerability 3 L - Low Aquifer Importance 3 RK-Regionally important Proximity to nearest watercourse (culverted or open), wetland or lake (meters) 10m Proposed Development Is the development entirely or part of one of the following? (tick) Domestic dwelling Agricultural (cattle/dairy) Industrial-food related Public Works Agricultural (mushrooms) Industrial-non food Housing Agricultural (poultry) Quarrying/extractive industries Institutional Agricultural (piggery) Transport related Commercial/Retail Other agricultural – specify below Filling station/Fuel depot Mixed Use Development Other √ Waste Water Production and Treatment Method Domestic type waste waters Waste waters produced from any trade, food, preparation or business 4 Wheel wash, vehicle wash, cooling waters Waste waters produced from quarrying etc 4 Other waste waters 4 √ Construction phase waste waters Frequently asked questions for septic tanks may assist in the “fit for purpose” assessment refer to http://www.monaghan.ie/en/services/environment/water/waterawareness/faqforseptictanks/ Fuel or Outdoor Material Storage for Non Domestic Developments Number of fuel storage tanks existing or proposed on site? N/A Are fuel storage tanks bunded 5? N/A Detail liquid / feedstuffs / organic / chemical / waste oil storage on outdoor sites N/A Hard Surface and Open Yard Areas for Non Domestic Developments Footprint of proposed development including yard areas in m2 N/A Is there potential for soiled yard areas from material, product waste or manure handling, fuel dispensing, silt and soil, yard washing etc. N/A If yes, are silt trap(s), interceptor(s), soiled water tanks or other control measures shown on drainage plan? N/A Has the use of SUDS (Sustainable Urban Drainage Systems – http://www.susdrain.org ) been considered in the design of this development? N/A Development History – All Developments RECEIVED: 07/08/2025 Have previous pollution prevention planning conditions been complied with 6? N/A Does existing development have an up to date (as constructed) site drainage plan? N/A Is the existing/proposed development sewered or unsewered? N/A If unsewered, is the existing wastewater treatment system fit for purpose7? N/A Has the storm water drainage system been examined and/or surveyed for misconnections? (Information leaflet available from Environment Section) N/A Checklist of items to be included on Site Drainage Plan Location of lakes, watercourse, wells used for water supply, or karst features on or within 25m of domestic or 100m of non domestic development site √ Location of all drainage outfall points √ Foul water drainage system (in Red) √ Storm water drainage system (in Blue) √ Soiled yard area, soiled water drainage and management system, including silt traps, oil interceptor(s) and any SUDS facilities √ Location of waste water treatment facilities √ Location of fuel storage tank(s) √ Stream/Lake/Wetland/Riparian Corridors √ Footnotes and Useful Information 1 Projection in the Irish Grid 2 WMU, RWB, WB status. Objectives available on water maps at www.wfdireland.ie 3 Available in the public mapping section at www.gsi.ie 4 For information leaflets on Business Premises and Proper Use of Drains and information on discharge licensing see: http://www.monaghan.ie/contentv3/services/environment/formsguidesdocumentsdownlands/ http://www.monaghan.ie/contentv3/services/environemtn/water/waterawareness/leaftletsandguidelines/ 5 Guidance: www.envirocentre.ie Best practice for Oil Storage (BPGCS05) 6 Has certification of installation for previously granted wastewater treatment system been required and if so has it been submitted. 7 Refer to EPA Guidance at: http://www.monaghan.ie/contentv3/services/environment/water/waterawareness/faqforseptictanks/ and http://www.monaghan.ie/contentv3/media/monaghanie/content/files/pdf/environment/Water Pollution&DrainageSystems.pdf 8 Refer to Water Body, Sensitive Waters and Sensitive Land Maps in Chapter 4 of the Monaghan County Development Plan 2013-2019 Abbreviations WMU Water Management Unit RWB River Water Body WB Status Water Body Status IPPC Integrated Pollution Prevention Control Licence EIA Environmental Impact Assessment For Office Use: Sensitivity of Location Is the development located upstream of a high river quality site 8? Is the development located within a good status waterbody 8? Is the development located in the catchment of a water supply source 8? Is the development located within the Source Protection Zone (SPZ) of a groundwater supply source 8? Does the development require a discharge licence to surface or ground waters under the Water Pollution Acts? Risk to waters in relation to scale of development, previous planning/environmental history, IPPC or EIA aspects, site management and location in a sensitive area Applicant: Gallinagh Poultry Farms Ltd Date_08/07/2025______ RECEIVED: 07/08/2025