15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 2A – NSRI “Soilscape” Soil Types in the Sandycroft Area; Used to Indicate the Predominant Underlying Soil Types and Estimate Standard % Run-off of Rainfall (SPR), within the Local Catchment. Key: ● – Loamy and Sandy soils with a naturally high groundwater and a peaty surface; ● – Slightly acid but base-rich Loamy and Clayey soils – slowly permeable and seasonally wet; ● – Free draining slightly acid Loamy soils; ● – River Dee; The Site at Sisters Yard is located on an area of free-draining sub-soils, comprising Medium dense silty fine grained SAND, which extends for at least 750m radius from the Site and is assessed as having a Standard Percentage Runoff (SPR) of ~ 14.5%, from data on a site with very similar sub-surface geology. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 2B – BGS Borehole Logs in the Vicinity of the Site. BH-SJ36NW251: A Borehole from June 1973, located ~65m N of the Site. Groundwater Standing Water Level (SWL) - 2.6m bgl. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 BH-SJ36NW429: A Borehole from October 1980, located ~100m S of the Site Groundwater SWL – 3.2m bgl. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 BH-SJ36NW259: A Borehole from June 1973, located ~145m NW of the Site. Groundwater SWL – 2.7m bgl. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 BH-SJ36NW296: A Borehole from January 1987, located ~190m NE of the Site. No Groundwater SWL was recorded for the upper Alluvial Deposits during construction of this Well. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 3 – Groundwater Vulnerability & Source Protection Zone Map. Key: ● – Minor Aquifer, High; ● – Minor Aquifer, Low ● – Major Aquifer, High; ● – Major Aquifer, Intermediate; ● – Inner SPZ (Zone 1); ● – Outer SPZ (Zone 2); ● – Total Catchment (SPZ 3); The Site is located in an area defined as a Minor Aquifer of High Vulnerability, located on free-draining sub-soils, which extends for at least 750m radius from the Site, beyond the western limit of a Total Catchment of a Major Aquifer for any Groundwater Abstraction in the area, with the nearest boundary of the Outer SPZ (Zone 2), approx. 2.0km to the south east. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 4A – River & Sea Levels. The nearest water course to the Site is a drainage channel called Broughton Brook, which becomes the o Sandycroft Drain where it turns NE by 90 adjacent to the B5129 (see Figure 4B). This drainage channel runs alongside the north western boundary of the Site within a relatively deep narrow gorge, ~5m to the NW of the north western boundary and ~4-5m below the level of the Site at it’s nearest point, flowing in a SSW - NNE direction to the northwest of Station Road and joining up with a number of other drainage ditches from the west of the Site and alongside the railway lines <100m to the SW, that drain the area of Sandycroft, before eventually flowing into the River Dee at a point approx. 400m to the NE. Broughton Brook is Tidal up to and beyond the point it is adjacent to the Site, but is protected behind an existing Penstock Flood Gate located ~350m NE of the Site, near the entrance into the Willow Brook Park Retirement Homes complex and the outfall of the stream into the River Dee. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 4B – Streams and Drainage Channels in the Vicinity of the Site. Broughton Brook originates from a small stream at Harwarden Golf Course and flows ~1.5km SE through a small reservoir before turning NE to drain the area to the S & SW of Hawarden Airport. It then flows N & NE until it enters a straightened channel running alongside Manor Lane to the junction with Chester Road and then WNW within a channel alongside the B5129 Chester Road until just past the junction with Station Road, where it is directed towards the NE and is renamed the Sandycroft Drain, flowing within a straightened channel to the NW of Station Road towards the River Dee, joining up with other drainage channels from the area and directed around the railway lines ~ 90m SW of the Site, before passing the Site <5m to the NW of the boundary and continuing NE towards the River Dee to outfall at a point ~400m NE of the Site. Other drainage channels named the Pentre Drain North & South continue alongside the B5129 ad drain the land south easterly towards the Sandycroft Drain and north westerly towards the A494, where it turns NE into a channel named the Queensferry Drain, that flows alongside the eastern boundary of the A494, until this main drainage channel also outfalls into the River Dee. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 5A – Flood Zones Map for Planning from Rivers & Sea. ●– Areas of a Floodplain which are developed but served by significant infrastructure, including Flood Defences - Flood Zone C1 (Based on EA Climate Change Flood Zone 2); ●– Areas of a Floodplain without any significant infrastructure, including Flood Defences - Flood Zone C2 (Based on EA Climate Change Flood Zone 2); ●– Areas Prone to Flooding in the past based on sediment evidence - Flood Zone B; The Site is shown as wholly located with a Flood Zone C1, which would be subject to an annual probability of flooding from Rivers & Sea as <1 in 1,000, without the presence of the flood defences along the channel of the River Dee channel. The presence of the flood defences effectively eliminate a number of the potential Flood Risk scenarios for the Broughton Brook/ Sandycroft Drain to flood, including much of the risk of inundation of the area around Sandycroft by tidal flooding across a wide area, which is protected against by the Levees along the Dee Channel. There is a potential for Extreme Tides to overtop the NW Levee along the Dee Channel that could cause Flooding beyond the estuary end of Sandycroft Drain, either due to inland flow of tidal waters, or due to drainage water from the surrounding area to the west, south and south east adding to the depth of tidal water in the Sandycroft Drain and adjoining land, becoming hydraulically locked in the channel and unable to discharge into the River Dee until the tide recedes and creating a flood either side of this (and other) drainage channel. Flooding as a result of a surge of Tidal Waters directly up the Sandycroft Drain up to the Site is prevented by the presence of a simple Penstock/ Clack Valve Flood Gate ~350m NE of the Site on the northern end of Sandycroft Drain. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 5B – Flood Risk Map from Rivers & Sea. ●– Very Low Risk Areas Prone to Flooding – <1 in 1,000/yr Probability; ●– Low Risk Areas Prone to Flooding - >1 in 1,000/yr but <1 in 100/yr Probability; ●– Medium Risk Areas Prone to Flooding - >1 in 100/yr but <1 in 30/yr Probability; ●– High Risk Areas Prone to Flooding – >1 in 30/yr Probability; When accounted for the Flood Defences along the River Dee Channel and the Flood Gate at the N end of the Sandycroft Drain, the Site is located entirely in a Low Flood Risk Area, although there is a small area of High Risk of Flooding adjacent to the Site’s NW boundary, but this does not impinge on the Site and is only shown as a small square because the Flood Map is completed as a series of pixels and at it’s lowest scale one (1) pixel is filled in, as the flood risk shown relates to water within the channel of the Broughton Brook/ Sandycroft Drain, which can become swollen due to very heavy seasonal rainfall and excess discharges of groundwater following very wet weather into the drainage network of this part of Queensferry and is predicted to occur within the 30yr return period. Blockage of the Sandycroft Drain by large volumes of debris flowing in the swollen stream following a peak rainfall event at the bridges upstream & downstream of the Site, is not a realistic flood scenario as the water flow in the stream will always be slow under any circumstances, due to the low lying topography of the area of Sandycroft. N.B: The latest flood modelling predictions for >1in100yr FLE’s undertaken by the EA in the area of the Site, incorporate allowances for Climate Change effects over the coming 100yrs. 15_705_YOUN1 – Sisters Yard, Deeside Flood Risk Assessment of the Proposed Multi-Pitch Travellers Site Rev.02 – August 2016 FIGURE 5C – Modelled Flood Event Map for the Defended 100yr + Climate Change Return Period around the Site. Modelling of the 100yr (Fluvial) Flood Events accounting for Climate Change has been undertaken by the EA and presented on the Map of the area shown above. This clearly shows that the area to the south of the B5129 Chester Road is predicted to flood at a return period of </= 1 in 100yrs, as is the western part of Harwarden Airport around the terminal building and the fields to the west.