AECOM
7
Gartloch and Gartcosh Hydrological Study
43
Summary
This document sets out to establish a baseline of the site to support the design study process by investigating all sources of flooding including fluvial and pluvial flooding under a range of annual exceedance probabilities (AEP). The report provides an assessment of flood risk from the watercourses in the area including a hydrological assessment to define the potential floodplain areas under various annual exceedance probabilities up to 0.1% (500yr return period). An additional allowance to account for estimated future climate change has being assessed for the 3.33% AEP and 0.5% AEP scenarios. The report includes an assessment of the sewerage system in the study area and its interactions with the surface water regime. The results show that no properties are currently at risk of flooding from the Tolcross, Whamflet, Molendinar or Bishop Burns. Approximately 16 properties along Inverary drive, south of Gartcosh, are at risk of flooding from one of the tributaries of the Bothlin Burn. The proposed development at Easterhouse south is affected by flooding from the upstream end of the Tolcross Burn, even at the 50% AEP event, caused by the restriction of the culvert at Commonhead. Flooding from the Whamflet Burn causes ponding of flood water on the M8 motorway, west of the Jimmy Young Bridge. Flood extents from the Bothlin Burn and its tributaries impinge on the boundaries of proposed development areas at Easterhouse north, south of Gartloch Pools, at Gartcosh south of Johnston Loch, and at Glenboig. Predicted flood levels should be taken into account when planning development in these areas. Relevant flood levels indicating the maximum water levels experienced during the 0.5% AEP event plus climate change are given in Table 7.1 below. Table 7.1 – Indicative design flood levels for future development Development location
0.5% + climate change flood level (mAOD)
Easterhouse south
77.5 – 73.75
Easterhouse north
78.25
South of Gartloch Pools
77.0
Gartcosh, south of Johnston Loch
79.5
Glenboig
82.0
7.1 Hydrogeology Although the quality and quantity of information collated in relation to local hydrogeology does not allow a very conclusive assessment, it is not considered likely, that there is significant interaction between local hydrology and underlying groundwaters and minewaters. Any minor interaction would not be significant in terms of the scale of flooding at any location. There is no indication of the disappearance, reappearance, or significant change in size, of surface water features or wetland areas on the historic OS maps reviewed, that could not be attributed to other factors (e.g. the construction of fish ponds and field drains). The limited known mine water discharges onsite and in the vicinity are of insignificant volume. Although it is dangerous to extrapolate, it is considered likely that, if any further mine water discharges were to form, they would be of a similar insignificant magnitude. The age of the mine workings is such that rebound is likely to be complete. It is therefore concluded that mine-water rebound is unlikely to affect surface water in the future.