3. Water Supply to the Ingleton and Chapel-Le-Dale Area
Having examined briefly the general criteria for reservoirs, it is logical to examine the valley of the River Doe. As flooding is not a major problem in the area, the strongest justification is to maintain water supply.
The water demands of Ingleton fluctuate with tourist population and Yorkshire Water have addressed this problem by importing water from the impounding reservoir at Embsay and from North West Water, to supplement Ingleton's own spring at Turbary Pasture, 6km to the north. It is interesting to note that the NWW import includes water from Haweswater impounding reservoir. Chapel-Le-Dale is self sufficient, receiving its water from a local spring. Table 1 shows the water supply for Ingleton and Chapel-Le-Dale.
Table 1 - YWA Supply Zones & Sources
| Water Supply Zone | Sources Supplying Zone | Source Type |
| Ingleton | Turbary
Pasture Embsay (Skipton) North West Water (Haweswater) |
Spring Impounding Reservoir Import |
| Chapel-Le-Dale | Chapel-Le-Dale | Spring |
From this it can be implied that on a demand basis, a reservoir local to Ingleton would reduce its reliance on imports, notably that from a competing company.
4. Geology of the Chapel-le-Dale Area
Steeply tilted Ordovician beds form the oldest series of rock types in the area and consist of undifferentiated siltstones, sandstones and conglomerates of the Ingletonian group and greywackes. These are unconformably overlain by Carboniferous limestones of the Garsdale and Danny Bridge groups. As can be seen in the local 1:50:000 solid and drift sheet for the area, Figure 3, the limestones have been completely removed in the valley bottom of the River Doe between Chapel-Le-Dale and Ingleton, by the same glacial processes that have left behind the various till deposits.
Figure 3 - 1:50000 Solid and Drift of Valley of River Doe (Sheet 50) (copyright IGS)
The presence of the river in the valley initially implies an aquitard, however in the upper reaches of the valley, this is probably more due to the presence of till than the hydrogeology of the underlying rocks, however, further down the valley, although waterfalls indicate changes in rock types, they remain relatively impermeable. The crucial point however is where the River Doe enters the valley, as Chapel Beck, close to Chapel-Le-Dale, at approximately 240 metres above ordnance datum. Although not shown on the solid map at this location, by deduction the unconformity between the Ingletonian Group and the limestones occurs between 220m and 240m AOD. Referring to the 1:25000 OS sheet, Figure 4, the presence of the unconformity is confirmed by the number of springs that issue along the valley between 230m and 270m AOD. Likewise, numerous caverns and sinkholes occur at or above the unconformity. If the Garsdale and Danny Bridge limestones were not already know as such, the information here would confirm their karstic nature, with high fissure porosity. The Ingletonian group below is less permeable, perhaps an aquitard.
Figure 4 - 1:25000 OS Sheet of Valley of River Doe (Sheet 2) (Crown Copyright)
Limestone is generally avoided as a dam foundation as excessive leakage can occur at the interface between dam and bedrock, especially where fissure porosity gives increased permeability, as is the case in the karstic limestone here. Seepage loss in limestone is invariably due to mass permeability or the pressure gradient. The mass permeability of surrounding bedrock can be reduced by blanket and injection grouting and cut off works. Impounding of water reduces the pressure gradient in adjacent ground and if there is a gradient from the reservoir then seepage will occur. A good understanding of the groundwater may establish a pressure gradient into the reservoir, preventing seepage losses. However, due to the presence of an extensive subterranean cave network, it is difficult to predict existing pressure gradients and flow networks, let alone what new pathways will open up during the life of the reservoir. In addition to the many potholes, White Scar Caves, a major local tourist attraction, at 250m AOD, would be flooded by a reservoir at this level.
Although dam construction on limestone is generally avoided, many examples exist of successful cases.