Figure E1 Location of Kenfig dunes NNR
Figure E2 Slack No. 9 (after Jones, 1993), Kenfig Dunes NNR, September 2008
Water levels within the slacks were universally much higher than average for late summer as a result of
g:\environment agency\424558 wet dune slacks\new base 13 may\figure 3.9b e1 and f1.doc
Figure 3.9b graph below - this is the best I can do with the resolution – please replace original with this if this is better – otherwise we will have to live with the figure as is.
Hopefully better resolution Figure E1 below. Please replace original with this if this is better
The humid dune slacks feature is a particularly important component at Kenfig and is represented by extensive and high quality examples (for example, Figure E2). It is strongly dependent on the shallow groundwater regime which maintains moist soils in the summer as well as periodic winter and spring inundation. The humid dune slacks also support formerly extensive but now declining populations of the two qualifying Annex II species represented at the site, the liverwort ‘petalwort’ Petalophyllum ralfsii and fen orchid Liparis loeselii (CCW, 2008).
Water level and basic climate monitoring at the site were initiated in the mid-1980s and continues to the present day. Interpretation of the results of this monitoring, along with wider hydrologically-related information, means that the hydrological regime is one of the better understood relative to other dune systems in England and Wales.
Environmental setting, Kenfig Dunes NNR
Kenfig NNR stretches 3 km north–south and 2–3 km east–west. The site represents the core part of a large hindshore-type dune system characterised by a dominantly west-east trending series of dune ridges and secondary (parabolic) dune slacks (Figure E3). Eighteen major parabolic slack complexes can be recognized, ranging from minor elements less than 100 m in length to larger forms which extend from the landward slope of the foredune ridge to the eastern boundary of the reserve.
Kenfig Pool, the largest (24 Ha) freshwater lake in South Wales, is located in the central, eastern part of the site. It is an expression of the dune system water table, is between 2 and 3 m deep, and its level fluctuates seasonally by c. 0.3 m.
The solid and drift geology underlying the site is complex. The general sequence from depth is:
• Carboniferous Limestones and Grits (major aquifer); • Triassic Mudstones (aquitard);
• Glacial Till (aquitard);
• Glaciofluvial Sand and Gravels (minor aquifer);
• Estuarine Clays and Alluvium (organic-rich clays and silts with beds of peat)(aquitard);
• Blown Dune Sands (minor aquifer); ranging from 0 m to at least 5 m thick.
Investigations and monitoring
For his doctoral research Dr Peter Jones examined the phytosociology of dune slack communities at Kenfig, and the influence of hydrology upon composition and structure of the vegetation. During this project an intensive shallow groundwater monitoring network comprising over 100 shallow (c. 1 m) dipwells (Figure E3) was established across the site.
The west-east orientation of the dune ridges and elongate dune slack systems meant that a significant proportion of the dipwells were arranged in west-east transects. One of these, usually referred to as the ‘main transect’ (Figure E3), was chosen for monitoring on a more regular basis than the remainder of the network. It is fairly closely aligned to grid line easting 820 and passes from east to west through some of the best examples of dune slack habitat. The selection of the transect for more regular monitoring was made on the basis of the following criteria:
1. It passes through the groundwater dome of the superficial dune system aquifer (Jones, 1993 and Figure E3) and thus for monitoring purposes is suitable for assessing the seasonal and longer term dynamics of the dome in relation to climate and other factors.
2. It is coincident with the line of widest lateral development of the perennial unconfined aquifer of the lower dunes, where sand extends vertically some distance beneath the water table.
3. The route of the transect is relatively accessible, clear-cut and easily walked, which aids monitoring and surveying.
The transect initially (1986) comprised eight dipwells. More dipwells were gradually added, partly as a means of providing a degree of back-up between adjacent sites to cover losses due to vandalism, and also to track the gradual easterly development of young dune slacks in an active area of dune evolution at the seaward, western end of the transect as slack floors gradually stabilised. The transect currently comprises 12 dipwells.
Water levels along the transect have been monitored at varying frequencies (rarely less than monthly) since 1986, and the resulting dataset represents an extremely valuable resource in both site-specific and generic habitat-type contexts.
Investigations and monitoring in support of an assessment of possible hydrogeological impacts of large-scale dewatering of Cornelly Quarry (and associated quarries) (3 km east-south-east of Kenfig Dunes) supplied additional information about the
Figure E3 Annotated aerial photograph of Kenfig Dunes NNR
Figure E2 Annotated aerial photograph of Kenfig Dunes NNR
young dune slacks in an active area of dune evolution at the seaward, western end of the transect as slack floors gradually stabilised. The transect currently comprises 12 dipwells.
Water levels along the transect have been monitored at varying frequencies (rarely less than monthly) since 1986, and the resulting dataset represents an extremely valuable resource in both site-specific and generic habitat-type contexts.
Investigations and monitoring in support of an assessment of possible hydrogeological impacts of large-scale dewatering of Cornelly Quarry (and associated quarries) (3 km east-south-east of Kenfig Dunes) supplied additional information about the groundwater system at and around the site from 2002 (see, for example, ESI 2003). A number of observation boreholes were installed both within the site, and between the site and the quarry, to provide information for the impact assessment and to facilitate enhanced groundwater monitoring.
groundwater system at and around the site from 2002 (see, for example, ESI, 2003). A number of observation boreholes were installed both within the site, and between the site and the quarry, to provide information for the impact assessment and to facilitate enhanced groundwater monitoring.
Rainfall has been measured continuously at the site since 2002, through a succession of different rain gauges in various positions.