Hydro G Final report - Kildare.ie

Hydro-G FINAL REPORT
EXECUTIVE SUMMARY
Leixlip Spa site in Co. Kildare is a wetland area which developed on five distinct terraces with shallow
bedrock and constitutes part of the Rye Water Valley Special Area of Conservation (site code:
001398). The site contains many rare and protected habitats and species including calcareous
grassland and petrifying tufa springs. The ecological monitoring of the wetland suggests that the site
has been drying out for the past two decades. Hydro-G was engaged by Kildare County Council to
investigate and evaluate water resources within Leixlip Spa, Co. Kildare to explain these ecological
changes and to a construct conceptual model of water movement throughout the site for future
conservation of the site. Investigation of local water resources included identification of springs and
seepages, in situ physiochemical analyses, hydrochemical analyses of selected discharge locations
and flow measurements. Results facilitated identification of different groundwater discharge zones
and conceptualisation of groundwater flow pathways within the site. Review of historical information
revealed that parts of the site were artificially modified which is likely to have impacted upon ecology
of the site. This data added to the developed conceptual model.
The findings of this study relate to monitoring conducted in December 2007 and January 2008, which
in hydrological terms represents a recharge period. Seasonal variations may occur.
The field monitoring and data analysis suggest that water at the Leixlip Spa site originates from a
complex groundwater system combining two sources. The main source of water comes from a
deeper, older and warmer groundwater system, discharging at the top of the first terrace through the
Spa Well. The second is a more recent, shallow groundwater that flows through the karstified
limestone bedrock with the main groundwater discharge located in the vicinity of the fen wetland
habitat (‘filtering ponds’) at the most elevated, southern terrace. Rainfall runoff also plays a part.
Hydrochemical analysis suggests that groundwater discharging from the warm spring at the Spa Well
is highly mineralised and is the dominant source of water within the site. It is also evident that
warm water discharging from the Spa Well drains northwards and flows into and through the shallow
system, resulting in water being mixed with more recently recharged water. Overland flow is also
apparent. The groundwater flow in the shallow system also occurs through conduits. Due to the
steep topography of the site, shallow depth of subsoil (if any) and karstic nature of bedrock,
groundwater can easily discharge through rock faces and later flow over ground toward the river Rye
Water. A number of discrete springs were noted at the 2nd and 3rd terraces. The physio-chemical
and hydrochemical analyses revealed that the Spa Well directly influences some conduit flows that
are relatively distant from the Spa Well itself and that waters on the 2nd and 3rd terraces are a
mixture of the Spa Well water and the shallow system groundwater. Water flow on the 4th and 5th
terraces originates mainly from surface runoff contributions from the more elevated upper terraces.
Hydrochemical analysis revealed also a leakage from the canal that occurs upgradient from the
wetland area at the first terrace but its contribution to overall water resources within the site is
relatively small.
Review of historical information revealed that the original outflow from the Spa Well was in the north
westerly direction. The historical evidence suggests that the outflow was diverted towards the north
easterly direction in late 1970s or early 1980s. Subsequently, water from the Spa Well discharges
into the ‘filtering ponds’ area that contains the cold springs. The implication of such engineering is a
limitation in water delivery to the western side of the 1st terrace manifested in drying of this wetgrassland
habitat. It is also possible that diversion of the groundwater flow away from the western
side of the 1st terrace occurred unintentionally during sewage works undertaken in 1980s. Analysis
of water quality within the Leixlip Spa site and in the Intel drain located at the western boundary of
the 1st terrace showed different hydrochemical signature in the drain than in all other samples from
the Leixlip Spa site suggesting different water origin. This further supports our interpretation that
Project No.: 07_136 -iv-
Leixlip Spa