Fort Erie Creeks Watershed Plan - Niagara Peninsula Conservation ...

Groundwater flow is expected to be greater in the upper fracture bedrock and where there is contact
to overlying permeable sand and gravel lenses due to the contrast between the higher permeability
of this unit and the lower permeability of the overlying silt/clay unit and the underlying more
competent bedrock units. Groundwater is usually directed more locally to the stream reaches that
are in contact with the bedrock and more permeable alluvial sediments.
It cannot always be assumed that groundwater discharges to all wetlands. A large percentage of
the wetlands are perennial or intermittent recharge areas and as such provide a significant linkage
to groundwater particularly in the form of filtering out contaminants in the surface water entering
them prior to the water infiltrating into the groundwater flow system. It cannot also be assumed
that because of the predominance of clay that minor groundwater flow in the upper fractured clay
does not provide local linkages. It is noted that there is an intricate pattern of countless small,
shallow sloughs or seasonal pools connected by swales, resulting in complexes of swamp forest
sloughs within a network of slightly drier forest. Minor horizontal groundwater flow through the
shallow fractures in the clay may provide some level of local functional linkage.
The overburden and bedrock potentiometric (water level) maps presented in both the NPCA
Groundwater Study and the Water Resources of the Niagara Frontier and the Welland River
Drainage Basin study demonstrate only slight hydraulic gradients to the north and south and are
a more subtle reflection of the surficial and bedrock topography. This lack of gradient also
reflects the relatively lower permeability of the majority of surficial sediments. The Overburden
Potentiometric Surface and Bedrock Potentiometric Surface can be found in Figures 6 and 7 as
revised maps from Gartner Lee Limited, 1987.
The water level data utilized to construct overburden and bedrock potentiometric surfaces is
primarily derived from the MOE water well database. Bedrock and overburden wells in and around
the study area are shown in Figure 5a. The predominance of bedrock wells reflects the low potential
to develop water supplies in the low permeability overburden. It is important to note the relative
spatial and temporal limitations of the water well data. Spatially there a relatively small number of
wells particularly in the northwest portion of the study area. Interpolation of water levels from point
to point can be rather misleading and any subsequent use of the water level maps (i.e. Groundwater
Discharge, Upward Gradients) can be limited. In a temporal sense the water level data reflects static
levels at the time of the well installation and is not therefore a snap shop of water levels. Generally
these data are useful within an averaging context but given the lack of hydraulic gradient and in
some cases the lack of spatial data determination of specific groundwater flow directions,
particularly within the intermediate and local scale flow systems, cannot be quantified. A
dedicated groundwater monitoring well has been installed in the study area by the NPCA for the
Provincial Groundwater Monitoring Network. This shallow bedrock well was installed by Jagger
Hims Limited in 2003 within the upper Onondaga Formation at the corner of Hollow Bay Road
North and Old Garrison Road. Details of the well installation, a local hydrogeologic cross-section,
water level and water quality data are provided in Appendix ‘SW-D’. The water level hydrograph
shows seasonal variations of up to two metres. It can be seen that the lowest water levels occur later
on in the summer with recovery through the fall and early winter. The two metre seasonal variation
would be greater than the majority of hydraulic gradients within the local to intermediate flow
system setting.
March 2008 9 Fort Erie Creeks Watershed Plan
General Report (105116)