BCTS Meeting in Chase, BC – February 6, 2024
This video presented at the meeting captures the main
characteristics of the watersheds feeding into the multiple springs
providing domestic water, stock watering and irrigation to the
farms below.
Highlighting the pooling area for ground and surface water (in the
marshy region), based on a sharp change in surface gradient and
vegetation, is likely correct. One could check further by carrying
out some geophysical profiling or borehole drilling to examine
where the water is going, where water is stored, and how deep
the glacial age sediment aquifer reaches before hitting bedrock;
however, this presentation is an excellent job of showing the
fundamental concerns related to the logging impacts on the
watershed both locally and provincially. Even if one carried out a
multiyear study on the local aquifers in this area, I doubt we would
come to a different conclusion.
There is also mapped limestone in the region, so it is not
impossible to have actual limestone karst connected to this
groundwater flow system, but more likely, the groundwater flow
appears to be dominated by a pseudokarst.
Although the near-surface subterranean conduits I examined
carrying water down from higher elevations above do have
evidence of calcium carbonate lining, suggesting dissolution and
deposition and sometimes blowing out, most of the channels are
best described as suffosional pseudokarst.
“Suffosional pseudokarst, or piping, results from grain by grain
removal of semi-consolidated and unconsolidated sediments
groundwater, where no solution is involved.”
Hence, in an area where there is abundant calcium carbonate in
the water, a lining of the groundwater channels in a pseudokarst
is not only possible, it is the norm. The fluffy low density likely
mainly loess and wind-blown sediment (glacial, lacustrine,
volcanic, wildfire-related) filled the gullies carved into till that
carpets calcareous quartzite bedrock worn smooth from the last
ice age as the glacial ice melted away to leave a glacial lake andlocal terraces and kettle/kame deposit (left during deglaciation).
Intense convective rain events likely ended up carving deep
gullies into the till straight down from the barren lake terraces and
glacial moraines left behind. At the same time, a very dusty period
post-glacial left widespread loess, or glacial-related dust, across
the landscape. With time, this material was preferentially
windblown into the former gullies into the till and any bedrock
channels carved by the glaciers or their rivers long ago.
Walking the region, one can see that there is less sediment on the
ridges between the gullies above the residential properties than
within the gullies. The water flows above the till but below the
surface in these gullies. Where bedrock or a clay layer lies below,
these pseudokarst subterranean streams are sometimes directed
back to the surface and then dive underground further downhill.
Concave areas of the slope will be locations where springs are
most likely, as shown on the slide presentation, and these cause
water to be discharged just above the homes and farms. Likely, a
clay layer from a lake that occupied the flat area where the farms
are located may also help direct water to the surface.
These pseudokarst channels are distinctive and vital for the
reliable supply of water to this semi-arid region.
High above the valley, the shaded north side of the hill has
maintained a snow forest where the mature and old-growth trees
have thrived. The forest likely increases the water collection in
your region by not only acting as a snow (and cloud droplet)
collection matrix but also the forest shades the snow so it will be
stored and released later in the spring and early summer than
otherwise would happen if the trees were not there.
The healthy mature forest also helps reduce the chance of
overland flow that can lead to flooding events and loss of summer
time water from extreme convective rainfall events.
In the channels I have examined, I identified several distinctive
volcanic ash layers, with the most recent likely from Mt Meager,
which erupted several thousand years ago near Whistler
Mountain directly west of this region. The fact that these drainage
gullies carrying your groundwater preserve these distinctive ashlayers strongly points to the long-term pseudokarst stability of the
water drainage in this region.
This distinctive way water travels downhill from the source areas
above the homes and farms, pools enroute, and continues to
maintain the springs is remarkable. However, evaporation would
likely be too high without this drainage system during the hot
summer months, and the water would disappear.
If these channels are examined carefully, one can also notice that
the trees do not grow in these drainage areas. They are shaded
glens bordered by large trees, and only in some locations does
the groundwater pop up to the surface and even then, only some
of the time. The trees can not grow where there is water all the
time; their roots will be deprived of oxygen, and they will
suffocate. Hence, the fact the trees remain on the margin of these
gullies and on the nearby ridges (where trees are scrawnier)
indicates that a consistently significant water flow occurs within a
few metres of the surface, sufficient to kill large trees directly in
the gully.
These gullies filled with soft silty loess are often filled with
burrowing gophers and other animals, but since one can trace the
volcanic ash layers, these animals are affecting only parts of the
channel deposits and not all of them.
The conclusion that logging in the area and driving up and across
these fragile channels will negatively affect families’ and farms’
water supply is reasonable.
Since these channels are so critical to the supply and storage of
water enroute to the water-licensed springs, and the water is
flowing within a few meters and likely no more than 10 metres
from the surface, these should be considered stream channels
and protected as such.
Hence, it seems reasonable that these should not be damaged for
each channel, and no cutting should be done for a distance of 30
m to 100 m or up to a distinctive break in slope marking the edge
of the gully and away from the edge enough not to trigger slope
failure.To describe the area of coalescing subterranean streams
(pseudokarst) above your springs as part of a larger watershed
that feeds water downhill is correct.
The exact delineation of each watershed may be in dispute, such
as on the southwestern fringe where the streams as drawn
diverge and migrate slightly out of the watershed as drawn, are
insignificant details, just related to mapping data set reasonable
errors.
The main story shown in this presentation is that the water
feeding the springs is highly dependent on the watershed
upstream.
We were told by the hydrologist working for BCTS that when the
trees are cut, there will be more water than has been recorded for
over two decades. The reasoning was explained by the fact that
the removal of the large trees will reduce evapotranspiration of
the forest and keep more water in the ground. Although it is true
the trees pump out large amounts of water, there are multiple
reasons why the forest, if preserved, would have a beneficial
effect on your water supply throughout the year while also
reducing the risk of flooding, increasing the snow and water
storage into the dry season, and also increasing the total amount
of water captured by the basin and delivered to the springs.
This is related to the average temperature on the forest floor,
which will be cooler when forested. Also, forested uplands tend to
be more humid even during the summer and help recycle water
from convective clouds onto the land and back again.
The forest, if removed, will likely result in greatly REDUCED
water to these springs instead of increased water.
Yes, there may be periods of intense flash floods, such as what is
not experienced with the mature pseudokarst drainage system
feeding these springs.
Intense precipitation events are increasing, especially during the
summer monsoon period of June through early August. If the land
above these farms and homes can not intercept the rainfall and
mitigate its intensity through underground flow and interconnected
storage areas, then the water will flow over the land, and deeplydissected channels will be the result, where we now have
pseudokarst drainage. It is possible these channels could erode
down to the glacial till and may take thousands of years to refill
with soft windblown sediment and again develop pseudokarst
drainage channels.
It is my expectation that the residents of farms will end up with a
much less reliable water supply system that could well end up
being dry by late summer and could develop debris flows/
landslides and deep dissections in gullies that now protect the
peoples’ water from evaporation – and interestingly also from
evapotranspiration because the trees can not grow in these
channels.
Based on my experience and examination of the geology and
hydrology in this region by these water licenses, I think what is
stated in this video and the concerns are valid.
If it were my home, I would be equally concerned, and I hope that
BCTS can agree not to log this critical area.
It is critical for more reasons than simply the destruction of local
water supplies in this fragile borderline desert – to snow forest
upland forest area. The many wildlife species that can thrive in
this rare refuge of old growth and mature growth and wetland
areas are important as well.
This area should be considered a rare refugia; due to the
excessive clear-cuts justified due to beetle kill, the massive
wildfires in recent years, and also the extensive clear-cuts and
continued development and farming nearby, these forests have
more value standing than cut for the public and even for the
BCTS.
I hope the value of this precious land and its water feeding
towards your property is valued by those in BCTS as much as I
think it should be for your sake and a better future for all.
My statements are those based on my personal opinion, ground
field studies, laboratory analyses, and decades of professional
experience that includes teaching university undergraduate and
graduate hydrology and Groundwater hydrology, Glaciology,
physical geology, general geology, post-doctorate in glacialhydrology and career work from USGS and Environment Canada
in the fields of glaciology, hydrology, meteorology, climatology,
and natural hazards.
I am currently the President of the PNW chapter of the
Association of Women Geoscientists, but this statement I make is
only based on my personal opinion, and it reflects only that. I
have recently retired from Federal employment with Environment
and Climate Change Canada, where I worked for almost 30
years. I do not represent them or the institutions where I have
been educated and employed and/or held an adjunct or visiting
professor position (University of Washington, CalTech, ETH VAW,
Western Washington University and University of
Saskatchewan).
Sincerely
Dr. Melinda (Mindy) Brugman, PhD Geological and Planetary
Sciences, BS Atmospheric Sciences, Revelstoke, BC