Flikr Photostream

www.flickr.com
Groat's Leadership photoset Groat's Leadership photoset

Friday, May 10, 2013

Devon Lions Campground

Preserving the Park

In the last few years, according to the Devon Lions and the Lions Campground Management, it is estimated that 6 to 8 feet of shoreline has been lost, in particular, in the area adjacent to the Campground office.  This, however, has never been actively marked nor measured for the purposes of quantification.  

Empirically, we are left with areal analysis to approximate rates of erosion.  Locals also point out the dogleg area of the roadway, being in greatest proximity to the river bank, as having significant potential for negative operational impact to the Devon Lions Campground.  This is the area widely considered to be of critical importance.


This area presents a significant concern due to the potential for interruption of traffic flows and normal operations of the campground.  An approximation of distance from top of bank to nearest roadway construction at the time of this photo was approximately 6.1 meters (approximately 19.7 feet), it has likely degenerated to a modest degree since the time of this areal image.  A foot inspection with GPS coordinate capture will establish baseline data starting in 2013.

Given the low average of erosion over the last two years (in accordance with local knowledge), the timeline to expected impact of operations, all else equal, would be some years away.  Using the 4-year longitudinal average at a rate of .7025 feet per year, the declination would be calculated as: (19.7 / .7025 = 28).  Enhanced flow level years, when overtopping occurred, is not believed to be inclusive in the four year comparison.  In general, it's safe to say the dogleg road area isn't likely wash out this year or even next year, even when adjusting for shoulder easement and safe foot travel area.

Erosion accelerates by a combination of volume and rate of the flow in the river.  In other words, the amount of water and how fast its flowing has a powerful impact on erosion rate.  Overtopping the bank, i.e. "the big flood", is a rare event and unlikely to cause substantial damage due to the overtopping itself.  Instead, it is the power of the river and the rate of river flow sustained during overtopping events that would have the most powerful impact on erosion.  This, of course, is why precipitation levels and dam release are central to a root cause analysis. 

Extraordinary flooding circumstances create some amount of erosion.  Project engineers from both commissioned firms, Peregrine and EBA, agreed when asked directly, that it is the quantity of water and the flow rate of the water, as controlled by dam release, that has, by far, the most considerable impact.

Geotechnical analysis should be focused on the area near the cabin, the dogleg, and the area with the minimum extent of bank coverage.  These were the sentiments agreed upon by the Lions in conjunction with the meeting of the Town of Devon representatives.  Upriver conditions were examined; visual inspections did not report visible tension cracks.  EBA states there is no risk of imminent riverbank failure.  The main roadway in the campground could be compromised to traffic well before the riverbank erodes to the point of contact. 

Most erosion occurs during the major water release periods from upriver dams.  This may happen in conjunction with heavy precipitation events or during times of high snowmelt and glacial melt.  Environment Canada records show the majority of precipitation is recorded from May through September.  Spring melt combined with substantial precipitation events probably carry the highest potential for overtopping.  The Peregrine consultant corroborated this information during her immediate post inspection visit and site de-brief.


Google Earth shots available to the public were used for riverbank erosion "rough" analysis.  Two data points by Google Earth applicable to this area were drawn from 2004 and 2008 data.  A line was drawn from the bottom (SE corner of the Cabin directly to the riverbank at approx. 85.xx degrees <1 degree variance and compared between the years 2004 and 2008.  The year 2004 shows approximately 59.23 feet and the 2008 image shows approximately 55.6 feet.  The rate of declination over the four-year period approximating 3.63 feet. 




A second analysis was done using a fixed infrastructure point.  In this case, the measurement was centered on a fixed point and extended to top of bank as imaged overhead.  The reduction of terrain appears to be approximately 2.81 feet in this case.  The rate of bank erosion varies from area to area.  Compensation was applied for a <1 degree variance, generally compensated by selecting an anchor point in line with extended vegetation and a clear demarcation of bank shading, indicating exposed face of the riverbank. 

Again, heading variance accounts for a minor distance variance, probably less than a couple of inches.  This measurement is subjective on the riverside anchor point due to vegetation changes and interruption of overhead resolution of image, yet it is probably a fair indicator.  Close examination also reveals lost vegetation, although the major trees appear to remain intact.  This could be the result of pruning or the result of smaller vegetative features eroding into the river.  It is impossible to detect this with a low-resolution satellite imagery and the measurement should only be considered a very rough estimate.



It seems unlikely that erosion rates would be consistent along the course of the area under study, and the predominant hydrological factor affecting rate would probably be the evident sand bar that exists in the river proximal to the area of the cabin.  Intuitively, it appears to have the effect of slowing rate in that area.  As river flow rate slows, sediment tends to fall out or "sink" which would create and sustain a feature like this sandbar. 

As the river passes that zone and proceeds down river, it seems to pick up speed, thus predictive of a more rapid rate of recession in the downriver area.  This presumptive estimate seems to have been borne out by measurements.  The EBA study focused on the same area provides no analysis as to the rate of declination of the land area.  Their overhead imagery is same source (Google Earth) with imagery taken from the 2008 posting of Google Earth.  The EBA study had no year over year comparisons or period over period analysis.  Although the bottom right corner of the image shows "2012", this refers to access year of the image by the Google Earth user.


The third area of analysis was set on the distal area of the driving road anchored in the central traffic division feature that existed at both points in time.  The 2004 image shows approximately 87.96 feet compared to the 2008 image at 81.71 feet, or approximately 5.25 feet of recession.  Once again, the downriver portion of the river study area appears to be showing a gain in velocity.  In Saskatoon, a confluence near an erosion riverbank area seemed quite similar to Washout Creek and suggested potential interplay with erosion rates near the confluence with the North Saskatchewan, potentially introducing another hydrological feature into the mix that could create increased bank instability, which, as noted above, has been an ongoing issue in the Saskatoon region.



The Bighorn dam created Lake Abraham, Alberta's largest man-made lake.  The Bighorn Plant generates enough electricity to supply the equivalent of 58,300 Alberta households.  The Bighorn embankment dam was built in 1972 in the mountain gap at Windy Point, in the Front Ranges of the Canadian Rockies, west of the confluence of the North Saskatchewan River and the Bighorn River and is managed by TransAlta.

The Brazeau Dam is located in Brazeau County of Central Alberta, 55 kilometres (34 mi) south-west of  Drayton Valley.  It was developed along the Brazeau River, at the confluence with Elk River, in the hydrographic basin of the North Saskatchewan River.  The Brazeau Dam is managed by TransAlta and produces 394,000 MWh per year, with a capacity of 355 megawatts. 

Since release from the Bighorn and Brazeau are, in times of large precipitation, largely interdependent,  the impact of water level and velocity are directly influenced by these two dams.  There are many factors that govern water release.  The upriver dams would both have considerable impact on flow rate and quantity.

The North Saskatchewan River is subject to the 1969 Prairie Provinces Water Board Master Agreement on Apportionment (PPWB), which states that Alberta must allow 50% of the natural flow of east-flowing rivers to enter Saskatchewan.  It also prescribes minimum flow required and water quality objectives (Alliance).  It is likely release rates would be managed, in part, to the PPWB master agreement.

The EBA project engineer who previously worked on the Shaw Conference Centre armoring, and a City of Edmonton official, both indicated there has been no effective way to generate release agreements designed to mitigate erosion between hydroelectric operators and individual municipalities.  It seems unlikely Devon would fare any better.  In addition to the requirements of the PPWB Master Agreement, there are the commercial considerations for power generation.  

Erosion appears blunted near the cabin due to the projection of the pronounced sandbar.  This is evidenced in the 04-08 erosion rate of 3.63 feet.  The natural velocity of the river should tend to be slow immediately proximal to the downriver side of the sandbar projection and then accelerate as it progresses past the cabin area.  This, in turn, should present by way of further erosion rates on downriver trend as is borne out by the 2004-2008 findings that show a similar rate of erosion at the dogleg of 2.81.  Cabin and dogleg measurements are similar for rates of erosion. 

The river apparently begins to pick up speed at third measurement point, advancing to a rate of 5.25 feet over the same period of time.  These measurements can be precisely calculated via surface GPS release floats, undercurrent speeds may also be calculated in a similar manner.  The findings corroborate intrinsic knowledge and logical inference.  Some flow rate and river level historical records may be consulted to examine concerns of overtopping due to severe floods.  Some photographs of overtopping events have been brought forward by local residents.

There are unknown hydrological implications of the washout creek confluence and the interplay of aquifer recharge upstream of the confluence.  Recharge influence over lateral instability could logically result in an alluvial presentation of erosion proximal to the confluence.  Local knowledge suggests there may exist one overflow pipe system for confluence drainage, probably designed for overtopping mitigation of Washout Creek.  Documenting and evaluating this drainage system may turn out to be an activity with merit.

The City of Saskatoon has battled riverbank erosion since the early part of the 20th century.  Numerous studies have been commissioned along with a variety of remediation efforts.  Much of their efforts have surrounded subsurface drainage systems in combination with berming of slopes and armoring of the riverbank.  Their situation is largely influenced by rate, flow, and discharge of urban influenced surficial aquifers and regional aquifers (A.W. Clifton, 1980).  Saskatoon has obtained favorable results with berming and riverbank armoring. 

To my knowledge, a stratographic assessment of the Lions Campground has never been done, which precludes an understanding of aquifer recharge implications relative to stratographic identification of potential erosion or "slide" areas.   There may be some merit in considering a stratographic assessment of drift and underlying till.  An image of the stratographic assessment of the 18th Street cross section from Saskatoon is included as a reference.


It is possible an inferred slip zone could be negotiated scientifically, but it should also be noted that intrinsic geologic understanding of this area could rule out the need to undertake such an assessment.  Stratographic interpretation has not been discussed by EBA or Peregrine, but have been components of both the City of Saskatoon and the University of Alberta College of Engineering studies cited herein.  In other words, the one integrated science both the commissioned reports did not have.  In the event of overtopping, such an assessment would seem to be more important relative to the inland embankment upon which housing is situated. 

Natural Resources Canada produced a comprehensive geoscape of the Saskatoon area (Canada N. R.).  NRCAN research also described coarse rock berms as a contra-erosion feature leveraged for bridge protection in low lying areas, which is in line with coarse rock berm armoring undertaken at the Shaw Conference Center.  Appropriate geological advice prior to discarding the idea of a stratographic study out of hand might be warranted, although it seems unnecessary to our goal of protecting the campground from lateral erosion of low-lying areas and preventing the loss of corresponding parkland features of the campground.


Geoscape contextualization demonstrates the integrated science approach to erosion analysis (Canada E. ).  Conducting a spatial imaging pattern recognition analysis of the river might be warranted.  This could be attained through the Government of Alberta archives for imagery and possibly accessing data from the Spatial Information Systems Laboratory (SISL) at the University of Alberta.  Academic dialogue with leading hydrological, geotechnical, geological, and geophysical resources should not be discarded out of hand when it is possible the SISL could  provide access to GIS data and mapping software at little to no cost with possible collateral interactions with multidisciplinary scientists.

One thing is certain; we are not alone.  Edmonton's river valley has also been the subject of considerable study.  In every study related to riverbank erosion that I have consulted, they have all included stratographic and topographic consideration of relative geology in the immediate area of concern.


Referenced is a study undertaken by the University of Alberta in conjunction with physical expansion of the University.  The study was headed by the Dean of the College of Engineering (S. Thompson, 1978).  The conclusion of that report spoke directly to lateral erosion.  The University of Alberta, the Shaw Conference Centre, and the City of Saskatoon implemented berming and riverbank armoring.  In the case of the University of Alberta, riprap facing was employed using a variety of sizes.  The sizes were carefully selected depending on calculated erosion forces given estimated flow rates.  The University of Alberta also concluded that lateral meandering is more significant than valley downcutting.

The University of Alberta study noted the economic cost for riverbank stabilization work to be substantial.  The annual cost of riverbank stabilization approaches the value of land protected, thus they argued the only case that justifies such measures would be those instances where it would impact public use and recreational activities… as is the case in Devon.

The Town of Devon and the Devon Lions Club are two highly impacted stakeholders.  As such, the Devon Lions Club have appointed by resolution of the General Membership, two representatives to liaise between the Devon Lions Club and the Municipality.  Areas of primary concern and action items outlined by the EBA study focus on continued bank monitoring and a structural engineering analysis of the existing walls and bank protection mechanisms to insure ongoing stability.  Plans are being developed to protect the campground from further bank erosion through the measure of adding "armoring" to the riverbanks.

The Town of Devon and the Devon Lions Club are two highly impacted stakeholders.  As such, the Devon Lions Club have appointed by resolution of the General Membership, two representatives to liaise between the Devon Lions Club and the Municipality.  Areas of primary concern and action items outlined by the EBA study focus on continued bank monitoring and a structural engineering analysis of the existing walls and bank protection mechanisms to insure ongoing stability.  Plans are being developed to protect the campground from further bank erosion through the measure of adding "armoring" to the riverbanks.

After considerable independent research, I agree that vulnerable zones should receive amoring, although the riprap should be properly determined as per the University of Alberta study.  Given my knowledge of the beliefs of the local people, I think armoring the high-risk sites, namely, the cabin to the dogleg area, would alleviate the highest concerns while protecting against the most expensive issue, the potential relocation of a roadway.  It is probably wise to explore an initial armoring phase in this area.  This would be a highly visible project providing physical reinforcement.

Riverbank armoring may not actually require approvals of other levels of government so long as equipment used to undertake the armoring is not required to enter the river proper.  This should be investigated at the outset of any planning to prevent any possible issues with other levels of government.

Both consultants suggested low precipitation months as being optimal for work scheduling.  Materials may exist by way of the Town of Devon sidewalk and curb replacement program rubble, or some form of riprap, appropriately sized and suitably esthetic.  Given the timelines, a planning phase could extend from early 2013 to late Spring 2013 or Summer, so as to accommodate public input and leverage a consultative process.  This would allow time to undertake ingress/egress arrangements to the riverbank at project commencement.  When river flow reduces in the Fall or early Winter of 2013/2014, work could be undertaken. 

Major improvements could be budgeted across fiscal years, with long-range ongoing investment through the 2014 - 2017 range if deemed feasible.  Further, a member of the Lions Club noted there was a pathway on the riverbank.  Given the River Valley Alliance (RVA) funding and the pre-existing path structures that connect the RVA, there may be some partial offsets to bank stabilization expenditures. 

There have been some discussions relative to making other changes in the River Valley.  These include an extension of the existing boat launch or possibly the addition of another boat launch.  Whatever these plans are, some amount of consideration should be given to those plans so that any work undertaken to prevent riverbank erosion would not create undue conflicts with future projects.  

Cited 

A.W. Clifton, J. K. (1980). Riverbank instabaility and development control in Saskatoon. Saskatoon: 1980.

Alliance, N. S. (n.d.). About the Watershed. Retrieved November 21, 2012, from North Saskatchewan Watershed Alliance: http://www.nswa.ab.ca/content/about-the-watershed

Almanac, F. (n.d.). 2013 Long-Range Weather Forecast for Edmonton, Alberta. Retrieved November 21, 2012, from Farmers Almanac: http://www.almanac.com/weather/longrange/AB/Edmonton

Canada, E. (n.d.). Environment Canada. Retrieved 11 18, 2012, from National Hydrological Resources Centre: http://www.ec.gc.ca/scitech/default.asp?lang=En&n=44EEFEB3-1#nhrc

Canada, N. R. (n.d.). The Trouble With Valley Slopes : Landslides. Retrieved 11 28, 2012, from Natural Resources Canada Earth Sciences: http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca.earth-sciences/files/pdf/sask/pdf/geoscape_southsask_landslides_e.pdf

EBA - A TERA TECH COMPANY. (2012). Riverbank Erosion and Stability Assesment North Saskatchewan River. Devon: A.F. (Tony) Ruban, M.Eng., P.Eng., Brian C. Adeney, P.Eng.

S. Thompson, D. T. (1978). River erosion and bank stabalization - North Saskatchewan River, Alberta. Edmonton: Department of Civil Engineering, University of Alberta.