Flood Control Structures Considered for Kananaskis Country

by Tony Daffern on November 17, 2013

The Alberta Flood Recovery Task Force has proposed the building of three flood control berms with dry ponds behind them at the headwaters of the Elbow and Highwood Rivers within K Country, and a second set of berms in the foothills outside of K Country: one on the Highwood and one on the Sheep.

Berms

Source: Alberta Flood Recovery Task Force

The idea is that as stream flow increases during flooding, water would build up behind the berm forming a lake. The water would be released gradually at a maximum flow rate set by an outlet constriction until the area behind the berm is dry again and the stream confined to its regular channel. The proposed berms alone would not be enough to mitigate against all flooding, but they’d probably be able to bring the flow down to 2005 levels.

Berm picture

Artists impression of the proposed berm on the Elbow River (EQ1), east of Cobble Flats.

The initial spin is that a conduit would be installed in a river channel and a berm built over it. There would be a constriction in the conduit that would allow normal flow to pass through, but in flood conditions back water up in a dry pond. The water would continue to flow through the constriction at the designed rate of flow. Berm, conduit, dry pond. Sounds like no big deal!

However, this is far from the case. Perusing the limited information available to the public, it turns out these are massive structures 45–54 m high, 170–1135 m long and will store 12–84 million cubic metres of water (the Glenmore Reservoir stores about 17 million cubic metres). They are major engineering projects, either earth-filled berms in wider valleys or rock-filled dams in narrow canyons. While they don’t need a leakage monitoring system, they still need an impervious core because of the sudden build-up and draw-down of water. They will need a large amount of compacted fill over a wide base to ensure stability during extreme flooding when the dry pond may be full. The berms will also need overflow protection from waves and an emergency spillway to ensure the dam does not fail if water spills over the top. They will need significant (read concrete) outflow structures to control the flow as a single pipe is unlikely to work, and some form of protection at the inlet to prevent the inlets being clogged by debris. A spillway structure will be needed immediately downstream of the dam to reduce turbulence at the outlet.

So where are these berms likely to be built, how will they change the landscape, where will the fill for the berms be obtained from, and what will be the environmental consequences for the rivers and valleys above and below the berms?

It appears, interpreting the small map provided by the task force, that the berm on the Sheep is on private land outside of K Country. On the Elbow two berms are proposed, one a short way up Canyon Creek, the other in the narrow canyon east of Cobble Flats. The Highwood has one berm below the Bull Creek Hills downstream of Gunnery Creek, the second one is outside of K Country.

The effect on the ecology of the valleys will depend largely on the maximum flow rate that is set for the outflow. During any storm additional water would be added to the system through run-off downstream of the berms. Adding to the complexity is the time it takes for water to travel from the headwaters to the communities downstream. If the goal is to restrict the flow to 2005 levels at Bragg Creek, Turner Valley or High River, then the flow rate at the outlet will need to be set below 2005 levels, so we can expect that the dry ponds will accumulate water on the average every five years or so.

Information Table

Information Table giving dimensions etc.

The term “Fetch” is usually defined as the longest straight line across the impounded water from the face of the dam, and has implications for the height of waves that might pound or break over the dam during a storm. I suspect “Fetch” in this case means the longest distance the water will reach upstream when the dry pond is full (2.5 to 6 kilometers).

How much water accumulates behind the berm will depend on the flow rate and duration of the storm. Silt will be deposited across the valley floor and in the existing river bed. River banks will gradually collapse, taking trees and vegetation with them. If the valley floor is flooded too often it will become an unsightly mess of cracked mud and dead trees. If it is only flooded occasionally the area will become revegetated providing browsing for ungulates.

Downstream of the berm the river will continue to flow at the set rate. It will not receive the occasional flushing-out we are told is essential for a healthy river system and the accompanying riparian zone.

In the event of a severe mountain rain-on-snow event and/or extensive storms in the foothills such as we had in 2013 we could expect the dry pond to quickly accumulate water. The flow rate downstream from the berm would stay the same, but additional water added downstream would increase the flow to above the 2005 rate. In theory, the communities’ local protection would then kick in. Rivers downstream would get flushed out and there would likely be damage to infrastructure. Ecologically this would be little different from the 2013 flooding.

Upstream, thousands of cubic metres of silt would be deposited behind the berms as well as large tangles of roots and downed trees. In a worst-case scenario the dry pond would fill up and overflow the berm. Problems with debris would most likely reduce the planned flow at the outlet, putting significant stress on the berm’s embankment and outflow structure.

Large amounts of fill will have to be found near the construction sites and blasted rock may also be needed for some of the berms. Whether it is taken from the valley behind the berm to increase capacity or from adjacent hillsides it’s going to look ugly unless extensive restoration (revegetation and tree planting) is undertaken. Trees cannot be planted on the dam itself as the roots can weaken the structure. It may also be necessary to clear trees in the area to be flooded upstream of the dam to reduce the amount of debris carried downstream during the early stages of the flood.

The dam would require annual inspection and maintenance. Without maintenance there is increased risk of failure during extreme flooding. Think what would happen if the proposed dry dam on the Elbow were to fail catastrophically. Seventy million cubic metres of water would be released in a matter of hours—a rushing tidal wave of debris-laden water descending on Bragg Creek. Unthinkable!

The Task Force’s stated intention is to get these projects underway as soon as possible. Fortunately, environmental assessment is mandatory for structures over 15 m high and reservoirs with a capacity greater than 30 million cubic metres. Approval is needed under various provincial and federal regulations. In my opinion the Task Force has seriously underestimated the cost of these structures and has given little consideration to the watersheds immediately upstream. It is likely that if these project are given the go-ahead  the Alberta government will try to fast-track the approval process.

If these berms go ahead we need to ensure that we have input into their approval, planning, construction and landscaping.

Note: A 1969 Prairie Farm Rehabilitation Association study found the EQ1 site on the Elbow River to be a geologically unsuitable location for a permanent dam. Source Alberta Watersmart: Download A new report on historically identified detention and diversion sites Jan. 2014.

Check out the blogs on the Alberta Water Portal site for excellent information on re-wilding our rivers.

Updated February 2014

 

 

 

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{ 14 comments… read them below or add one }

Tyler April 29, 2014 at 5:04 pm

Everyone here brings up some really good points and I have to agree with what has been written. The whole idea is plain ridiculous. In my opinion this is not the solution. What I do want to know is, there was something on the radio today about what the proposed plan was. Did anyone else catch it? Or is it the same information that was posted by Tony months ago?

Tony Daffern January 31, 2014 at 12:46 pm

Here are some runoff figures presented by ESRD at a conference in Oct 2013. It’s difficult say how they relate to the proposed storage capacity as it all depends on the size of the outflow. The initial idea seemed to be to set the outflow so that the flow at Bragg Creek would not exceed 2005 levels. However, because of lack of data on major side creeks below the proposed dam and the main variables used to calculate Probable Maximum Flood or Input Design Flood, any calculation will have a high degree of uncertainty. Read: We won’t know if it works until we get another extreme flood! The engineers cannot allow catastrophic failure to occur – the consequences to Bragg Creek are unthinkable. This will result in an expensive structure with the upstream face covered in large rip-rap and a concrete emergency spillway.

Bow River at Calgary – flow in m3/s
1:100 year design flood 1970
2013 estimated peak flow 1740
2005 peak flow 791
1995 peak flow 499
1932 peak flow 1520
1902 peak flow 1557
1879-1897 peak flow 2265
Note: Dams built in several locations upstream since 1932.

Elbow River at Bragg Creek – flow in m3/s
1:100 year design flood 842
2013 estimated peak flow 959
2005 peak flow 671
1995 peak flow 803
1932 peak flow 836

Sheep River at Black Diamond – flow in m3/s
1:100 year design flood 714
2013 estimated peak flow 720
2005 peak flow 380
1995 peak flow 366

Note: 2013 peak flows estimated as gauges were damaged.
Source: Brian Hills, ESRD presentation at SEAWA
Below our Watershed Conference, Oct. 2013

Mark Lund January 30, 2014 at 11:46 am

Has anyone seen numbers for the total volume of water that passed through Calgary, Okotooks or High River during the 2013 floods? How do these figures relate to the proposed storage capacities… what is the likely hood these proposed dams will fill and spill over during floods similar to 2013??

ML

Tony Daffern January 28, 2014 at 10:24 am

The whole idea is scary. While these kind of dry dams may work in fairly flat landscapes, I can’t see them working on the fast, scouring, debris-laden streams of the Alberta foothills.
I have updated, corrected and enlarged the blog post today to reflect what I have learned in the last couple of months.

Peter January 28, 2014 at 9:15 am

thanks to our federal government’s recent changes to the navigable waters act, public consultation will be minimal if not non existent. The positive impact of these structures on flood mitigation will be short lived, the long term impact on our environment will be devastating. Besides: a plugged up culvert in an earth berm that is design for short term hold might become dangerous- the berm will leak and eventually fail. Remove the debris? Just look at Trans Alta’s trouble with the clogged turbines at Barrier lake. They need to drain the lake to remediate the turbine channel (basically a culvert..). Would that be at all possible with the proposed construction?

Heinz Unger December 15, 2013 at 1:08 pm

Thanks, Tony, for setting up this blog. As mentioned to you in person a couple of days ago, at the BRBC forum on Dec 11, additional dams were listed under the heading “Flood Mitigation Concepts: Bow” s follows: Dry dam west of Bearspaw Dam (BR1) [on the Bow River!], Dry dam on Ghost River (BG1), full service dam on Ghost River, Dry dam on Waiparous Creek (BW1), and Dry dam between Lower Kan. Lake and Barrier Dam. The summary table further states that the dams with names behind them “have been modeled in the Bow River Operational Model (BROM)”. Some folks supposedly have seen sketch plans of the proposed locations of at least some of these dams.

With regard to the proposed culvert control structures for the dry dams, I can send you a couple of photos I took last August of the twin culvert control structure that had been built by Transalta on their diversion of the North Ghost River many years ago. You’ll see that these large (2 – 3m) culverts were completely plugged by debris and caused a major failure of the entire Transalta diversion with uncontrolled flood flows reaching Lake Minnewanka and threatening to overflow Cascade Dam.

Jim Stelfox November 30, 2013 at 10:22 am

You’re right Ken. If aggradation occurs upstream of the dam due to bed-load material being deposited during the temporary backing up of flood water, then degradation (downcutting) of the river bed will occur downstream. While it would be possible to reduce aggradation by having a “canyon-style” opening in the dam, it would likely be much more difficult and costly than employing the culvert-style conduit, that they are proposing to use.

Ken Taylor November 29, 2013 at 3:40 am

Question for Jim Stelfox. You mention that a significant impact of these dams will be that they accumulate bed-load rocks and gravel upstream, and note that the cost of removing that annually needs to be budgeted. This assumes (I guess) the ‘conduit’ approach mentioned by Tony Daffern. However, if such bed-load is ‘caught’, and removed from the dry pond every year or so, then presumably the bed-load downstream of the dam is not renewed adequately, and bed erosion occurs over time downstream. Can these dams be built not with a culvert approach, but more a canyon style opening, so that while flow is restricted at high flow levels, some ‘normal’ level of bed load continues to be transported through. That would seem to more closely approximate natural conditions that one sees naturally in many places in the mountains where rivers go through canyons. Presumably that sort of historical natural constriction is exactly what has created the area we now call ‘cobble flats’, it is the dry pond.

Neil MacLaine November 21, 2013 at 6:09 pm

As a tax payer and lover of the river valleys, this idea scares me to death. The money would be much better spent on berms , public walkways and parks where the rivers pass vulnerable towns rather than turning beautiful upstream flood plains into gravel pits. Based on the short memories of governments, these structures will fall to neglect over the generations that may pass before the next comparable flood, and not perform as hoped for. If dams and reservoirs are the answer to extreme flooding events, why did the Kananaskis flood with 2 major dams upstream of the village, or the Bow with 3 dams between Canmore and Calgary?

Tony Daffern November 21, 2013 at 2:27 pm

During a speech to the Alberta Urban Municipalities Association on Nov 21, Premier Alison Redford announced that consultation and environmental reviews are set to begin on a diversion channel around High River and a dry dam upstream of Calgary. Here is what she said about the Elbow River dry dam:

“Elbow River dam project quick facts:
– The dry dam upstream of Bragg Creek would manage flows on the Elbow as they flow into Calgary’s Glenmore reservoir.
– The proposed dam would have a capacity of 44 million cubic metres.”

Note: The capacities for the 2 dams on the Elbow in the Task Force report were 12 and 70 million cubic metres!

Gillean Daffern November 21, 2013 at 1:51 pm

This is not the first time a “berm” has been proposed in the headwaters of the Elbow. 118 years ago, in July of 1895 and 1896, A O Wheeler, during his second and third year surveying the irrigation possibilities of the Foothills, identified the area we now know as Cobble Flats as a reservoir site. In 1916 a report written by the Committee on Water and Water-Powers likewise identified this area as a storage area, with a dam about 70 m high to be built just downstream of Canyon Creek. The storage area for the reservoir was given as 23,000 Ac Ft, which translates to 28.4 million cubic metres. (The present proposal is 70 million cubic metres.) To read more head to the Glenbow and check out “Water Powers of Manitoba, Saskatchewan and Alberta” written for the Commission of Conservation Canada by Leo. G. Denis and J.B. Challies.

Tony Daffern November 21, 2013 at 11:44 am

The only documents I have been able to find are Powerpoint presentations made during the The Alberta Flood Mitigation Symposium. The presentation by Richard Lindseth – “Community Flood Mitigation Advisory Panel” (second from last) has the information about the berms. Click on any of the pictures in the blog to go to the presentations.

Dave Mayhood November 21, 2013 at 11:06 am

Tony, could you post a link to the Alberta Flood Recovery Task Force documents describing this proposal?

Jim Stelfox November 19, 2013 at 2:27 pm

To my knowledge, there was no consultation with the Fish and Wildlife Division at the field level regarding this hair-brained scheme. Prior to retiring in mid-October, I was the senior fisheries biologist responsible for managing the fisheries in the areas where these berms are being proposed to be built. The first that I heard about this proposal was in October, when it was announced to the public.

In addition to the concerns clearly articulated in Tony’s article, the following also needs to be considered.

1. It is quite likely that upstream passage of fish will be restricted for part or all of the year by these berms. If so, this could have serious implications for the native populations of bull trout (recommended by COSEWIC to be listed as threatened), westslope cutthroat trout (currently listed as threatened) and mountain whitefish in these watersheds, if it prevents or inhibits fish from accessing traditional spawning areas.

2. Even if upstream movement of fish isn’t restricted, there are some spawning area upstream of the berms that will likely be lost due to deposition of sediments when water is backed up during a flood.

3. During floods, bed-load movement results in much more than just silt being carried downstream. Consequently, bed-load movement will likely rapidly reduce the storage capacity of these berms, thus necessitating removal of material every few years and causing further impact to the terrestrial areas upstream of the berms. The cost to periodically remove the accumulated sediments upstream of the berms needs to be added to the proposed construction costs, so that the public can see how much they will have to pay for what will amount to very little protection from future major floods.

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