Breaking the Flow

Purpose: The purpose of our project was to see how effective dry dams are at reducing the velocity of a stream that has a high stream gradient or steep slope.

Background Information:

My sister and I chose to do this project because we understand that the unique topography of the Inter-Mountain Watershed District (IMWD) where we live poses more challenges when it comes to water conservation. We live between the northern edge of Riding Mountain and Dauphin Lake.

We wanted to gain a deeper understanding of what was being done to protect Dauphin Lake and tributaries in the district. We feel drawn to conserving and protecting our water as we have seen changes in the water at our favourite beach (Rainbow beach) over the years. We have noticed it getting more murkier and the sandbars extending longer into the lake. We have also noticed differences in the way some of the walleye we have caught from the southern end of Dauphin Lake looked in comparison to walleye we have caught in other lakes in Manitoba.

We wanted to know how effective dry dams were at reducing downstream flooding so to share the information with others in hopes that more land owners would work together with the IMWD to build them on their land.

Hypothesis: We hypothesize that our dry dam model with a high stream gradient will decrease the velocity of our stream by 8%.

Steps in our project:

Building models of a stream with a high stream gradient similar the Ochre River and Wilson River that flow into Dauphin Lake (2% and 1.9 %).

Measure the stream velocity and discharge using the Float Method.

Construct a dry dam on the model.

Repeat the Float Method using the same starting point and end point on the stream as used in step 2.

Calculate the difference in velocity in terms of a percentage.

Steps in the Float Method for measuring velocity:

Mark a starting point and end point of the distance of the stream (length) by using a stake, stick or other object. Measure the distance between the two. Use distance in feet.

Measure the width of the steam.

Calculate the average depth of the stream.

Have one person drop a bouyant object in the stream before the starting point.

Have a person record the length of time in seconds that it takes to travel from the starting point and end point marked out in your stream. Compete as many trials as you wish (the more trials the better accuracy) and calculate the average time in seconds.

Calculate the surface velocity of the stream by using the formula:

SV = Distance (ft)/ Average time (secs)

7.Calculate the adjusted velocity (AV) by using the following formula:

AV = SV x 0.85

8.Calculate the discharge or the stream CFS by using the following formula:

Discharge = Area x AV

Results:

We discovered that our dry dam models reduced the velocity of the streams by way more than we had hypothesized. The first dry dam was 27.3% effective and second was 39% effective for the second model.

A positive correlation existed between the velocity and discharge of the stream as well as the velocity and depth of the steam.

As we were able to find 3 dry dams in our watershed district, it was difficult to find historical data to show effective they were at the nearest stations where discharge was measured.

We also learned that there were other variable that we missed like the bed material and where the bouyant object is placed when measuring the stream (ie. the middle of the stream or closer to the far edge of the stream).

We also learned that measuring the streams in real life is way more easier than on models as we had to convert small measurements into the appropriate measurements like converting cm to feet for example.

Discussion:

Although it is difficult finding landowners willing to build dry dams or water retention structures on their properties as they temporarily retain water on their land, the benefits of reducing soil erosion, phosphorous loading and overland flooding downstream help to conserve Dauphin Lake in the long run.

In future research we would like to use other methods to measure water velocity such as using a flow-meter or a flow probe. We also would like to include water samples of Dauphin Lake to see how much phosphorus is in the water to include it in our research. The next step for us would be to use our data to promote the use of dry dams and other programs that the Inter-Mountain Watershed offers to conserve land and water.

We would like to give a special thank you to our mom for helping us throughout our project. My mom and kunshi (grandma) who supported us when it came to buying our materials. We would like to thank our great-grandpa Terry for getting us sandbags for our models.

We would also like to thank the judges at the Western Manitoba Science Fair for the encouragement and feedback.

Lastly, thank you to the IMWD for giving us valuable information and answering some questions of ours. Without everyone's help, our project would be incomplete.

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https://www.gov.mb.ca/sd/water/watershed/iwmp/dauphin/documentation/dauphin_lake_iwmp.pdf

Home. INTER-MOUNTAIN WATERSHED DISTRICT. (2024). https://www.imwd.ca/

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https://www.manitobacooperator.ca/news-opinion/news/local/farm-based-dry-dams-to-help-reduce-downstream-flooding/

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Manitoba Co-operator (Dry dams article)

Stevenson, L. (2016, December 19). Farm-based dry dams to help reduce downstream flooding. Manitoba Co-operator.

https://www.manitobacooperator.ca/news-opinion/news/local/farm-based-dry-dams-to-help-reduce-downstream-flooding/

Steinbach Online (Water drainage article)

Berg, A. (2025, September 17). After the storm: Understanding water drainage in the Southeast. Steinbach Online.

https://steinbachonline.com/articles/after-the-storm-understanding-water-drainage-in-the-southeast