The junction or point where two rivers or streams meet, where one flows into the other thus creating a single channel, is called a confluence. Usually one body of water is larger than the other and becomes the main river or creek as the water continues its path downstream. In some cases, a new river is named below the confluence of two rivers. A local example of this is the Thompson River. The North Thompson and South Thompson meet at Kamloops, BC, and together they form the Thompson River, which ultimately discharges into the Fraser River at Lytton. The larger river is called the main stem and the smaller river is called the tributary.
The contrast between the muddy waters of the mighty Fraser River and the clear and pristine-looking Coquihalla River is quite striking. What you see at this earthcache can vary greatly depending upon the time of year of your visit. During the spring freshet, both rivers are quite swollen and have repeatedly flooded the area where they meet. Later in the year, both rivers are significantly smaller than they are during the spring freshet. In the photo below, you can see the colour contrast as the Coquihalla discharges into the Fraser, and how the Coquihalla manages to force a small bit of clear water along the edge of the Fraser before its much smaller volume is overwhelmed by the larger Fraser. Of note is that during high water, the entire sand/gravel bar visible in this photo can be completely submerged, and the Fraser practically doubles in width.
Coquihalla River discharging into the Fraser River, Hope, BC.
In the paired photos below, you can see the difference in water levels during and after a flood event. Normally you can park by this sign. Despite the massive volume of the Fraser, the Coquihalla actually has a higher gradient and a higher energy proportionately. Gradient is a function of how quickly the river drops vertically over horizontal distance. Here, the gradient of the Fraser is much lower than it is at, say, Hell's Gate (the narrowest point in the Fraser Canyon). Likewise for the Coquihalla, it is certainly flatter here than in most places where it is visible along Highway 5.
The photo on the left was taken on May 20, 2018. The photo on the right was taken on June 18, 2018. You can see how much the waters have receded in one month.
In the photos below, you can see some of the flood control measures in place. This is Wardle Street looking SW (downstream) on the left and NE (upstream) on the right. Normally you can park at the end of Wardle Street (the parking coordinates for this cache).
Wardle Street, Hope, BC, in high water, looking in both directions.
The photo below was taken September 10, 2017. The view is from the edge of the Fraser looking south back to near GZ and your access trail down the river bank to the gravel bar. This entire area can be completely submerged at high water.
Gravel bar from edge of Fraser River, looking south back to GZ.
To log this Earthcache, please answer the following questions:
- At a confluence, what is the dominant river called? What is the secondary river called?
- Are the water levels high, low, or average at the time of your visit?
- From the edge of the road, estimate the vertical drop to the Fraser River. (This will vary greatly with the seasons).
- What is the size range of boulders you see near the confluence?
- Which river do you think has the higher gradient?
- Do you see any evidence of past flooding and, if so, what do you see?
- At the time of your visit, have any steps been taken to control flooding? If so, are these permanent or temporary?
- Please feel free to post photos of this earthcache and the general area.