This cache is placed as part of the Credit River Sea Creatures series. You can find this cache by floating down the Credit river in the water craft of your choice. The Credit River is typically shallow so one of the best ways to navigate the water is by floating on a river tube. Be aware that in sections the river becomes very shallow which may involve wading.
This earthcache is named for the Rock Beauty , also known as corn sugar, coshubba, rock beasty, catalineta, and yellow nanny This is a species of marine ray-finned fish, a marine angelfish belonging to the family Pomacanthidae and is found in the western Atlantic Ocean.
Earthcache
The focus of this earthcache is to look at the use of rocks, vegetation and possibly other man made interventions that have been used to stabilize the shoreline on the outside banks of the river, and to determine if these techniques are working based on your observations.
Current Erosion and Stream Stability Conditions of the Credit River according to the 2007 Credit River Water Management Strategy ( Making it work) document.
Upper Watershed
- Relatively stable
- Some tributaries unstable because of agriculture and urbanization
Middle Watershed
- Relatively stable
- In urban areas, streams unstable because of relatively steep gradient
Lower Watershed
- Moderately to highly unstable because of urbanization
Shoreline Erosion
Rivers that flow in gently sloping land tend to wander left to right making curves in the channel known as "meanders".
Meandering rivers occur when a river flows along a fairly flat or gentle slope. The constant flow of water, in particular during seasonal flooding or after a rain event can erode the banks where the water is flowing fastest, along outer bank. Sand and debris is carried downstream and is deposited along the inside banks where the water flow is slowest. The inside part of the curve is almost always the shallowest while the outside of the curve is deepest. Gravel bars can also form creating small islands typically along the inside curve of a meander, frequently found in much wider rivers like the Grand River or the Thames River.
Types of Erosion by Water:
Splash Erosion: Small soil particles are detached and sent airborne through the impact of raindrops on soil.
Sheet Erosion: Raindrops break apart the soil structure and it's moved downslope by water that flows overland as a sheet rather than definitive channels. This occurs frequently during cloud bursts.
Rill Erosion: This process develops small, short-lived, concentrated flow paths. These paths creates a sediment source and delivery system for hillslope erosion. Areas where precipitation rates exceed soil infiltration rates are more prone to this type of erosion.
Gully Erosion: Water flows in narrow channels during or directly following heavy rains or melting snow. The gullies can erode to considerable depths.
Valley or Stream Erosion: Continual water flow alongside land (along a linear feature) creates this type of erosion. It extends downward, deepening a valley, and headward, extending the valley into the hillside. This occurs most frequently in times of flooding.
Streambank Erosion: Over time, banks of rivers and streams are naturally worn down.
Water flow and its effect on erosion and deposition
Water flow is an important mechanism for both erosion and deposition. The flow of water is controlled by both the streams gradient and by the geometry of the stream channel.
Where a stream is narrow, the water flow velocity will be greater. Water flow velocity is decreased by friction along the stream bed, with the slowest flow at the bottom and along the edges and fastest flow just below the water surface.
Fun fact: velocity just below the surface is typically a little higher than right at the surface because of friction between the water and air.
On a curved section of a stream, flow is fastest on the outside and slowest on the inside. The gradient along the edge of a stream will also affect the flow rate, with the fastest flow where the bank is steepest and the slowest flow where the bank slopes gently down.
Other factors that affect stream water velocity are the size of sediments on the stream bed, as large particles will tend to slow the flow more than small ones. During a flood, the water level will rise so there is more cross sectional area for the water to flow in. If the river remains confined to a channel, the velocity of the water flow will increase but if the river tops its banks the water flow will decrease as there is more surface area for the water to move along.
Erosion prevention
There are a number of methods that municipalities can use stabilize banks and shoreline, from hard engineering techniques to simple restoration of natural vegetation. All of these methods are intended to protect water quality and in some cases preserve the integrity of the shoreline and safety of people and wild life.
Hard Engineering techniques
These techniques can be more expensive however have the advantage that they are more permanent and last longer so can be more cost effective where shoreline erosion is a concern. They include”
- Retaining walls
- Stone riprap
- Gabion walls and baskets
- Articulated concrete revetment mats
- Geotextile tubes, and
- Biologs
Soft Engineering Techniques
Soft engineering offers a different, more natural approach to preventing the erosion of riverbanks and shorelines. Soft engineering techniques offer advantages over traditional methods that have less respect and compatibility with nature. The concept behind soft engineering is the use of plant material as well as other natural materials to secure soil in place and prevent further erosion.
Other advantages to soft engineering is to increase biodiversity, increase the aesthetic value and to act as a filtration system that helps purify runoff water before it can enter the stream at full concentration. Soft engineering techniques are normally lower cost and are often used with other engineering techniques to provide a natural, effective, visually appealing and inexpensive solution to stabilizing riverbanks and shorelines. Some soft engineering techniques include:
Live Stakes - planting a woody cutting into the ground to develop an intricate root system over time and bind the soil.
Live Fascines - a long bundle of woody vegetation that is buried within a shallow trench running parallel to the flow of a river.
Brushlayers - a little different from live fascines in that instead of planting the roots vertically into the bank, they are planted horizontally into the bank.
Live soft gabions, also known as vegetated geogrids, use non-living material inconjuction with living material to stablilize a slope.
Brush Mattresses - are a natural solution that contain a layer of interwoven live branches that are planted to the mattresses by wire and live stakes placed along the eroding bank.
Live Crib walls - are a hollow three-dimensional structure constructed with treated timbers that act as a retaining wall which is then filled with soil and plant material.
Logging Requirements:
Rules:
As you float or paddle along the Credit River in your preferred watercraft, make some observations at the posted location, as well as the two additional waypoints. Take photos if you need to help you remember however do not post any spoiler photos on the cache page.
All observations can be made from the water and there is no need to step out of your watercraft.
For large groups, one person can submit the answers on behalf of the group. Please include the names of ALL geocaches in your party.
Questions
Posted Coordinates:
1. Based on the description, what hard engineering technique has been used at this location?
2. What is the height of the engineering technique, and is it high enough to prevent shoreline erosion at this location? ( Hint: Look for signs that the water level has reached the top or higher of this engineering technique
3. What is the approximate length of this engineering technique? Do you think it needs to be this length, shorter or longer?
4. Has the introduction of vegetation been added at this location to increase shoreline stability?
Waypoint # 2
5. At the second waypoint you will find a different hard engineering technique has been used on the outside bank. Based on the information on the cache page, what technique has been applied here?
6. What is the approximate height of this technique?
7. Has the introduction of vegetation been added or allowed to take root at this location to increase shoreline stability?
Waypoint # 3
8. Look at the shoreline just past and on the same side as the second waypoint. Do you see any form of erosion and if so, based on the types of erosion by water listed on the cache page, what type or types do you see at this location?
9. Based on your observations, do you believe that this erosion will likely increase or decrease over time?
10. Based on your observations, which of the hard or soft engineering techniques described in the cache page would you recommend to prevent further erosion?
References:
https://cvc.ca/wp-content/uploads/2011/07/Executive-Summary-Credit-River-Water-Management-Strategy-Update.pdf
https://opentextbc.ca/geology/chapter/13-3-stream-erosion-and-deposition/
