~~ Welcome to the Dam Earthcache ~~
~~ on the St. Joseph River! ~~
( THIS IS NOT A QUICK EARTHCACHE )
(Please read the whole cache page)
*** This Earthcache can be done via land or sea!
In this case, it would be easier in a watercraft.
Use your best judgment, safe travels and Happy Floating! ***
- As this is an Earthcache, there is no physical container at any of the locations.
- Answer the quesitons below to log this cache!
There are 190 dams in the St. Joseph River watershed, and 17 on the river mainstem.
This Earthcache will take you to TWO of them.
Definition:
Dam: a barrier constructed to hold back water and raise its level, forming a reservoir used to generate electricity or as a water supply.
For this earthcache, we will explore dam erosion & flow rates.
We will be comparing TWO dams and their similarities and differences.
Dam #1 - Union Lake Dam (Riley Dam) POSTED COORDS
Dam #2 - Sturgis Dam REFERENCE WAYPOINT - about 20 miles downstream (28 min drive)
YOU MUST VISIT BOTH DAMS.
EROSION
Here's a more detailed explanation of the erosion process after a dam:
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Sediment Deposition and Starvation:
Dams create reservoirs that trap sediment, leading to a downstream "sediment starvation" where the river lacks the materials it needs to build and maintain its channel and floodplain.
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Release of Sediment:
When a dam is removed or water is released, the stored sediment is released downstream, causing a temporary increase in the river's sediment load.
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Increased Erosion:
The sudden influx of sediment can lead to increased erosion of riverbanks and the riverbed as the river adjusts to the new sediment load and flow conditions.
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Channel Instability:
The increased erosion can cause channel instability, leading to changes in the river's path, depth, and width.
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Erosion Types:
- Bank Erosion: The river's banks can erode as the increased water flow and sediment load destabilize them.
- Bed Erosion: The riverbed can erode as the increased sediment load and flow scour the channel.
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Internal Erosion:
Water seeping through cracks, joints, and fissures in the dam or its foundation can erode the concrete or soil, potentially leading to severe damage or failure.
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Overtopping Failures:
Uncontrolled flow of water over, around, and adjacent to the dam can cause erosion, especially in earth embankments which are not designed to be overtopped.
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Vegetation and Erosion:
Lack of vegetation on dam slopes and spillways can lead to erosion, and livestock grazing on dams can also contribute to erosion.
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Long-Term Effects:
While the initial phase of erosion can be significant, rivers often have the capacity to recover and stabilize their channels over time, with the degree of sedimentation depending on factors like sediment volume, river geomorphology, and sediment management plans.
Here's a more detailed explanation of the flow rate implications at these sites:
Dams significantly alter natural river flow regimes, leading to reduced peak flows, increased low flows, and changes in flow timing and periodicity, which can have profound impacts on erosion, aquatic ecosystems and downstream water resources.
Here's a more detailed explanation of the flow rate implications after a dam:
- Altered Flow Regimes:
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Reduced Peak Flows:
Dams store water, reducing the frequency, magnitude, and duration of high flow events (floods) downstream.
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Increased Low Flows:
Dams can also increase the frequency, magnitude, and duration of low flow events, potentially leading to water scarcity and habitat degradation.
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Changes in Timing and Periodicity:
Dams can alter the natural timing of high and low flows, which can disrupt ecological processes and the life cycles of aquatic organisms.
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Stabilized Flow:
Dams with regulated releases can stabilize water flow, thus reducing variability, which can be beneficial in some cases, but also detrimental to certain species that rely on natural flow fluctuations.
How to Access Both Dams:
Since, you must visit BOTH dams to observe and infere, I have included waypoints to make your journey easier.
(Yes, both dams are a requirement, not just one and done)
LOGGING REQUIREMENTS
Please complete the tasks and questions below, and send me your answers. If logging for a group, please include the names of everyone in your group. This ONLY applies to task 1 & 2.
(1) Erosion:
(A) - How does water release from a dam affect downstream erosion? Do you think the release at each site was uniform or uneven?
(B) - How did the dam size(height&width) affect the erosion downstream? Which one controlled erosion better?
(C) - Do you see any signs of erosion at either dam along the river banks or further downstream? Describe where and what you discovered.
(D) - Do the river banks at each dam have vegetation or is it just sediment, sand and rocks from the churning water?
(E) - Did you see any of these types of erosion at either site? Bank Erosion, Bed Erosion or Internal Erosion? (Yes or no for each type & location)
(2) Flow:
(A) Calculate the flow rate in "Feet Per Second" for EACH of the two river sections after the dam (200 ft from the dam).
- This may be done by measuring a distance along each of the rivers banks, floating an object(a stick, leaf, floatation device on a rope or your watercraft) from your starting point to the ending point, and recording the time it takes to float the distance.
- Once the "Distance" and "Time" are determined, calculate the "Feet Per Second" for EACH section.
(B) Now do these times reflect your research on erosion of the river banks? Does the faster flow after a dam have more erosion at the edges? Does a controlled uniform flow provide more or less erosion at these sites? Note your observations, compare and contrast the differences.
(C) List the approximate width(water flow, not overall dam width) and flow distribution (e.g. uniform, more agressive on the sides, white caps etc.) of each dam.
(3) PHOTO: REQUIRED
Take a photo of yourself (or personal item) at BOTH dam locations showing EACH dam in the background. This is a requirement. Please attach it to your found it log.
ANY logs without BOTH photos will be automatically deleted immediately. Groundspeak allows this requirement as proof you actually visited the site(s).
If you need help or advice on completing this Earthcache, please message me. Hope you enjoyed this lesson. Happy travels!