What is Erosion?
Erosion is when rock and soil is removed from the Earth’s crust and moved to a different location. There are 5 main types of Erosion:
1. Erosion due to water
2. Erosion due to wind
3. Erosion due to gravity
4. Erosion due to soil
5. Erosion due to ice
WATER EROSION - from rain or another source exposes water-sensitive areas which can decay, or the force of very hard droplets which can also erode hard sedimentary surfaces. As water builds up run off picks up soil exposing roots and rock underneath which can lead to destabilization of the surrounding soil.
WIND EROSION - Excessive amounts of wind can cause top soil or sand to be blown away and expose other soils and rock underneath.
GRAVITY EROSION - Mass movement of soil occurs on steep slopes under the influence of gravity. The process involves the transfer of slope forming materials from higher grounds due to its own weight.
SOIL EROSION - A result of gravity pushing down on soil that may rest on hills, as well as water, wind and glacial melting, which can cause soil to wash away and tree roots to be exposed. [1]
EROSION DUE to ICE - Snow and ice will melt causing water to run down hills and mountains - this water has the tendency to cause stream-ways and ditches. [1]
The Fox River has had numerous flooding episodes and the city of Geneva is actively using methods to prevent and eliminate erosion at this community park. The banks of the Fox River are made up of rocks, sand and clay, but as they erode, the plant life on the banks of the river are washed away. These native plants help prevent erosion naturally and keep the river bank healthy. Their deep roots hold the soil in place and filter water. They are adapted to riverbank conditions which reduces long-term maintenance. They increase the diversity of wildlife by providing food and homes. The city is using three different stabilization methods to provide immediate protection to the riverbank while many native plants are still young. They are using Lunkers, A-Jacks and Fiber Rolls. There is a sign at ground zero which provides visual descriptors of these stabilization methods for the geocachers reference.
Lunkers
Lunkers are crib-like, wooden structures installed along the toe of a river, stream or creek bank to create overhead bank cover and resting areas for fish. A lunker consists of two planks with wooden spacers nailed between them. Additional planks are nailed across the spacers perpendicular and a crib like structure is formed.
The structure is installed by first grading the riverbank back and creating a trench along the new bank line. This trench must be wide and deep enough so that the lunkers lay flat and are completely covered by water. The lunkers are secured to the stream bottom with rebar. Once in place, rock is placed on top of and behind the lunkers and the riverbank is graded down to meet the front edge of the lunker. The upper bank is then stabilized using bank stabilization techniques.
Lunkers were originally developed as habitat enhancement structures. As such, they have a significant potential to improve stream habitat in the form of undercut banks and overhead cover.
A-jacks
A-jacks are three two-foot long cement stakes joined at the middle (six one-foot legs). They are a commercially made concrete product, originally made much larger (10-foot legs) to serve as breakwaters along shore fronts. They have been in use in the Midwest for several years. They serve to add structural stability to the lower stream bank.
A-jacks are manufactured in two pieces each weighing 45 lbs and are assembled onsite. The first step in the installation is to excavate a shallow trench along the toe of the stream bank. The A-jacks are assembled and placed in a row(s) along the trench so that each a-jack is interconnected with its neighbor. Rock, geotextile material or coir fiber is placed in the voids between the legs, and the a-jacks are backfilled. The upper bank is then stabilized using other bank stabilization techniques.
A-jacks have a modest potential to improve stream habitat, similar to that of placed rock or boulder revetments.
Fiber Rolls
Fiber rolls are the other type of erosion control device. These are usually made of the same materials used in erosion control blankets but are rolled into large diameter “logs.” These logs can be made to just about any diameter and are usually incased in some kind of netting sewing into the desired shape. The purpose of these logs is to pool up and slow down water long enough for any sediment that is in the water to settle out. The three major materials used in fiber rolls are coconut fiber, rice wattle and wheat wattle. The concept behind the fiber roll is the same regardless of the material.
TO LOG THIS EARTHCACHE:
1) Visit this location and take a picture of you and/ or your team and post it with your log (optional).
2) Survey the area and report which methods of riverbank stabilization do you being used on the immediate east shore of the island?
3) Survey the area and report which method of riverbank stabilization is being used on the opposite shore of the east riverbank of the island?
4) What evidence do you see of either of these methods being effective or ineffective in preventing erosion? Why or why not?
5) What type of erosion(s) do you think are the most impactful at both the island and land to the east of the island?
6) Email me with the answers of questions #2-5 - Please do not include the answers in your log.
Please answer the questions correctly to be able to claim the smiley for this earthcache. I expect the required logging information for this earthcache to be sent to me within three days or the "Found It" log will be in jeopardy of deletion. Thanks!