Saco River EarthCache

ABOUT THIS EARTHCACHE

For this EarthCache, you will be visiting an area of the Saco River to make some observations about river bank erosion. There is parking available at the posted coordinates.

LOGGING REQUIREMENTS

In order to log this EarthCache, send me your answers to the following questions either through email or messaging from my profile page.

1a: What type of prevention, if any, is being used on the near side of the Saco River?

1b: If anything has been done, is it working? If nothing has been done, what could be done to make a difference?

2a: What type of prevention, if any, is being used on the far side of the Saco River?

2b: If anything has been done, is it working? If nothing has been done, what could be done to make a difference?

3: Give an example of erosion and what part of the banks you can see this.

4: Post a pic of you or a personal item with the bridge in the background.

If you enjoyed this EarthCache, please consider giving it a favorite point.

THE SACO RIVER

The Saco River is a river in northeastern New Hampshire and southwestern Maine in the United States. It drains a rural area of 1,703 square miles of forests and farmlands west and southwest of Portland, emptying into the Atlantic Ocean at Saco Bay, 136 miles from its source. It supplies drinking water to roughly 250,000 people in thirty-five towns; and historically provided transportation and water power encouraging development of the cities of Biddeford and Saco and the towns of Fryeburg and Hiram.

BANK EROSION

Bank erosion is the process by which soil and rock materials are removed from the banks of rivers due to the forces exerted by flowing water exceeding the bank's resistance, which is provided by soil cohesion and vegetation.

The energy of the river flow is the primary driver of erosion, and this energy varies across different river systems, along the length of a river, and seasonally. High-energy events, such as floods, significantly contribute to erosion by increasing the river's capacity to transport sediment and by destabilizing riverbanks. The rate at which eroded materials are transported downstream as part of the river's sediment load influences the exposure of riverbanks to further erosion, creating a dynamic and often discontinuous process.

PREVENTION

To prevent bank erosion, a combination of methods can be used, including vegetation, hard armoring, and engineered structures. Vegetation, particularly native plants, provides natural erosion control by stabilizing the soil with its roots and providing a buffer against water flow. Hard armoring, like riprap, can protect the bank from the force of water, while engineered structures like stream restoration structures can redirect flow and reduce erosion.

VEGETATION
Plant roots bind soil together, strengthening the bank and preventing erosion. The vegetation also provides shade, which can cool the water and protect aquatic life, and it can filter pollutants, improving water quality.

Riparian Vegetation
Establishing healthy riparian vegetation is a key strategy. This includes planting native willows, cottonwoods, shrubs, and trees to create a dense, complex habitat that can withstand erosion.
Vegetative Buffer Zones
Creating a buffer zone of vegetation along the bank can help slow down water flow, intercept sediment, and protect the bank from rain-impact erosion.

HARD ARMORING
Hard armoring is the construction or placement of vertical seawalls or bulkheads, sloped riprap (eg rocks) revetments, groins, jetties, or breakwaters along a shoreline.

Riprap
Placing rocks along the bank can help protect it from the force of water, reducing erosion.
Gabions
Using gabions (wire baskets filled with rocks) can also provide protection against erosion.
Other Hard Armoring
Other hard armoring techniques include concrete retaining walls, sheet piling, and soil-cement.

ENGINEERED STRUCTURES
An engineered structure is a construction that is designed and built based on engineering principles, using calculations and knowledge of materials and their behavior to ensure its stability and safety under expected loads.

Stream Restoration Structures
These structures, such as log vanes, cross vanes, or toe wood, can redirect flow and reduce erosion by creating a more stable channel.
Redirectional Bank Stabilization
This involves using barriers like groynes, spurs, or vanes to redirect flow and reduce the force of water on the eroding bank.
Longitudinal Peaked Stone Toe Protection (LPSTP)
A method developed by the US Army Corps of Engineers that uses a layer of rocks to protect the base of the bank.
Tree Revetment
Using small fallen trees anchored horizontally along the bank can slow water flow and catch sediment, promoting natural vegetation growth.

SOIL BIOENGINEERING
Soil bioengineering is a method that uses living plant materials to construct structures that provide both engineering and ecological functions, particularly for erosion control and slope stabilization.

Soil bioengineering
This approach combines revegetation with techniques like willow stakes and spiling to help plants become established before they are washed away.
Terracing
Creating terraces on steep banks can help to slow down water flow and reduce erosion.
Windrows and Trenches
These can be used to divert water flow and prevent it from reaching the eroding bank.

references