El(Bow) Rivers EarthCache

PLEASE NOTE: this cache is NOT AVAILABLE after a snowfall / when there's been significant snow / when it's frozen. You MUST be able to see the river flow and embankments to complete this cache. THIS IS NOT A NIGHT CACHE. 

Special tool required: internet/wifi access would be helpful

Please send your responses via the in-game IM system. I will read and reply to all responses. When confirmation is received, don't forget to post the required photo with your online log. Any responses appearing to be "arm chair" answers (or answers that are incomplete / missing) will not be acceptable; the point of an EC is to visit the site in person and learn something about the local geology/geography.

If working as a team, each person must post their own photo and the caching names of participants must be included by the person who is submitting the answers.

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A walk along the paved Bow River trail with some nice views. As you view the Bow River, you will explore erosion prevention methods. 

Note: the distance is 2.0 km from GZ to WP1 which is a 25 minute walk (paved path/bike trail).

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Why does Flooding Happen in Calgary?

The Bow and Elbow Rivers can look very different throughout the year. 

River levels generally rise every spring. Normal spring time flows can range between 70-400 m³/s on the Bow River and 15-80 m³/s on the Elbow River. Then beginning in mid-July we see them slowly go back down towards their winter levels. Each year flows will be different, based on the amount of snowmelt and rain. See Historical Data on River Flow Rates​.

Most of the time, a river is large enough to contain its flow within its banks. But if flows are high enough, the river can’t hold all the water, and it flows over normally dry land, through the floodplain.

Calgary experiences two types of flooding: river flooding and local stormwater flooding. River flooding tends to happen in the spring due to heavy rainfall in the mountains and foothills combined with snow melt which drains into our rivers. Flooding happens quickly and with little warning because of the short, steep distance the rivers travel from the mountains to Calgary.  Rivers and creeks can overflow their banks when full of rain water and snowmelt. This is called “overland flooding”. High river levels may also cause groundwater to rise and storm or sanitary sewer system backups that can flood basements. Local stormwater flooding tends to happen in the summer due to thunderstorms over Calgary. This causes pooling and stormwater drainage issues. If the rain is so intense that the stormwater system is overwhelmed, water may flow onto private properties. This is sometimes called “overland flooding”.

For further information, click here.

Erosion

There are a number of natural forces that lead to erosion including wind erosion, frost action, soil creep and slumping, but the most common and powerful source is water. As a river's velocity increases, so too does the amount of erosion taking place. There are four ways that a river erodes; hydraulic action, corrosion, corrosion and attrition.

Hydraulic action – the force of the water wearing away the bed and bank of the river

Corrosion – the chemical reaction between the water and the bed and bank of the river, wearing it away.

Corrasion/abrasion – where bedload in the river wears away its bed and bank.

Attrition – where rocks in the water become smaller and rounder by hitting each other.

River bank erosion occurs when water wears away at the banks of a river or stream. While river erosion is a naturally occurring process, human impact can increase its rate. Common contributing factors to river and stream bank erosion include:

• Clearing vegetation away from the river bank.
• Flooding.
• Intense rainfall.
• River bank saturation from nonriver water.
• Stream and land use management.
• River straightening.
• River redirection around infrastructure or debris in the channel.
• Characteristics of the river bank soil.

Other forms of erosion include:

Soil Creep: Soil creep defines the slow mass wasting process of soil on a slope, under the influence of gravity.

Slumping: A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a slope. Movement is characterized by sliding along a concave-upward or planar surface.

Ice:  Cycles of freezing and melting push ice onto the shoreline.  Ice can cause significant shoreline damage.

Storm water:  Storms remove or displace loose layers of soil causing sheet erosion.

Sheet erosion: Sheet erosion occurs as a shallow 'sheet' of water flowing over the ground surface, resulting in the removal of a uniform layer of soil from the soil surface. Sheet erosion occurs when rainfall intensity is greater than infiltration (sometimes due to crusting). Rarely seen but accounts for large volumes of soil loss.

Erosion Prevention Methods

• Revetments: an engineering technique used on a sloping surface or creating a sloping surface using stone, concrete or other material that creates a slope to absorb the energy of incoming water (click here);
• Rock armour/riprap: large boulders placed in front of a cliff or slope to deflect (wave) energy away and protect the shoreline from erosion (click here);
• Gabions: a cage-like structure filled with rocks or concrete (click here).
• Tree revetment is a river bank erosion control system that uses small fallen trees anchored horizontally in place along the river bank to prevent erosion. The trees slow the flow of water, which cuts back on the rate of erosion. They also catch sediment in the tree branches and prevent it from flowing down the river.
• Coir logs are another river bank erosion repair method made using coconut fiber. Coir logs are large in diameter, which makes them ideal for supporting river banks or being used for erosion control on hills, shorelines, and other areas prone to erosion. Even though they’re big, coir logs are easy to place. Once they’re in position, they can help establish vegetation growth. They’ve been effectively used in construction sites, restoration projects, and stabilization areas. Most coir logs will last two to five years before biodegrading. (click here)
• Natural vegetation has a major impact on bank erosion. For the most part, river banks that have vegetation erode slower than those without. This is because the roots of the vegetation generally increase the soil’s strength around the river bank, which makes the bank less prone to mass failure. Additionally, plants can act as shock absorbers during heavy rainfall, which also slows the rate of erosion.
• Soil erosion mat: While these mats are sometimes made with wood fiber or straw, one of the top materials used is coir coconut fiber. This is because coir is strong yet natural. Plus, unlike straw or wood, coir can last in the water anywhere from two to five years. (click here for an image)

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Questions:

1. Post a photo of you/your GPS/your caching name at GZ with the (cement) bridge to Prince's Island clearly visible. NO spoilers of the Bow River, please.

2. Look at the Bow River (at GZ and WP1). Based on the cache lesson, what types of erosion have likely occurred and why?

3. Based on the cache lesson, what erosion prevention methods are in place?

4. Describe how effective you believe these methods to be. Provide evidence from your observation of GZ.

Optional: walk (drive) down to the Mission Bridge (WP2) and note any similarities/differences in the Elbow River environment.

Enjoy! I look forward to reading your responses. IF you are delayed in sending your answers, please post a note until you are able to send me your answers. I reply to all answers sent.