This earthcache may not be possible to complete during periods of extreme rainfall due to flooding of the park.
Viewed from above, the pond in Fishtrap Creek Park. This is no ordinary pond; this is a specially constructed stormwater storage basin (or retention pond). Its purpose is to give surface runoff from the nearby neighbourhood a place to go, and to clean that water before it enters Fishtrap Creek, to the southwest.
A retention pond, sometimes called a wet pond, wet detention basin, or stormwater management pond (SWMP), is an artificial pond with vegetation around the perimeter, and includes a permanent pool of water in its design. It is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or, bay.
In undeveloped areas such as forests and grasslands, rainfall and snowmelt collect and are stored on vegetation, in the soil column, or in surface depressions. When this storage capacity is filled, runoff flows slowly through soil as subsurface flow. In contrast, urban areas, where much of the land surface is covered by roads and buildings, have less capacity to store rainfall and snowmelt. Construction of roads and buildings often involves removing vegetation, soil, and depressions from the land surface. The permeable soil is replaced by impermeable surfaces such as roads, roofs, parking lots, and sidewalks that store little water, reduce infiltration of water into the ground, and accelerate runoff to ditches and streams.
Stormwater refers to rainfall and other surface runoff, and the journey it takes between falling from the sky and entering a river or lake.
Stormwater ponds are an example of an “end-of-pipe measure”. They receive stormwater runoff through the sewer system and store it for a time, to allow sediment, debris, and contaminants to settle before the water enters a natural waterway. The controlled release of the stormwater also helps prevent flooding and erosion. Stormwater ponds, like this one, are permanent wetlands. They always contain a minimum volume of water, which fluctuates as stormwater pours in from the sewers and then empties into the downstream waterway. The water must reach a certain depth in order to pass through the outlet, ensuring there will always be enough water to sustain the wetland habitat.
As stormwater moves overland and through the sewer system, it picks up sediments, debris, and contaminants and transports them toward the stormwater pond. The ability of water to transport various particles depends on the velocity of the water and the size of the particles. Water flows fastest when confined to a narrow channel or when flowing downhill, and slowest when it has room to spread out laterally or when there is little elevation change. The faster the flow, the larger the particles the water can carry. Stormwater ponds serve as locations where the fast-flowing stormwater can spread out and slow down, causing the particles to settle to the bottom. The longer the water remains stored in the pond, the more sediments, debris, and contaminants will settle, cleaning the water before it exits through the outlet.
Sources
https://www.abbotsford.ca/city-services/dyking-drainage
https://en.wikipedia.org/wiki/Retention_basin
To log this earthcache as found, first e-mail or message me the answers to the questions (don’t post them in your log!). You may then log it as found (with the mandatory photo) without hearing a response from me.
Questions/Tasks
1. If a retention pond like the one before you holds onto water without releasing it until it overflows, what added benefit does it provide in terms of solid contaminants / sediments? (answer on cache page)?
2. While standing on the structure you will notice obstacles (think BIG) are present within the pond, what benefit do you think this has for the pond (think how they could affect the flow of water)?
3. What is another name for a retention pond?
4. (Mandatory) Post a photo of yourself on the structure at the posted coordinates (a hand giving a thumbs up is fine if you don't want to show your face)