While geocaching in the area, I noticed several signs underneath the Aurora Bridge near Geocaching HQ. As I looked even closer, I discovered that there was meticulous planning by the City of Seattle to create a bioswale that leads up to the Fremont Troll to Union Lake.
Bioswales are becoming more common in urban areas as they provide local streams and rivers a natural way to filter out runoff and other pollutants in addition to reduce flooding and erosion during storms.
The Lake Union Watershed contributes roughly 900 billions gallons of water to Lake Union. Most if not all of this water is contaminated both with artificial pollutants, but also particulates from erosion of the landscape. The green line in the image below is the location of the Fremont Bioswale, which was created to help improve erosion as well as a natural way to artificially treat water before it enters Lake Union.
"The bridge’s runoff at this site impacts a critical migration route for salmon on their trip out to the Pacific Ocean as well as their return trip to the upper watershed spawning grounds." -- from 700 million gallons dot org, who provided a case study on the environmental and geological impact of the Fremont bioswale.
Urban areas have limited natural runoff located due to the amount of asphalt and concretes involved in creating streets and sidewalks. A bioswale acts as an artificial filter which prevents pollutants from entering local waterways as well as managing errosion and preventing it from occuring in large ammounts. There are several ways this can be done, first of which involves directing runoff sources to the designated bioswale area.
This part of Seattle is very hilly (image above showing elevations in the city) and thus it is simple to direct runoff from neighboring streets to the area below Aurora Bridge. Second, within the bioswale there are native plant species which have three added benefits. They encourage local fauna by providing a natural habitat, their root systems hold in soils and prevent erosion (which can cause damage to infrastructure if not maintained properly), and they can filter particulates from the water as it seems through the soil that the plants are holding in place.
And third, adding larger barriers to prevent trash from entering the watershed in large storm events. Here, the city has installed gabion spillways within the bioswale. A gabion is a metal cage filled with rocks which allow water to seep through in high amounts, without allowing trash and large items to pass through. In large storm events, trash entering waterways is of particular concern. These spillways prevent this from occurring.
There are four main types of transportation of materials (erosion). The first is suspension which is like sand that is being suspended in the later. The next is solution which is dissolved minerals on the atomic scale like salt. The next two are traction and saltation which are big enough to see from afar.
Traction are large boulders which are moved only during large flooding events, while saltation are smaller rocks and pebbles which are moved periodically. The way you can tell the difference between tractions and saltations are their textures. Tractions, only being moved in floods, are quite jagged and rough to touch. On the other hand, saltations are smooth and round as they have bounced down stream frequently.
https://www.geocaching.com/geocache/GC720TN_waterfront-trail-series-ajax-bioswale
https://www.geocaching.com/geocache/GC5X4V8_newport-boulevard-bioswale
http://dudek.com/services/stormwater-planning-and-design/
http://chubbyrevision.weebly.com/river-landforms.html
https://700milliongallons.org/case_study/fremont-bioswale-project/
https://cleanlakeunion.org/get-a-clu/
https://www.floodmap.net/Elevation/ElevationMap/?gi=5809844
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
Note: You will only receive an email from me if I need clarification on your answers. You are free to log the cache as a find whenever you like.
1. "Fremont Bioswale" on the first line of your email AND list all geocaching names of your party so I can match your answers to them.
2. Take a photo of you (or your signature item if you don't want to show your face) with the bioswale in the background at the posted coordinates. Each log MUST have a unique photo attached. No sharing photos allowed!
3. Look at the bioswale and determine if there is any water flow. If so, estimate the velocity (how fast it's moving). If not, where is it collection or non-exisitant?
4. Name at least one type of erosion transportation materials that you can see. Explain why you can see it here and why you can't see the others. Use the chart above to help you located them.
5. Estimate the (a) width AND (b) depth of the bioswale. Does this answer change as you walk up (northward) towards the Fremont Troll?
6. As you walk up the hill towards the Fremont Troll (northward), how many gabions are located here?
7. Out of all the errosion prevention techniques, which one do you think is (a) most and (b) least effective? Explain your answer based on your observations.