Redmond Rain #19 - Willows Creek Traditional Cache
Hidden : 8/4/2018
Difficulty:
2 out of 5
Terrain:
3.5 out of 5

Size: Size: large (large)

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Geocache Description:



Redmond Rain can move mountains!


Features: steep slopes, vegetation, falling trees, and maybe some rain. Thanks for your CITO!

FTF: dugfresh


Pay attention as you make your way from the trailhead to GZ. To your left is a valley of thorns, nettles and mud. To your right is near vertical slopes. In the midst of it all are trees falling down the oversteepened slope. On a dry day, you can get from the trailhead to GZ in 20 minutes. On a wet day you may find yourself slip sliding away. Not recommended in stormy weather.

This cache was originally posted as a multi-cache in 2015. The posted coordinates for that multi-cache were the outfall described below. That area has been overgrown to the point that it is no longer suitable for a visit. As you skirt the worst of the vegetation, remember the ten intrepid visitors to the original 4T cache who wandered down into that valley to get what they needed to calculate GZ.

Leaning Trees


Keep your eyes open for leaning trees or other dangers or obstacles. Your are responsible for your own safety.



Parking


Recommended parking locations are noted. Please don't park in the maintenance access areas or try to cross streets at dangerous locations. The short walk on the sidewalk from recommended parking is the easy part of this cache. On your way from the reference point to ground zero, you're better off skirting the hillside until you are below the cache and then work your way up. When you leave, don't be tempted to find a way up through yards. As you leave the woods, you'll find yourself on private property with no trail or other access. Instead, just head back the way you came.

Willows Creek Erosion


When Redmond Way was constructed as Washington State Secondary Highway 2D in the 1950's, stormwater from 40 acres of development was released at the top of a high slope through an 18-inch corrugated metal pipe.



In late 2003, City staff learned that beyond the blackberries on the hillside below Redmond Way was a dramatic, failing slope. A hole had formed under the end of the pipe and had ultimately swallowed the pipe. The image above shows a 20 foot long stick of that pipe leaning against the side of that hole. Caution tape was placed above the slope and the City began seeking permits and funding for a repair.



The oversteepened slope was made up of very fine sand, interbedded with finer silts. The slopes are OK until they are exposed to weather, but with water flowing at the base of the slope, the slope was easily undercut and would periodically cause failure of a huge column of soil. The new pile of soil was then quickly carried away by the stream. This oversteepened bank presented a safety risk to anyone who might have been walking through the woods, maybe geocaching. Watch that first step!

To make matters worse, this failing slope was just 12 feet from PSE power poles. The loose anchor cables from those poles can be seen dangling over the slope in the picture above. To the west of this eroding hillside is the Olympic Pipeline gas line. And, of course, the high traffic Redmond Way is just a short distance south and up the hill, too.

Diversion



In 2005, an emergency repair project diverted the flows from the pipe through a temporary HDPE (plastic) pipe to the toe of the slope. This emergency action slowed the erosion by removing the primary cause, but left the steep slope to continue to weather and erode. The temporary outfall would work for a while, but a more permanent fix was needed. To save money, most of the temporary pipe was used in construction of the final outfall to the gabions.

Slope Stabilization



Following design and permitting, the City repaired the slope and constructed a new stormwater outfall. The first step was clearing away the blackberries and regrading the slope.

Fill the Hole



Next, more soil was placed to create a stable buttress to hold the slope in place.

Gabion Erosion Control



The new pipe outfall was constructed to discharge into a structure of rock filled wire "gabion" baskets that would reduce the energy from the water and limit erosion downstream. The water's energy is further reduced because the pipe outfall is mostly underwater all the time.

Topsoil



Next, topsoil was placed above the buttress material to make a good substrate for new plants.

Planting (Bioengineering)



Finally, tiny plants were planted all across the slope. Their roots would some day take hold and form the real stability for this hillside. Several years later, and plants have really taken hold of the slope. Looking at it today, it is hard to imagine the failure that took place so long ago.

You may notice trees cut down under the power lines high above. Puget Sound Energy routinely trims or removes trees to protect the power lines. This is really bad for the stream, and contributes to slope instability in places like this, but is part of the price we pay for having the power we need in our urban environment.

Question

After seeing what water can do to a hillside, would you want your house as close to the steep slope as some of these houses?

Additional Hints (Decrypt)

Nccebnpu guerr ynetr gerrf sebz orybj gb svaq n cynpr gb uvqr n Ynetr. Frr fcbvyre cubgb.

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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