Yakima River Delta Earthcache EarthCache
Yakima River Delta Earthcache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This earthcache has been designed to be approached by water (kayak, canoe, or kayak are best) for the full experience but setup with an alternative short hike for you land lubbers. Please note either approach will likely need additional equipment to aid in meeting the requirements as noted below.
While the full experience requires a boat, the land experience will require binoculars (or use your camera zoom) to make the observation requirement at the cache location several hundred feet off shore. Either approach you will likely need to get a bit wet to fulfull the first requirement. As always please practice water safety.
To log a find you must email me the answers to the following questions. Once you have emailed me the answer please mark the cache as a find and if there are any problems with your answers you will hear back from me. If you would like to learn more about Earthcaches visit www.earthcache.org.
Email me your answers to the following:
1. Reach into the water and grab the sediment. Describe the composition of the sediment (silty, pebbles, small rocks, large rocks, fine, rough, etc.) and note which location you are at (land or water). Bonus: If you boating check out both areas and compare and contrast both.
2. Based on your location observation and aided by using the information about deltas below, describe why you think the type of sediment composition is found here.
3. Describe the object located at the posted Earthcache coordinates. Specifically what is the object? How did it come to get here? Estimate how much of the object is exposed above the water line (in feet)?
The Yakima River flows 215 miles from the outlet of Keechelus Lake in the central Washington Cascades southeasterly to here where it meets the Columbia River, draining an area of 6,155 square miles.
The Yakima River Delta is located in south Richland and is full of walking trails through wetlands and thick tree cover. It is fairly common to see a variety of birds including blue herons, ducks and other waterfowl, coyotes, otters, beaver, jack rabbits, bull frogs, and fish in the Delta.
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Over long periods of time, this deposition builds the characteristic geographic pattern of a river delta.
When the flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity, which diminishes the ability of the flow to transport sediment. As a result, sediment drops out of the flow and deposits. Over time, this single channel will build a deltaic lobe (such as the bird's-foot of the Mississippi delta), pushing its mouth further into the standing water.
As the deltaic lobe advances, the gradient of the river channel becomes lower because the river channel is longer but has the same change in elevation. As the slope of the river channel decreases, it becomes unstable for two reasons.
First, water under the force of gravity will tend to flow in the most direct course down slope. If the river breaches its natural levees (i.e., during a flood), it will spill out onto a new course with a shorter route to the ocean, thereby obtaining a more stable steeper slope.
Second, as its slope gets lower, the amount of sheer stress on the bed will decrease, which will result in deposition of sediment within the channel and a rise in the channel bed relative to the floodplain. This will make it easier for the river to breach its levees and cut a new channel that enters the body of standing water at a steeper slope. Often when the channel does this, some of its flow can remain in the abandoned channel. When these channel switching events occur a mature delta will gain a distributary network.
Another way in which these distributary networks may form is from the deposition of mouth bars (mid-channel sand and/or gravel bars at the mouth of a river). When this mid-channel bar is deposited at the mouth of a river, the flow is routed around it. This results in additional deposition on the upstream end of the mouth-bar, which splits the river into two distributary channels.
References
USGS Yakima River Basin Project - (visit link)
Slingerland, R. and N. D. Smith (1998), Necessary conditions for a meandering-river avulsion, Geology (Boulder), 26, 435–438.
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures