Napa River Oxbow Earthcache EarthCache
Napa River Oxbow Earthcache
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As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
The cords take you to the parking lot for the new Oxbow Reserve. Access to the Preserve area is currently from McKenzie Drive on the Silverado Trail side. In the future, the Napa River Trail will connect to the Preserve, linking this peninsula to what will be a contiguous 6-mile trail. The vision also includes a future project to provide a pedestrian bridge, spanning the River from the west to the Preserve.
The Oxbow is most visible to the left on/ near the trail.
The Napa River is not losing elevation very quickly. In fact, there is less than 17’ of elevation drop in the last 30 miles of the Napa River flow. Thus, water that at one time was rushing downhill from creek watersheds into the Napa River slows and begins to meander. In these areas of low slope (elevation not dropping very quickly), the path of the river begins to wander back and forth creating meanders, or curves. Along each curve, the flow of the river is constantly eroding the outside bank of the meander, while at the same time depositing material on the inside. This is because the area of fastest flow in the river is forced to the outside bank on the curves and the slowest flow is on the inside. Faster water carries more sediment causing the erosion. The slower water is unable to carry as much sediment, so some sediment drops out of the water. The result is a steep bank on the outer edge of a meander and a gentle slope on the inner edge.
Over time, these meanders get larger more pronounced as the outer edge is eroded away and the inner edge has material deposited on it. Given enough time, the pronounced oxbow meander you see in front of you could get so curvy that it bends back and touches itself creating an oxbow lake (and this land would then be an island).
An animation of river meander formation can be found at (visit link)
Coordinates #2 N 38 18.298 W122 16.840: These cords show extreme erosion, and several feet of the bank have been eroded by the pronounced meander in the bend. You’ll need to make an observation from this point for logging requirements.
Logging Requirements:
Send the answers to #1-#5 to me through my geocaching profile.
1. List the name “GC20WYR Napa River Oxbow Earthcache” in the first line of your email. Also, list the number of people in your group.
2. How many feet back upstream has the river eroded the eastern edge of the river? If the following formula is approximately correct, how many years until the erosion makes the park an island? ( just over 2 feet per year averaged over 10 years).
3. If eventually this park becomes an island, what other effects do you envision the “straightened river” having on the area?
4. How many acres comprise this oxbow park? (see interpretative sign)
5. (Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Post a picture of yourself and your GPS with your log at the 2ndary cords (with the oxbow in the background. DO NOT show any of the pertinent information in your picture or your log may be deleted.
Resources:
Napa Water Management District. Information brochures, Napa River Restoration Project 2006.
Additional Hints
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