Agent H2O EarthCache
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Two Rivers Park--behind the Ruidoso Valley Chamber and Visitor’s Center --700 block of Sudderth Dr., Ruidoso, New Mexico. Sudderth Dr.is the main street (Highway 48) that runs through the center of the village of Ruidoso. Park at the east end paved lot.
In this EarthCache you will be looking at a riverbed and determining what type(s) of sediment load has been deposited/transported in the past. You will also be comparing current steam speed and discharge to possible past speed and discharge amount and determining what classification sizes of sediment are present. A metric measuring device (ruler or tape measure) is needed to accomplish this task.
Running water is the most affective of all erosion agents. Running water wears down the land in two ways. It breaks up the bedrock over which it flows. Using sand, pebbles, even boulders as cutting tools, as it grinds and hammers away at its bed. The carrying power of a stream is indicated by both the total amount of sediment in the stream and by the size of the particles being moved by the stream.
The carrying power depends upon the speed of the stream and its discharge. Stream discharge is the volume of water flowing past a given point in the stream at a given time. The carrying power of a stream increases as the speed and discharge of the stream increase.
When particles are eroded and transported by wind, water, or ice, they become part of the transport medium's sediment load. There are three categories of load that may be transported by an erosion agent: dissolved load, suspended load, and bedload.
Sediments come in all shapes and sizes. Sediment sizes are classified by separating them into a number of groups, based on metric measurements, and naming them using common terms and size modifiers.
The terms, in order of decreasing size:
boulder (>256 mm)
cobble (256–64 mm)
pebble (64–2 mm)
sand (2-1/16 mm)
silt (1/16–1/256 mm)
clay (less than 1/256 mm)
Pebbles and boulders, etc., that are too heavy to be carried in suspension, are carried in a bed load, especially during floods. Geologists estimate that the rivers of the United States carry 25% of their load in solution, 50% in suspension, and another 25% in the bed load.
Start at the parking lot at the east end of the park.
Stage 2 coordinates should give you an idea of how this park got its name.
If you have followed the coordinates correctly, Stage 3 coordinates have placed you at the center of a metal bridge spanning the river. If necessary return to these coordinates. Determine the answers the log questions below:
1. From the center of the bridge, look upstream. Then look downstream. Judging by the condition of the banks of the river and the bed that is visible, which area, upstream or downstream is least affected by erosion?
2. Which portion is most affected by changes caused by more carrying power due to increases in speed and discharge?
3. Which size classification of sediment is more noticeable?
To continue the cache, be sure to cross over the bridge. Stage 4 coordinates show a problem area. To complete the cache, find answers to these last 2 questions:
4. Measure and name 4 size classifications of sediments.
5. Considering the largest sized sediment you measured, what can you determine about the speed of the river’s discharge in the past?
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