## Lesson Plan

### Overall Rating

Subject:
Earth Science, Hydrology, Mathematics
Duration:
45 minutes
Group Size:
Up to 24 (4-8 breakout groups)
Setting:
in the park
National/State Standards:
Keywords:
surge flow, medano creek

### Overview

Students will understand the globally rare phenomenon of surge flow, exhibited in Medano Creek. Students will conduct an experiment by measuring, recording, and graphing data about stream flow. Students will compare the waves of an ocean on the beach to the surges of water in Medano Creek. They will also use measuring skills to compare the pulses of water.

### Objective(s)

Students will understand the globally rare phenomenon of surge flow, exhibited in Medano Creek.

Students will conduct an experiment by measuring, recording, and graphing data about stream flow.

Students will compare the waves of an ocean on the beach to the surges of water in Medano Creek. They will also use measuring skills to compare the pulses of water.

### Background

Medano Creek exhibits a unique phenomenon, in that it flows in periodic surges like ocean waves coming onto the beach. For surge flow to occur, three conditions must be met: swift water velocity, shallow water depth, and a sandy streambed. Medano Creek meets all three criteria, as does Sand Creek on the other side of the dunefield. Medano Creek has a steep slope, as streams go, and as a result, the stream has a high velocity. It is also shallow and flows over a bed of almost pure sand. As the water flows, ridges and troughs (antidunes) of sand form on the floor of the creek. The troughs act as tiny dams holding the water back until the flow breaks over the top, causing a surge. New antidunes continually form and break.

Surge size and frequency depend on how much water is flowing in Medano Creek. In the spring and early summer, the average frequency occurs approximately every 15 seconds. The students will test to see if the surges really do come every 15 seconds.

In normal precipitation years, these experiments are best conducted during spring and early summer, when Medano Creek is flowing. This is a seasonal creek that typically stops flowing past the main dunes access area from midsummer through early spring. Visit Great Sand Dunes' web page on Medano Creek for the season's flow forecast and current creek conditions. Note that creek flow is highest and surge flow is strongest at sunrise each day; it is lowest and weakest in late afternoon.

### Materials

stop watches,clipboards, paper, pencil, colored pencils, yardsticks, Surge Flow Graphing Worksheet (PDF)

### Assessment

Has anyone ever been to a beach by an ocean or lake? How are the waves and surrounding environment similar and/or different from what students are seeing along Medano Creek?

### Vocabulary

antidune, bore, hydrology, flow