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One Day, One Bend, Two Million Years: How the Sable River Shapes Its Valley

Grade 7 earth science: a river cleanup club uses bank stakes, sediment data, an oxbow cutoff and valley depth to explain processes at different scales.

Grade 7ScienceInteractive · Printable

Aligned toMS-ESS2-2

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
11 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Sorting, Short answer

About this worksheet

What students practice

Students analyze bank and sediment data to describe how a river wears away and builds up land.
Students compare processes that take hours, years and millions of years and that change a bend or a whole valley.

How to use

Before students start, have them sketch a river bend and label the outer bank and the inner bar from paragraph 2; the time-scale sort works well as a pair discussion.

Curriculum

NGSS standard covered

MS-ESS2-2

Explain how geoscience processes at very different time and size scales have changed Earth's surface.

Preview

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One Day, One Bend, Two Million Years: How the Sable River Shapes Its Valley

Use river cleanup measurements to explain how fast and slow processes at different sizes change the land.

Heron Bend

Read the passage and study Table 1. Then answer the questions.

What the River Keepers Measured

1Every October since 2016, the River Keepers club at Hollins Middle School has spent a Saturday pulling trash out of the Sable River. The club works along a 3 km stretch where the river winds back and forth across a wide valley floor in big loops called meanders. County hydrologist Mr. Anatoly Brandt joins them each year and has the students help him take measurements.

2At Heron Bend, the river curves sharply. On the outside of the curve, the water runs fast and deep against a steep bank of sand and gravel, and a few trees topple into the river every year. In 2016, Mr. Brandt drove a steel stake into the ground behind the outer bank. Each October the students measure from the stake to the edge of the bank. On the inside of the curve, where the water is slow and shallow, a low bar of sand and gravel slopes into the river, and the students measure its width too (Table 1). In 2023, while digging out a tangle of fishing line, volunteers found a plastic bottle stamped 2019 buried 50 cm deep in the inner bar.

3Downstream, Fox Bend used to be a long loop around a narrow neck of land only 30 m wide. In May 2019, after three days of heavy rain, the river rose 4 m and floodwater poured straight across the neck. In less than a day it cut a new channel there. The old 1.2 km loop was left behind as a curved lake, now called Fox Oxbow.

4During that flood, the gauge at the Route 9 bridge recorded far more sediment than usual (Table 2). Mr. Brandt estimates that the river carries about 25,000 metric tons (t) of sediment past the bridge in an average year.

5The valley itself is about 100 m deep where it cuts through sandstone hills. Under the valley floor, a few meters of sand and gravel lie on solid sandstone. Geologists estimate that the river has been cutting the valley down into the sandstone for about 2 million years.