# Drainage Basin Morphometry

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Initial Publication Date: July 16, 2008 | Reviewed: November 3, 2013

#### Summary

This is a map-based activity in which students will delineate a drainage basin and its channel network, use the "Strahler system" to order the channel network, and develop simple equations to describe the inherent organization within the watershed.

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## Context

#### Audience

undergraduate (junior-level) course in geomorphology for geoscience majors.

#### Skills and concepts that students must have mastered

1. use of the "contour-crenulation method" to delineate a drainage network
2. use of a map scale to measure distances on a topographic map
3. plotting data on x-y graphs, including semi-log and log-log formats
4. drawing best-fit lines through plotted data points
5. using a scientific calculator to perform simple regressions

#### How the activity is situated in the course

stand-alone exercise

## Goals

#### Content/concepts goals for this activity

The goal of this activity is for to students to observe and quantify the inherent organization within the channel network of a single drainage basin (a la Horton, 1945).

#### Higher order thinking skills goals for this activity

The higher-order skills developed by completion of this exercise include analysis of topographic maps and the development of mathematical models (equations) that describe the relationships among various basin attributes and stream order.

#### Other skills goals for this activity

Students will write a summary of their results and compare them to the classic "laws" of drainage=basin morphometry presented in their textbook.

## Description of the activity/assignment

The goal of this activity is for to students to observe and quantify the inherent organization within the channel network of a single drainage basin (a la Horton, 1945). The students will use the contour-crenulation method to flesh out the channel network within a selected drainage basin. They will then use the Strahler system to deterime the stream order of each channel segment. They then measure and average various attributes (slope, length, etc.) of the channel segments, by stream order. These data will then be plotted on semi-log graph paper to illustrate the matematical relationships between channel attributes and stream order. This activity gives students practice in delineating drainage divides and channel networks on topographic maps, using map scales to measure distances on topographic maps, and graphing data using a semi-log format. In addition, they are asked to compare their "real-world" results against the classic "laws" of basin morphometry presented in their textbook. This permits a discussion of sample size and measurement error versus theoretical relationships presented in a textbook.
Designed for a geomorphology course

## Determining whether students have met the goals

I check their results and graphs against the values that I previously obtained from analyzing the drainage basin. I also include a stream-ordering problem on the midterm exam.