Study guide for week 7, Geog 427 1999

Geog 427/527: Fluvial Geomorphology
Winter 1999, University of Oregon

Study Guide for Week 7, Feb. 16-18

Tuesday, Feb. 16: Stream Classification

This topic integrates many concepts that we addressed earlier in the course. As you read this material, be sure to relate these concepts back to your reading and lectures on resistance, channel cross-sections, bedforms, channel pattern, etc.

In lecture, we will compare the Rosgen and Montgomery reach classification systems.

First reading for Tuesday 2/16: Knighton, p. 151-153

p. 151-153 in Knighton

Knighton points out that there has been a considerable history of river classification systems, dating at least from Davis’s (1899) youth-mature-old classification scheme.
There are many types of river classification schemes: stream order, biological classifications, hydrological classifications, and geomorphic classifications. We will focus on geomorphic classifications. River or channel classification systems allow one to classify a reach or segment (or in some cases, as small as a cross-section) of a river network as a specific type.
What geomorphic river classification approaches have we already discussed in this course?
What is the purpose of geomorphic river classification schemes, and how are they used?
Schumm (1963) classified channels on the basis of sediment composition of the bed and banks. Schumm’s classification and some of its implications are expressed in Fig. 5.16 on p. 206. Be sure to look at this figure.
In Table 5.1, Knighton proposes a modified classification based on bed and bank composition. What channel characteristics are generally thought to be related to (controlled by) bed and bank composition? (Hints: See p. 176, 188-189, 206, and perhaps others.)
Rosgen proposed a geomorphic channel classification system in the late 1980s. This classification system is widely used by the U.S. Forest Service, U.S. Bureau of Land Management, and other agencies, but there currently is a lot of debate about its value.
The Rosgen system is summarized in Fig. 5.1. Look at this figure closely. (The latest and most detailed presentation of this classification system is in his book: Rosgen, D., 1996. Applied River Morphology, which is on reserve for Geog 4/527 in the Science Library (GB 1203.2 .R677 1996). If you want more information on the Rosgen system, look at this book.)
In the Rosgen system quantitative measurements of five characteristics (shown in Fig. 5.1 – slope, sinuosity, width-depth ratio, entrenchment ratio, and bed and bank composition) are used to classify the reach to a specific type which is designated using a combination of letters and numbers (i.e., A4, F6, etc.). We will go over this figure, and the Rosgen system, in more detail in lecture. I will show some of Rosgen’s tables that relate channel type to channel behavior.

Second reading for Tuesday 2/16: Bisson and Montgomery, 1996, Valley segments, stream reaches, and channel units.

p. 23-25: Introduction	What are valley segments, stream reaches, and channel units? What is the purpose of a stream classification system, according to Bisson and Montgomery? What are the different types of stream classification systems? What are some qualities or hallmarks of a good stream classification system?
p. 26-28: Valley segment classification	What are the three valley segment types? What observable characteristics are used to classify valley segment type? What is the difference between transport-limited and supply-limited segments, and which types of segment belong to which group? What is a "zero-order" stream or segment? What is the difference between confined and unconfined segments? What are the differences between colluvial, alluvial and bedrock segments? For example, how are the dominant transport processes different in alluvial versus colluvial segments?
p. 28-32: Channel reach classification	Table 2.1 is important. What are the differences in gradient, bedform, pattern, sediment, and roughness elements among braided, regime, pool-riffle, plane-bed, step-pool and cascade reaches? [For roughness, be sure to relate the information in Table 2.1 to the table from the 1/14 lecture (in week 2 study guide).] How does and transport ability vary among these reach types? What is meant by the terms "laterally oscillatory" and "vertically oscillatory" bedform patterns? Which reach type(s) has the most pools?
p. 32-39: Channel unit classification	This section presents a classification of channel units (macro-scale bedforms) that is more detailed than simply riffle, pool, step, etc. Most importantly, a number of different types of pools are recognized. This classification system was developed in fisheries biology rather than geomorphology. Different unit types have different qualities for fish habitat. Although a detailed process-explanation for the formation of different unit types is not presented, Figure 2.3, Table 2.3 and the text show that different pool types occur in different positions within the channel and have different "forming constraints". Read through the text for each pool type, and become generally familiar with the pool terminology. Table 2.2 shows differences in hydraulic characteristics among the fast water units. You don’t need to memorize each unit type, but you should be able to understand and use Tables 2.2, and 2.3 .
p. 39-49: General design, Specific exercises	These sections discuss the general approach and methods for classifying reaches and units according to the system presented in this chapter. These sections are less important for our course than the preceding sections of this chapter, but read through these sections to get an idea of how this classification system is applied in the field. Which of the reach characteristics listed in Table 2.1 can be determined in the office (i.e. from maps and aerial photos) and which can only be determined in the field? Are channel units determined in the field or office?

Thursday, Feb. 18: Ecological Interactions in Channels

Reading: Gregory et al 1991, in the reading packet

We didn't get to this topic today. We passed back the midterm and discussed it. Then we finished channel classification systems and channel units.

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last update: 02/12/07 10:45 PM
Department of Geography, University of Oregon, Eugene OR, 97403-1251