Geog 427/527: Fluvial Geomorphology
Winter 1999, University of Oregon
Study Guide for Week 3, Jan. 19-21
Exercise 2 is now on the exercises web page, and a copy is also in the Geog 4/527 notebook that is on reserve in the Map Library. The photos and cross section diagrams needed for Part A are in the Map Library notebook; I hope to get these posted on the web in a day or two.
Tuesday, Jan. 19: Thresholds of erosion, bank erosion (con.)
Last Thursday we finished up equations of flow, and started on thresholds of erosion (bed sediment entrainment). On Thursday I finished through boundary shear stress and critical shear stress. Today we covered with dimensionless shear stress and then cover other, empirical methods for predicting entrainment. The study questions for this material are in the study guide for week 2.
The table I used near the end of last Thursday’s lecture, for types of resistance in different channel types, is now on the study guide for week 2.
| p. 113-118: Bank erosion: |
What is the difference in sediment characteristics between channel beds
and channel banks? What is the difference between hydraulic action and mass failure? What processes are involved in hydraulic action that lead to bank retreat? What are the processes involved in mass failure of banks? What conditions lead to mass failure? How do different sediment materials behave differently in bank retreat? What are the negative environmental effects of bank retreat? |
Copies of some of the transparencies I used in this lecture are in the notebook in the Map Library.
Thursday, Jan. 21: Sediment transport
| p. 118-120: Introduction to sediment transport | Know the differences between dissolved load, wash load and bed-material
load (hint: types of material). Know the differences between bed transport and suspended transport (hint: type of movement). Fig. 4.6 is an important figure that shows different types of sediment movement, and shows the relationship between sediment inputs, storage, and sediment outputs. |
| p. 120-121: Dissolved load | Does dissolved load increase or decrease with increasing discharge? What
is the difference between total dissolved load and dissolved load concentration? What are the units of measurement for total dissolved load, and for dissolved load concentration? Note: the same units are also used for total suspended load, and for suspended load concentration. |
| p. 121-126: Wash load | How do suspended sediment concentration and bedload concentration vary
from the water surface to the channel bed? Empirical relationships between suspended sediment concentration and water discharge (also called suspended sediment rating curves) are important; you should know the general form of these relationships. Fig. 4.8C shows a data set from which a suspended sediment rating curve can be constructed. Why does suspended sediment concentration, for a given water discharge level, vary from season to season? Why does suspended sediment concentration, for a given water discharge level, vary from rising limb to falling limb of a peak flow hydrograph? What are some of the environmental problems related to increases in suspended sediment discharge? To decreases in suspended sediment discharge? |
| p. 126-129: Bedload transport and compexity of modes of transport | Fig. 4.9B illustrates the difference between contact transport (rolling,
sliding), saltation, and suspension. Is there an abrupt on/off threshold for bedload transport? If not, you should be able to describe a) how modes of transport may vary for a specific grain (Fig. 4.9C and related text); and b) how the number of grains in transport and size of grains in transport varies between phase I and phase II transport (Fig. 4.9D, text on p. 128-9). When bedload is in transport, does the bedload grain move as fast as the water? What is meant by the statement "bedload transport is characteristically intermittent" (p. 129)? What factors are mentioned as influencing the grain size of bedload in transport, the amount of bedload in transport, and the path length of an individual grain? What is an armour layer (armor layer in the US of A)? (Also see p. 131.) How does it influence bedload transport? How does it behave differently in phase I versus phase II transport? |
| p. 130-36: Sediment transport rates | What term or characteristic is predicted by bedload transport equations
(i.e., what is qsb)? How are the Duboys, Schoklitsch and Bagnold bedload transport equations different? How is the Einstein equation different from these three? Are these equations good at predicting bedload transport? What are some examples of (or evidence for) spatial variability of bedload transport? What are some mechanisms that explain shorter-term pulses of bedload transport? What are some mechanisms that explain longer-term pulses? During a high-flow event, how does the rate of bedload transport vary in relation to the discharge hydrograph? Does bedload constitute most of the sediment load of a typical river? How is bedload transport distributed across the flows of different magnitudes that a site (a cross section) experiences? Andrews and Nankervis assessed the magnitude-frequency relationship of bed-material transport in western U.S. rivers – how often does flow that is effective in carrying most of the bedload occur? |
| p. 136-41: Downstream changes in bed material characteristics | How does bed material size vary going downstream in a typical river? What processes are thought to be responsible for the systematic change in bed material size going downstream? What factors can make a river behave differently from the typical river, in terms of downstream pattern of bed material size? How does sorting and shape of bed material change going downstream? |
last update: 02/12/07 10:45 PM
Department of Geography, University of Oregon, Eugene OR, 97403-1251