Table 2. Channel types and associated characteristics
|CP||cascade-pool||CPc-w||cobble||present, minor function|
|SP||step-pool||SPb-w||boulder||present, minimal function|
Figure 5. Nomogram used to determine channel morphology.
Figure 6. Channel morphologies of small- and intermediate-sized channels.
As an example of the use of Figure 5, use:
D = 10 cm d = 120 cm Wb = 20 m s = 1.5%
Following the lines in the nomogram produces a riffle-pool morphology with predominately gravel-textured materials (RPg). Large woody debris (LWD) is important in these channel types (see Figure 7).
Figure 7. Determining the influence of LWD on channel morphology.
If either the CP or SP morphologies are determined from Figure 5, it is necessary to determine if LWD is expected in the particular channel. The importance of LWD to channel functions depends on the width of the channel (also stream power, but this is considered implicitly in Figure 5). The functional role of LWD is given in Figure 7. For instance, if a channel is determined to be cascade-pool morphology, from Figure 7 it is apparent that when the channel is less than 30 m wide, LWD should be present. When the channel is wider than 30 m, LWD is present but not functioning. (Note that since LWD characteristics are to be used as field indicators of disturbance, it is necessary to know when LWD should, or should not, be present in channel.)
The nomogram is a tool to assist in determining the type of channel morphology. If, in the field, the nomogram indicates a type of morphology that appears incorrect, the field measures should be re-taken. For instance, if a step-pool morphology is determined from Figure 5, but the channel is clearly a riffle-pool morphology, the field values used (with emphasis on channel slope) should be checked.
Figure 8a. Small-sized channel morphology matrix showing levels of disturbance (degradation and aggradation).
Figure 8b. Intermediate-sized channel morphology matrix showing levels of disturbance (degradation and aggradation).
Disturbances associated with LWD are assessed by considering the functional role of debris in controlling the morphology (see Hogan et al., in press, for additional details concerning LWD functions). In certain channels, LWD controls the patterns of sediment erosion and deposition within the channel zone. The channel will adjust to any change if LWD is altered in its dimensions, orientation, or storage patterns. LWD plays an insignificant stream-forming role in other channel types (Figure 7).
Figure 9a. Field indicators of channel disturbance-sedimentological features.
Figure 9b. Field indicators of channel disturbance-bank features.
Figure 9c. Field indicators of channel disturbance-morphological features.
Figure 9d. Field indicators of channel disturbance-LWD features.
Several points should be noted concerning the channel keys. First, the keys are organized so that the undisturbed channel is located in the middle of each set of channel types. Three levels of aggraded channels are found in front of the undisturbed channel and three levels of degraded channels are located after the undisturbed channel. This series shows the progression of channel changes that occur if sediment and/or water quantity are increased (aggrading, for example, downstream of a landslide entry point to the channel) or decreased (degrading, for example, downstream of a barrier to sediment transport, such as a landslide-dammed channel). This series is given in Appendix 2. The three levels represent degrees of disturbance severity.
Second, the text associated with each channel disturbance level often indicates that a feature is becoming "more," "less," "coarser," "finer," etc. These terms refer to the progression of changes away from the undisturbed state (e.g., see title page of each channel type in Appendix 2). They indicate the sequence of changes that make up the disturbance.
Third, the keys provide generalized, typical examples of channel conditions along a reach. They are not intended to be exact duplicates of the conditions encountered (do not expect your field situation to be exactly the same as conditions shown in the keys). Finally, the "typical field indicators" listed in the keys do not have to be found in every case for that particular level of disturbance to be assigned. The indicators are included to show which indicators should, but not must, be present for the level of disturbance.
In the field, the morphology of each reach is determined according to the channel attributes measured in the field and with Figure 5. The level of disturbance is then assessed by inventorying the field indicators of channel disturbance and reviewing the deviation from the stable state, as shown in Appendix 2. All data are recorded on Field Form 1, and the proportion of each reach with disturbed morphology is calculated on Field Form 2. Finally, the information summarized on Field Form 2 is transferred to Form 8 of the Channel Assessment Procedure Guidebook.
Church, M. 1992. Channel morphology and typology. In The rivers handbook: Hydrological and ecological principles. Callow, C., and Petts, G. (eds.). Oxford: Basil Blackwell, p. 126-143.
Grant, G.E., F.J. Swanson, and M.G. Wolman. 1990. Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon. Geological Society of America Bulletin, 102: 340-352.
Hogan, D.L., S.A. Bird, and S. Rice. In press. Channel morphology and recovery processes. In Proceedings of the Carnation Creek and Queen Charlotte Islands Fish/Forestry Interaction Program: Applying 20 years of coastal research to management solutions. Chatwin, S., Hogan, D.L., and Tschaplinski, P. (eds.). B.C. Min. For. Victoria, B.C.
Kistritz, R.V. and G.L. Porter. 1993. Proposed wetland classification system for British Columbia. A discussion paper. B.C. Min. For., B.C. Min. Environ., Lands and Parks, and B.C. Conservation Data Centre. Victoria, B.C.
Leopold, L.B. 1994. A view of the river. Cambridge: Harvard University Press.