This study examines sediment storage and transfers in gullies of coastal British Columbia, and how logging affects sediment storage and transfers. Both fluvial and debris flow transport of sediment occur in gullies, and the amount of fluvial transport of sediment which occurs will affect the magnitude of a subsequent debris flow. Coarse woody debris (CWD) may affect the storage and transfer of sediment in the gully channel, and logging can affect the supply and type of CWD. To determine whether logging affects storage and transfer of sediment in gullies, sediment budgets were constructed for gullies in four treatment classes: A. Logged, slash full, no recent debris flows : "slash-full (SF)." B. Logged, slash removed, no recent debris flows : "slash-clear (SC)." C. Logged, naturally scoured by debris flows : "torrented (T)." D. Unlogged, naturally loaded with CWD : "unlogged (U)." Each sediment budget had input to the channel, storage in the channel, and output from the channel estimated. Significant differences between treatment types occurred, summarized below. Treatment classes grouped together (in brackets) did not have significant differences. Budget term : Input, greatest→least, Torrented→Slash-full→(Unlogged and Slash-clear). Budget term : Storage, greatest→least, Torrented→Unlogged→Slash-clear. Budget term : Output, greatest→least, Slash-clear→(Torrented and Unlogged)→Slash-full. One objective of the study was to assess the effectiveness and feasibility of cleaning slash from the gully channels. To be effective, cleaning slash must either reduce the magnitude of a debris flow in a treated gully, or else reduce the likelihood of initiation of a debris flow in the treated gully. Removal of slash will reduce the volume of a subsequent debris flow by about 15 percent, simply from the reduction in the amount of CWD. Reduction in sediment stored in the treated channel may reduce the volume of a debris flow by a further 4 percent. There is no evidence that removing slash will decrease the likelihood of initiation of a debris flow.

Headwater streams typically have no fish, owing to steep gradients and impassible barriers; therefore, scientific research and protection measures have been focused on fish bearing streams. The Scientific Panel for Sustainable Forest Practices in Clayoquot Sound (CSP) developed a channel classification system which is pertinent to all streams, fishless and fish bearing alike, and upon which management prescriptions in Clayoquot Sound, Vancouver Island, British Columbia are based (CSP, 1995). The CSP classification delineates channels according to four physical criteria: bed material, gradient, entrenchment, and width. The current study was undertaken to determine the efficacy with which the CSP classification system delineates small, steep streams, on the basis of channel geomorphic units within them, and to examine the benthic macroinvertebrate habitat capability of these geomorphic units. Falls, bedrock cascades, boulder cascades, rapids, chutes, riffles, glides, and pools were described according to their bed slope and dominant channel-material type and organization. In addition, the area of each geomorphic unit was measured. Seventeen streams were grouped into four CSP channel classes which were compared with respect to the mean relative proportion of class area in geomorphic units. Stratified random benthic samples were extracted from geomorphic units in order to investigate and to compare their habitat capability. "Alluvial channels" in the study exhibited only weak, very infrequent fluvial transport; therefore, they were termed semi-alluvial. In general, high gradient geomorphic units (i.e. bedrock and boulder cascades) were dominant in steep, largely non-alluvial channels. Lower gradient units (i.e. riffles and rapids) were common in semi-alluvial streams with more mild slopes. Accordingly, channel classes with opposing bed material and gradient designations exhibited notable differences with respect to relative proportions of geomorphic units while width and entrenchment designations exerted little influence on channel organization. Ultimately, only two of the four CSP classification criteria effectively systematized channels on the basis of channel geomorphic units within them. Abundance of benthic macroinvertebrates was greatest in riffles (≈100 individuals per two minute kick sample), followed by rapids (≈80 individuals/sample), pools (≈70 individuals/sample), boulder cascades (≈60 individuals/sample), chutes (≈50 individuals/sample), and lowest in bedrock cascades (≈25 individuals/sample). In addition, abundance of invertebrates in channels with ephemeral flow regimes was considerably lower compared to channels with seasonal or perennial flow regimes. Ordination of macroinvertebrate taxa showed that community structure of bedrock cascades and chutes were similar but different from other habitats. Similarly, the benthic macroinvertebrate community structure of channels with ephemeral flow regimes was very distinct.

This study examines sediment storage and transfers in gullies of coastal British Columbia, and how logging affects sediment storage and transfers. Both fluvial and debris flow transport of sediment occur in gullies, and the amount of fluvial transport of sediment which occurs will affect the magnitude of a subsequent debris flow. Coarse woody debris (CWD) may affect the storage and transfer of sediment in the gully channel, and logging can affect the supply and type of CWD. To determine whether logging affects storage and transfer of sediment in gullies, sediment budgets were constructed for gullies in four treatment classes: A. Logged, slash full, no recent debris flows : "slash-full (SF)." B. Logged, slash removed, no recent debris flows : "slash-clear (SC)." C. Logged, naturally scoured by debris flows : "torrented (T)." D. Unlogged, naturally loaded with CWD : "unlogged (U)." Each sediment budget had input to the channel, storage in the channel, and output from the channel estimated. Significant differences between treatment types occurred, summarized below. Treatment classes grouped together (in brackets) did not have significant differences. Budget term : Input, greatest→least, Torrented→Slash-full→(Unlogged and Slash-clear). Budget term : Storage, greatest→least, Torrented→Unlogged→Slash-clear. Budget term : Output, greatest→least, Slash-clear→(Torrented and Unlogged)→Slash-full. One objective of the study was to assess the effectiveness and feasibility of cleaning slash from the gully channels. To be effective, cleaning slash must either reduce the magnitude of a debris flow in a treated gully, or else reduce the likelihood of initiation of a debris flow in the treated gully. Removal of slash will reduce the volume of a subsequent debris flow by about 15 percent, simply from the reduction in the amount of CWD. Reduction in sediment stored in the treated channel may reduce the volume of a debris flow by a further 4 percent. There is no evidence that removing slash will decrease the likelihood of initiation of a debris flow. / Arts, Faculty of / Geography, Department of / Graduate

Headwater streams typically have no fish, owing to steep gradients and impassible barriers; therefore, scientific research and protection measures have been focused on fish bearing streams. The Scientific Panel for Sustainable Forest Practices in Clayoquot Sound (CSP) developed a channel classification system which is pertinent to all streams, fishless and fish bearing alike, and upon which management prescriptions in Clayoquot Sound, Vancouver Island, British Columbia are based (CSP, 1995). The CSP classification delineates channels according to four physical criteria: bed material, gradient, entrenchment, and width. The current study was undertaken to determine the efficacy with which the CSP classification system delineates small, steep streams, on the basis of channel geomorphic units within them, and to examine the benthic macroinvertebrate habitat capability of these geomorphic units. Falls, bedrock cascades, boulder cascades, rapids, chutes, riffles, glides, and pools were described according to their bed slope and dominant channel-material type and organization. In addition, the area of each geomorphic unit was measured. Seventeen streams were grouped into four CSP channel classes which were compared with respect to the mean relative proportion of class area in geomorphic units. Stratified random benthic samples were extracted from geomorphic units in order to investigate and to compare their habitat capability. "Alluvial channels" in the study exhibited only weak, very infrequent fluvial transport; therefore, they were termed semi-alluvial. In general, high gradient geomorphic units (i.e. bedrock and boulder cascades) were dominant in steep, largely non-alluvial channels. Lower gradient units (i.e. riffles and rapids) were common in semi-alluvial streams with more mild slopes. Accordingly, channel classes with opposing bed material and gradient designations exhibited notable differences with respect to relative proportions of geomorphic units while width and entrenchment designations exerted little influence on channel organization. Ultimately, only two of the four CSP classification criteria effectively systematized channels on the basis of channel geomorphic units within them. Abundance of benthic macroinvertebrates was greatest in riffles (≈100 individuals per two minute kick sample), followed by rapids (≈80 individuals/sample), pools (≈70 individuals/sample), boulder cascades (≈60 individuals/sample), chutes (≈50 individuals/sample), and lowest in bedrock cascades (≈25 individuals/sample). In addition, abundance of invertebrates in channels with ephemeral flow regimes was considerably lower compared to channels with seasonal or perennial flow regimes. Ordination of macroinvertebrate taxa showed that community structure of bedrock cascades and chutes were similar but different from other habitats. Similarly, the benthic macroinvertebrate community structure of channels with ephemeral flow regimes was very distinct. / Arts, Faculty of / Geography, Department of / Graduate