The delivery and transport of sediment through mountain rivers affects aquatic habitat and water ... more The delivery and transport of sediment through mountain rivers affects aquatic habitat and water resource infrastructure. While climate change is widely expected to produce significant changes in hydrology and stream temperature, the effects of climate change on sediment yield have received less attention. In the northern Rocky Mountains, we expect climate change to increase sediment yield primarily through changes in temperature and hydrology that promote vegetation disturbances (i.e., wildfire, insect/pathogen outbreak, drought-related die off). Here, we synthesize existing data from central Idaho to explore (1) how sediment yields are likely to respond to climate change in semi-arid basins influenced by wildfire, (2) the potential consequences for aquatic habitat and water resource infrastructure, and (3) prospects for mitigating sediment yields in forest basins. Recent climate-driven increases in the severity and extent of wildfire suggest that basin-scale sediment yields within the next few years to decades could be greater than the long-term average rate of 146 T km − 2 year − 1 observed for central Idaho. These elevated sediment yields will likely impact downstream reservoirs, which were designed under conditions of historically lower sediment yield. Episodic erosional events (massive debris flows) that dominate post-fire sediment yields are impractical to mitigate, leaving road restoration as the most viable management opportunity for offsetting climate-related increases in sediment yield. However, short-term sediment yields from experimental basins with roads are three orders of magnitude smaller than those from individual fire-related events (on the order of 10 1 T km − 2 year − 1 compared to 10 4 T km − 2 year − 1 , respectively, for similar contributing areas), suggesting that road restoration would provide a relatively minor reduction in sediment loads at the basin-scale. Nevertheless, the ecologically damaging effects of fine sediment (material b 6 mm) chronically produced from roads will require continued management efforts.
Geomorphic and ecological effects of instream wood have been documented primarily along rivers in... more Geomorphic and ecological effects of instream wood have been documented primarily along rivers in the temperate zones. Instream wood loads in tropical rivers might be expected to differ from those in analogous temperate rivers because of the higher transport capacity and higher rates of wood decay in the tropics. We use data from four field sites in Costa Rica and Panama to demonstrate that wood loads are consistently lower in tropical rivers, despite substantial variations among tropical sites as a result of differences in mechanisms of wood recruitment. We develop a model of wood dynamics (recruitment, transport, and retention) based on differences in dominant wood recruitment mechanism. The steadystate end-member reflects sites where gradual recruitment of wood through individual tree fall creates a relatively consistent wood load through time and development of logjams is minimal. The episodic end-member reflects sites dominated by episodic mass recruitment via landslides or blowdowns. This facilitates formation of transient logjams, so that wood loads exhibit substantial spatial and temporal variation along the channel network. The model presented here should also apply to headwater streams in the temperate zone, although existing documentation suggests that jams are more persistent along streams in the temperate zone.
Land use practices in Colorado during the last two centuries altered the supply of sediment and w... more Land use practices in Colorado during the last two centuries altered the supply of sediment and water to many channels in the upper South Platte Basin. As a result of increased supply of sediment and mobility and reduced peak flows, the characteristics of pools associated with channel constrictions, referred to as forced pools, may have been altered. Increased supply of sediment and reduced transport capacity of high flows could lead to aggradation in forced pools. Channel confined by road corridors could lead to high velocities at normal flows, increased energy dissipation from riprap, or even increased pool frequency resulting from failed riprap. To assess potential alterations, four hypotheses were tested: (1) impacted streams will show significantly different mean volume of pools than a control stream; (2) mean volume of pools on streams where land-use activities increased the supply of sediment will be significantly different from streams solely affected by flow regulation; (3) the strongest change in characteristics of pools of impacted streams will be a reduced volume of pools; (4) streams affected by road corridors will show statistically lower spacing of pools than streams unaffected by roads. The downstream spacing and residual volume of twenty consecutive forced pools were surveyed on five streams in the Colorado Front Range that varied from no contemporary impact to multiple historical and contemporary impacts. ANCOVA with stepwise model selection indicated that degree of land-use (categorical), bankfull spacing of pools, upstream riffle slope and expansion ratio were all significant (α = 0.1) predictors of volume of pools (R 2 = 0.73). Simple linear regression of mean volume of pools and stream specific variables (gradient, drainage area and discharge) and least square means comparison of mean volume of pools indicated a need to standardize volumes of pools by slope and discharge so that the volumes of pools could be compared among different levels of land-use. Significant correlations between drainage area and volume of pools allowed volume of pools to be standardized by drainage area and thereby discharge. This dimensionless variable was also significantly correlated with channel slope, which permitted the construction of a new variable, PV QS (volume of pools standardized by discharge and slope). Least square means comparison of mean PV QS revealed that the control reach was significantly different from road-impacted reaches. Mean volume of pools was significantly larger in the control reach compared to all but one road-impacted stream. This was likely a function of higher wood loading in the control reach and the competence of high flows in the road-impacted reach. Streams affected by road corridors did not have significantly different bankfull spacing of pools from streams not impacted by roads. The multiple interactions among control and response variables explored in this study indicate the need to identify the most constrained and sensitive response variables when attempting to assess channel response to land use.
1] In this paper we examine the relationships among bedrock properties and hydraulics in shaping ... more 1] In this paper we examine the relationships among bedrock properties and hydraulics in shaping bedrock channel morphology at the reach scale. The Ocoee River and four other bedrock streams in the Blue Ridge province of the southeastern United States, which have reach-scale differences in bedrock erodibility controlled by lithologic and structural variation, are the focus of this study. We describe a simple conceptual model for concentrated erosion in bedrock channels and test three hypotheses in order to investigate the interactions among rock erodibility, characteristics of undulating rib-like bed forms, reach-scale gradient, and hydraulic roughness and energy dissipation. Substrate differences correlate with variation in reach morphology (i.e., gradient, bed form orientation, and amplitude), such that less erodible substrates are associated with steeper reach gradient and with transversely oriented ribs of greater amplitude. One-dimensional modeling in HEC-RAS indicated that in the reach with the least erodible substrate and greatest bed slope and rib amplitude, the reach-averaged hydraulic roughness was the greatest. Increased hydraulic roughness in steeper reaches points to the importance of positive and negative feedbacks in these systems: Greater substrate erosional resistance limits profile lowering, which likely creates steeper bed slopes and greater stream power, creating a self-enhancing feedback. This local increase in stream power is balanced by increased roughness resulting from the erosional processes that produce bedrock ribs, which represents a self-regulating feedback. The overall result reflects quantifiable adjustments between substrate resistance and hydraulic driving forces in bedrock channels.
Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in nort... more Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in north-eastern Costa Rica represent the first systematic data reported on wood loads in neotropical streams. For streams with drainage areas of 0·1-8·5 km 2 and gradients of 0·2-8%, wood load ranged from 3 to 34·7 m 3 wood/100 m channel and 41-612 m 3 wood/ha channel. These values are within the range reported for temperate streams. The variables wood diameter/flow depth, stream power, the presence of backflooding, and channel width/depth are consistently selected as significant predictors by statistical models for wood load. These variables explain half to two-thirds of the variability in wood load. These results, along with the spatial distribution of wood with respect to the thalweg, suggest that transport processes exert a greater influence on wood loads than recruitment processes. Wood appears to be more geomorphically effective in altering bed elevations in gravel-bed reaches than in reaches with coarser or finer substrate. Figure 2. Views of (A) site 11, El Surá, with slope of 5·91%, and drainage area of 3·26 km 2 ; (B) site 17, Quebrada Esquina, with slope of 3·17%, and drainage area of 1·64 km 2 ; (C) site 3, El Surá, with slope of 0·24%, and drainage area of 4·76 km 2 ; (D) site 1, Taconazo, with a slope of 0·32%, and drainage area of 0·28 km 2 .
1] An 11-year monitoring study begun in 1996 evaluates wood mobility in five Colorado Rocky Mount... more 1] An 11-year monitoring study begun in 1996 evaluates wood mobility in five Colorado Rocky Mountain streams. Each channel reach is 40-70 m in length. Initial surveys included channel dimensions and arrangement of each piece of wood. Annual resurveys focused on wood arrangement and persistence. Average diameter of 15 cm and length of 3.2 m varied little among sites. Average yearly mobility ranged from 16% to 23%. Average residence time was 3.4 years. Wood load correlates positively with valley width and channel gradient, and negatively with relative substrate submergence and mean annual peak discharge. Survival analysis revealed that individual piece residence time was controlled by a nondimensional piece length and peak unit stream power during the year of removal. Residence time increases as piece length relative to channel width decreases, which could be explained by a greater integration of the flow field for longer pieces. Mobility of individual pieces of wood is controlled primarily by piece characteristics (length, diameter, type). Likelihood of mobility is smallest for buried pieces. The brevity of residence time relative to studies from other regions likely results from relatively low wood loads in these channels after timber harvesting cleared both instream and riparian wood supply more than a century ago. Although individual pieces of wood are exchanged, wood load and the location of individual logjams remain relatively constant.
The delivery and transport of sediment through mountain rivers affects aquatic habitat and water ... more The delivery and transport of sediment through mountain rivers affects aquatic habitat and water resource infrastructure. While climate change is widely expected to produce significant changes in hydrology and stream temperature, the effects of climate change on sediment yield have received less attention. In the northern Rocky Mountains, we expect climate change to increase sediment yield primarily through changes in temperature and hydrology that promote vegetation disturbances (i.e., wildfire, insect/pathogen outbreak, drought-related die off). Here, we synthesize existing data from central Idaho to explore (1) how sediment yields are likely to respond to climate change in semi-arid basins influenced by wildfire, (2) the potential consequences for aquatic habitat and water resource infrastructure, and (3) prospects for mitigating sediment yields in forest basins. Recent climate-driven increases in the severity and extent of wildfire suggest that basin-scale sediment yields within the next few years to decades could be greater than the long-term average rate of 146 T km − 2 year − 1 observed for central Idaho. These elevated sediment yields will likely impact downstream reservoirs, which were designed under conditions of historically lower sediment yield. Episodic erosional events (massive debris flows) that dominate post-fire sediment yields are impractical to mitigate, leaving road restoration as the most viable management opportunity for offsetting climate-related increases in sediment yield. However, short-term sediment yields from experimental basins with roads are three orders of magnitude smaller than those from individual fire-related events (on the order of 10 1 T km − 2 year − 1 compared to 10 4 T km − 2 year − 1 , respectively, for similar contributing areas), suggesting that road restoration would provide a relatively minor reduction in sediment loads at the basin-scale. Nevertheless, the ecologically damaging effects of fine sediment (material b 6 mm) chronically produced from roads will require continued management efforts.
Geomorphic and ecological effects of instream wood have been documented primarily along rivers in... more Geomorphic and ecological effects of instream wood have been documented primarily along rivers in the temperate zones. Instream wood loads in tropical rivers might be expected to differ from those in analogous temperate rivers because of the higher transport capacity and higher rates of wood decay in the tropics. We use data from four field sites in Costa Rica and Panama to demonstrate that wood loads are consistently lower in tropical rivers, despite substantial variations among tropical sites as a result of differences in mechanisms of wood recruitment. We develop a model of wood dynamics (recruitment, transport, and retention) based on differences in dominant wood recruitment mechanism. The steadystate end-member reflects sites where gradual recruitment of wood through individual tree fall creates a relatively consistent wood load through time and development of logjams is minimal. The episodic end-member reflects sites dominated by episodic mass recruitment via landslides or blowdowns. This facilitates formation of transient logjams, so that wood loads exhibit substantial spatial and temporal variation along the channel network. The model presented here should also apply to headwater streams in the temperate zone, although existing documentation suggests that jams are more persistent along streams in the temperate zone.
Land use practices in Colorado during the last two centuries altered the supply of sediment and w... more Land use practices in Colorado during the last two centuries altered the supply of sediment and water to many channels in the upper South Platte Basin. As a result of increased supply of sediment and mobility and reduced peak flows, the characteristics of pools associated with channel constrictions, referred to as forced pools, may have been altered. Increased supply of sediment and reduced transport capacity of high flows could lead to aggradation in forced pools. Channel confined by road corridors could lead to high velocities at normal flows, increased energy dissipation from riprap, or even increased pool frequency resulting from failed riprap. To assess potential alterations, four hypotheses were tested: (1) impacted streams will show significantly different mean volume of pools than a control stream; (2) mean volume of pools on streams where land-use activities increased the supply of sediment will be significantly different from streams solely affected by flow regulation; (3) the strongest change in characteristics of pools of impacted streams will be a reduced volume of pools; (4) streams affected by road corridors will show statistically lower spacing of pools than streams unaffected by roads. The downstream spacing and residual volume of twenty consecutive forced pools were surveyed on five streams in the Colorado Front Range that varied from no contemporary impact to multiple historical and contemporary impacts. ANCOVA with stepwise model selection indicated that degree of land-use (categorical), bankfull spacing of pools, upstream riffle slope and expansion ratio were all significant (α = 0.1) predictors of volume of pools (R 2 = 0.73). Simple linear regression of mean volume of pools and stream specific variables (gradient, drainage area and discharge) and least square means comparison of mean volume of pools indicated a need to standardize volumes of pools by slope and discharge so that the volumes of pools could be compared among different levels of land-use. Significant correlations between drainage area and volume of pools allowed volume of pools to be standardized by drainage area and thereby discharge. This dimensionless variable was also significantly correlated with channel slope, which permitted the construction of a new variable, PV QS (volume of pools standardized by discharge and slope). Least square means comparison of mean PV QS revealed that the control reach was significantly different from road-impacted reaches. Mean volume of pools was significantly larger in the control reach compared to all but one road-impacted stream. This was likely a function of higher wood loading in the control reach and the competence of high flows in the road-impacted reach. Streams affected by road corridors did not have significantly different bankfull spacing of pools from streams not impacted by roads. The multiple interactions among control and response variables explored in this study indicate the need to identify the most constrained and sensitive response variables when attempting to assess channel response to land use.
1] In this paper we examine the relationships among bedrock properties and hydraulics in shaping ... more 1] In this paper we examine the relationships among bedrock properties and hydraulics in shaping bedrock channel morphology at the reach scale. The Ocoee River and four other bedrock streams in the Blue Ridge province of the southeastern United States, which have reach-scale differences in bedrock erodibility controlled by lithologic and structural variation, are the focus of this study. We describe a simple conceptual model for concentrated erosion in bedrock channels and test three hypotheses in order to investigate the interactions among rock erodibility, characteristics of undulating rib-like bed forms, reach-scale gradient, and hydraulic roughness and energy dissipation. Substrate differences correlate with variation in reach morphology (i.e., gradient, bed form orientation, and amplitude), such that less erodible substrates are associated with steeper reach gradient and with transversely oriented ribs of greater amplitude. One-dimensional modeling in HEC-RAS indicated that in the reach with the least erodible substrate and greatest bed slope and rib amplitude, the reach-averaged hydraulic roughness was the greatest. Increased hydraulic roughness in steeper reaches points to the importance of positive and negative feedbacks in these systems: Greater substrate erosional resistance limits profile lowering, which likely creates steeper bed slopes and greater stream power, creating a self-enhancing feedback. This local increase in stream power is balanced by increased roughness resulting from the erosional processes that produce bedrock ribs, which represents a self-regulating feedback. The overall result reflects quantifiable adjustments between substrate resistance and hydraulic driving forces in bedrock channels.
Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in nort... more Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in north-eastern Costa Rica represent the first systematic data reported on wood loads in neotropical streams. For streams with drainage areas of 0·1-8·5 km 2 and gradients of 0·2-8%, wood load ranged from 3 to 34·7 m 3 wood/100 m channel and 41-612 m 3 wood/ha channel. These values are within the range reported for temperate streams. The variables wood diameter/flow depth, stream power, the presence of backflooding, and channel width/depth are consistently selected as significant predictors by statistical models for wood load. These variables explain half to two-thirds of the variability in wood load. These results, along with the spatial distribution of wood with respect to the thalweg, suggest that transport processes exert a greater influence on wood loads than recruitment processes. Wood appears to be more geomorphically effective in altering bed elevations in gravel-bed reaches than in reaches with coarser or finer substrate. Figure 2. Views of (A) site 11, El Surá, with slope of 5·91%, and drainage area of 3·26 km 2 ; (B) site 17, Quebrada Esquina, with slope of 3·17%, and drainage area of 1·64 km 2 ; (C) site 3, El Surá, with slope of 0·24%, and drainage area of 4·76 km 2 ; (D) site 1, Taconazo, with a slope of 0·32%, and drainage area of 0·28 km 2 .
1] An 11-year monitoring study begun in 1996 evaluates wood mobility in five Colorado Rocky Mount... more 1] An 11-year monitoring study begun in 1996 evaluates wood mobility in five Colorado Rocky Mountain streams. Each channel reach is 40-70 m in length. Initial surveys included channel dimensions and arrangement of each piece of wood. Annual resurveys focused on wood arrangement and persistence. Average diameter of 15 cm and length of 3.2 m varied little among sites. Average yearly mobility ranged from 16% to 23%. Average residence time was 3.4 years. Wood load correlates positively with valley width and channel gradient, and negatively with relative substrate submergence and mean annual peak discharge. Survival analysis revealed that individual piece residence time was controlled by a nondimensional piece length and peak unit stream power during the year of removal. Residence time increases as piece length relative to channel width decreases, which could be explained by a greater integration of the flow field for longer pieces. Mobility of individual pieces of wood is controlled primarily by piece characteristics (length, diameter, type). Likelihood of mobility is smallest for buried pieces. The brevity of residence time relative to studies from other regions likely results from relatively low wood loads in these channels after timber harvesting cleared both instream and riparian wood supply more than a century ago. Although individual pieces of wood are exchanged, wood load and the location of individual logjams remain relatively constant.
Uploads
Papers by Jaime Goode