Next week we will continue to address questions about the linkage between physical characteristics of streams and biological process, performance, or potential. Our discussion will focus on the classification systems used for naming channel units. I encourage you to visit a stream and attempt to "name" the units you see and sketch or photo-document your observations in your field books. If you care to examine an alternative paper the paper by Clifford (2006) "Physical habitat, eco-hydraulics and river design: a review
and re-evaluation of some popular concepts and methods" is available online.
I received a note from Justin Laughlin, Stream Restoration Biologist, today. He asks if students would want to assist with installation of cedar tree revetment on North Fork Roanoke near Blacksburg next Tuesday. If so give him a call and arrange a meeting time and place. Call 276 782 1627 (O), 276 780 0805 (Cell)
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Vadas, R. L., Jr., and D. J. Orth. 1998. Use of physical variable to discriminate visually determined mesohabitats types in North American Streams. Rivers 6(3): 143-159.
In “Use of physical variables to discriminate visually determined mesohabitats types in North America Streams,” Vadas and Orth (1998) used instream base-flow hydraulic measurements and substrate characteristics to support their visual habitat classification methodology. At several sites in the Roanoke River basin, they visually classified habitats into five types and compared depth, velocity, substrate, and complex hydraulic variables, such as Reynolds number and Froude number, measured in each type. They found that depth, velocity, and turbulence varied most consistently among habitat types, and that their original visual classification scheme effectively distinguished between extremes (shallow pools and fast riffles), but was less effective for distinguishing among habitats representing transitions between these extremes. They used these results to expand their original classification scheme to include seven habitat types which could be distinguished by objective criteria based on hydraulic variables.
In Halwas and Church’s paper “Channel units in small, high gradient streams on Vancouver Island, British Columbia,” the authors state that bed forms in small high gradient stream channels have not been addressed and they assert that slope can be a criterion for channel unit classification. The authors measured slope, width, flow regime and bed sediment substrates and categorized channel units into groups described by Grant et al (1990), using t-tests to assess differences between channel unit variables within groupings. The authors attest that slope is associated with some corresponding bed material and can be used alone to describe channel units, despite low precision in their measurements and the steepness of their streams compared to reaches in other studies, because of the relatively rare flows that form channel units and the non-alluvial nature of headwater stream bed substrates; once formed, channel units tend to be stable over prolonged periods of time. The main goal of the papers is to assess stream habitat classification units in steep un-impacted headwater streams and to determine which variables are most important for determining the class of individual stream units.
Halwas, K.L. and M. Church. 2002. Channel units in small, high gradient streams on Vancouver Island, British Columbia. Geomorphology 43: 242-256.
In “A hierarchical approach to classifying stream habitat features,” Hawkins et al. suggest that their a three-tier method of classifying stream habitats into fast and slow water features will help stream habitat managers easily apply biotic information from stream studies across the landscape to local riverscapes and can aid in scaling local studies to basin-level management. The authors classified stream channel units based on their flow speed and then further classified them based on gradient, percent super critical flow, bed roughness, mean velocity and step development into 18 classes. Overall, the authors feel they have created a useful and easily integrated stream unit classification, which they feel could use further validation from field data collection, especially in large rivers. The author’s goals are to develop a system that will allow easy and large-scale classification of habitats, which the authors see as critical for estimating population abundances across watersheds in long-term monitoring and conservation plans.
Hawkins, C.P., J.L Kershner, P.A. Bisson, M.D. Bryant, L.M. Decker, S.V. Gregory, D.A. McCullough, C.K. Overton, G.H. Reeves, R.J. Steedman, and M.K. Young. 1993. A hierarchical approach to classifying stream habitat features. Fisheries 18(6): 3-12.
Poole, G. C., C. A. Frissell, and S. C. Ralph. 1997. In-stream habitat unit classification: inadequacies of monitoring and some consequences for management. Journal of the American Water Resources Association 33(4): 879-896.
In “In-stream habitat unit classification: inadequacies of monitoring and some consequences for management,” Poole et al. critically evaluated the use habitat unit inventories as a tool to assess stream condition over time. They found four problems with habitat unit (or type) classification, which made application of this tool suspect: 1) repeatability was low because classification was inconsistent among observers, time, and sites; 2) precision was so low that differences were masked by noise or false conclusions were likely; 3) inventories lack sensitivity to changes in river condition, such as changes to geomorphology and processes, which they are meant to gauge; and 4) because stream classification is analyzed on a nominal scale, statistic approaches are limited. Despite these limitations which make use of this tool suspect for monitoring changes over time at a given site, Poole et al. admit this tool can be useful in studies that examine changes over long time periods, across larger geographical areas, and with large sample sizes that negate precision problems. For monitoring changes, they suggested moving away from habitat unit inventories toward using specific measures of channel structure and dynamics, and they suggest several alternative approaches for monitoring sites.
Chapter in Stream Ecology on Streamflow (Allan and Castillo 2007)
In the chapter entitled “Streamflow,” Allan and Castillo (2007) argued that we need to understand fundamental concepts about how water cycles through fluvial systems and also how those fluvial systems store and transport water if we are to address the increasing human pressures on these significant yet rare resources. Toward this end they surveyed three major components of fluvial systems (water cycle, instream flow, and flow variation); however, their survey was heavily dominated by two paradigms used to organize the complexity of fluvial systems: the water balance equation and the flow regime. Throughout this review they presented examples of how fluvial systems and their component parts vary across time and space (primarily a factor of climate) and also how human disturbance effects each. The purpose of this chapter was to provide an overview of what Allan and Castillo considered important concepts and paradigms in our understanding of fluvial systems.
Hawkins et al. (1993) provides an organizational framework to classify stream habitats. The authors use a hierarchical system containing three major levels that can be adjusted for the desired resolution. The first level is a distinction between slow water and fast water, the second level is based on the type of flow for fast water and the type of pool for slow water habitats, and the third level provides specific information about the characteristics of the specific habitat. The authors’ purpose is to establish an adaptable system that can efficiently describe habitat types, giving researchers and managers a common language and a useful tool for estimating stream habitat.
Hawkins, C.P., J.L Kershner, P.A. Bisson, M.D. Bryant, L.M. Decker, S.V. Gregory, D.A. McCullough, C.K. Overton, G.H. Reeves, R.J. Steedman, and M.K. Young. 1993. A hierarchical approach to classifying stream habitat features. Fisheries 18(6): 3-12.
Hawkins, et al. “A Hierarchical Approach to Classifying Stream Habitat Features.” (1993) states that current stream classification systems, such as the Bisson classification system, is insufficient and that a hierarchical system would resolve some of the problems with other classification systems. Hawkins et al presents three levels of a hierarchical system which can be amended given circumstance that one may encounter, while giving researchers and managers a common point to work from when assessing stream systems and classifying them. Hawkins et al attempts to bring streams together in a form of classification so that there is less guessing what it comes to analyzing the stream in order to develop a common starting place for stream classification. This article is meant for use by researcgers and managers that are seeking a better form of stream classification.
Vadas and Orth (1998) studied the Roanoke River watershed to develop a mesohabitat classification system. They collected microhabitat data at a total of six stations to classify macrohabitat into three categories and mesohabitat into seven categories. Macrohabitat could be describes as main channel, side channel, or backwater while mesohabitat could be characterized as deep, medium, and shallow pools, deep and medium runs, and fast and slow riffles. Hydraulic variables, such as depth and velocity and turbulence features, such as velocity:depth ratio and Reynolds numbers, were found to be the best determinants of these mesohabitats. Roughness variables, including substrate size and percent cover, were not found to be useful in classification because of increased variability in comparison to hydraulic and turbulence variables. The data analysis indicated that visual classifications of mesohabitats based on these parameters can be effective.
Vadas, R. L., Jr., and D. J. Orth. 1998. Use of physical variable to discriminate visually determined mesohabitats types in North American Streams. Rivers 6(3): 143-159.
Ian Jowett, “A Method for Objectively Identifying Pool, Run, and Riffle Habitats from Physical Measurements” (1993) argues the idea that identifying pools, runs, and riffles within a stream system is not as simple as many scientists assume. Jowett measures 1,112 points throughout a gravel-bed river to derive an objective method for distinguishing different stream or river habitats which are more in depth than simple measurements of water velocity and depth. Jowett felt as though these simple measurements did not suffice to fully explain certain habitats, and that from river system to river system, the measurements of the same type of habitat can vary greatly, therefore a new set of measurements including the Froude number and substrate composition were taken in order to better understand that river systems are different everywhere, but the habitats within the river systems can still offer the same information. This article is most likely to be used by fluvial morphologists, morphologists, or biologists who need to take samples from particular habitats, but may have had some confusion in the past about what defined a particular habitat.
In this journal article a method for objectively identifying pool, run, and riffle habitats from physica measurements, Jowett attempts to attempts to develop a set of classification rules for determining stream units by using physical characteristics like, substrate size, roughness, velocity/depth ratio, and Froude number to determine if any of these physical descriptors can adequately differentiate between pool, riffle, or run habitat. He takes measurements at 1112 points in three rivers and determines that the velocity/depth ratio and Froude number both differentiate between riffle and pool habitat. He notes that these measurements had difficulty differentiating run habitat from pool and riffle habitat. The purpose of this paper was to correlate physical conditions at a particular site to a subject assessment at that site and demonstrate the difficulty in visually determining a stream segment’s classification as river’s are not broken into distinct segments but are a continuum.
Jowett, I. G., A method for objectively identifying pool, run, and riffle habitats from physical
measurements. 1993. New Zealand Journal of Marine and Freshwater Research. 27: 241-248
In “A hierarchical approach to classifying stream habitat features” by Hawkins et al 1993, a functional system for defining specific stream habitats at different levels is introduced. The system focuses on improving past and often partially failed efforts on classifying habitats. Major emphasis is put on building stream habitat classification on a framework that is adaptable to varying conditions. For example, smaller order streams are going to have different feature parameters than larger rivers, so there must be a way to adjust from the framework to suit these. The authors use 3 levels of channel geomorphic units, increasing resolution as the system progresses. Level 1 breaks the channel geomorphic units into fast water (riffle) habitats and slow water (pool) habitats. Level 2 breaks fast water habitats into turbulent and non-turbulent categories, and slow water habitats into scour pool and dammed pool categories. First, level 3 divides turbulent habitats into fall, cascade, rapid, riffle, and chute. Next, non-turbulent is divided into sheet and run categories. Furthermore, scour pool is split into eddy, trench, mid-channel convergence, lateral, and plunge categories. Finally, dammed pool is split into debris, beaver, landslide, backwater, and abandoned channel categories. Level 3 habitats are further defined by their physical attributes. Hawkins et al realizes that their channel unit classification is just a framework, or a starting point for others to expand on, identifying potential problems and advantages of their system.
Hawkins, C.P., J.L. Kershner, P.A. Bisson, M.D. Bryant, L.M. Decker, S.V. Gregory, D.A. McCullough, C.K. Overton, G.H. Reeves, R.J. Steedman, and M.K. Young. 1993. A hierarchical approach to classifying stream habitat features. Fisheries 18(6): 3-12.
In their journal paper, ‘In-Stream Habitat Unit Classification: Inadequacies for Monitoring and some Consequences for Management’, Poole et al. (1997) , argue that habitat unit classification is often applied inappropriately with the intent of quantifying site-specific changes in aquatic habitat and stream morphology over time. They support this assertion by doing a review o f various authorities on the repeatability, transferability, precision and flexibility of habitat unit classification. In most cases, the application of this classification fell short of the standard required for adequate monitoring. The authors readily accept the fact that this method can have considerable utility for stratifying and organising inherently variable stream systems. The writers’ main purpose is to present a critical evaluation of the application of habitat-unit classification for quantifying aquatic habitat with the intention of monitoring a stream’s response to anthropogenic impact over time.
Poole, G. C, Christopher A. Frissell, and Stephen C. Ralph (1997). Journal of the American Water Resources Association. VOL. 33, NO.4. 879-869
In “In-stream habitat unit classification: inadequacies for monitoring and some consequences for management” by Poole et al, current issues with habitat unit classification are addressed. Four types of problems with classification were found: 1) observer inconsistency with subjectivity, 2) process changes don’t always translate into noticeable differences in habitats, 3) nominal data often restricts statistics, 4) long-term effects and solutions are often not considered. Finally, the authors discuss the place habitat unit classification has with monitoring, stating that it should not be used directly for monitoring, but instead to basically describe streams.
Poole, G.C., C.A. Frissell, and S.C. Ralph. 1997. In-stream habitat unit classification: inadequacies for monitoring and some consequences for management. Journal of the American Water Resources Association 33(4): 879-896.
Hawkins et al. (1993) in their journal paper, ‘A hierarchical Approach to
Classifying Stream Habitat Features’ , propose a hierarchical system of classifying stream habitats based on three increasing fine descriptions of the morphological and hydraulic properties of channel geomorphic units. They, first all, give some criteria of a good general classification system: 1) it should serve several purposes. 2) it should provide a standard frame of reference that facilitates communication among researchers and managers, and 3) habitat classes should be defined in an ecologically meaningful way that can be easily recognized by both researchers and managers. Following from this they lay out an elaborate representation of their proposed classification, which is broken down into three categories. The first level is the channel geomorphic unit (CGU). This is then broken down systematically in various sub-levels. The authors’ main purpose is to provide a consistent system of classification, which according to them, is non-existent.
Hawkins Charles P., Jeffrey L. Kershner, Peter A. Bisson, Mason D. Bryant, Lynn M.
Decker, Stanley V. Gregory, Dale A. McCullough, C. K. Overton, Gordon H. Reeves,
Robert J. Steedman and Michael K. Young (1993). A hierarchical Approach to Classifying Stream Habitat Features. Fisheries, vol. 18, No. 6. 3-12.
In the journal article “A hierarchical approach to classifying stream habitat features”, Hawkins et al. propose a hierarchical classification system based on three general stream categories that are then sub-divided into more detailed classifications. They state this classification system should meet three objectives: 1) habitat classes should be defined in an ecologically significant way that can be easily understood by researchers and managers, 2) the classes should be based on measureable variation at spatial scales meaningful to stream biota, and 3) the system should be flexible enough that researchers are able to use the system in multiple streams. The authors admit that the success of their proposed system will depend on the variance in physical characteristics within and between channel units and also that their system will require refinement and validation. The purpose of this paper is to attempt create a universal classification system and as a by-product, address some issues that users have had with Bisson’s (Bisson et al. 1982) classification scheme.
Hawkins Charles P., Jeffrey L. Kershner, Peter A. Bisson, Mason D. Bryant, Lynn M. Decker, Stanley V. Gregory, Dale A. McCullough, C. K. Overton, Gordon H. Reeves, Robert J. Steedman and Michael K. Young (1993). A hierarchical approach to classifying stream habitat features. Fisheries 18: 3- 12.
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