JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION VOL. 38, NO.1 AMERICANWATER RESOURCES ASSOCIATION FEBRUARY 2002

DIAGNOSTIC APPROACH TO ASSESSMENT AND MONITORINGl

David R. Montgomery and Lee H. MacDonald2

ABSTRACT: We suggest that a diagnostic procedure, not unlike INTRODUCTION that followed in medical practice, provides a logical basis for stream channel assessment and monitoring. Our argument is based on the observation that a particular indicator or measurement of stream Effective enforcement of legal mandates to protect channel condition can mean different things depending upon the water quality and aquatic habitat presumesan ability local geomorphic context and history of the channel in question. to reliably evaluate the effect of past, present, and This paper offers a conceptual framework for diagnosing channel reasonably foreseeableland use decisions on stream condition, evaluating channel response, and developing channel monitoring programs. The proposed diagnostic framework assesses channel conditions and functions (MacDonald et al., reach-level channel conditions as a function of location in the chan- 1991).Accurate channel assessmentsare particularly nel network, regional and local biogeomorphic context, controlling important when the presenceof threatened or endan- influences such as supply and transport capacity, riparian gered species necessitates a careful evaluation of vegetation, the supply of in-channel flow obstructions, and distur- existing and potential land use impacts on watershed bance history. Field assessments of key bottom and active channel characteristics are needed to formulate an accurate diagno- processesand conditions. Effective methods to assess sis of channel conditions. A similar approach and level of under- and monitor channel condition are neededto evaluate standing is needed to design effective monitoring programs, as the successof efforts to mitigate impacts and stream type and channel state greatly affect the type and magni- restore degraded channels (NRC, 1992). At present, tude of channel response to changes in and sediment channel assessmentand monitoring techniques vary loads. General predictions are made for five channel types with respect to the response of various stream characteristics to an widely in their validity, relative sensitivity, and foun- increase in coarse sediment inputs, fme sediment inputs, and the dation in fluvial geomorphology.Moreover, the com- size and frequency of peak flows, respectively. These predictions plexity of channel condition and responsehas limited provide general hypotheses and guidance for channel assessment the development of explicit protocols to assess and and monitoring. However, the formulation of specific diagnostic cri- monitor stream channel condition (Bauer and Ralph, teria and monitoring protocols must be tailored to specific geo- graphic areas because of the variability in the controls on channel 1999). condition within basins and between regions. The diagnostic Three basic precepts underlie our conceptual approach to channel assessment and monitoring requires a rela- framework for channel assessment and monitoring. tively high level of training and experience, but proper application First, stream channel condition reflects the capability should result in useful interpretation of channel conditions and of the channel.to accommodateor resist changedue to response potential. (KEY TERMS: channel assessment; monitoring; applied fluvial geo- inputs of sediment, water, organic matter, or alter- morphology; watershed management; wildland hydrology.) ations of the riparian vegetation. Second, different channel types vary in their sensitivity and response to changes in inputs or local controls. Third, catch- ment- and local-scaledifferences in channel processes, historical disturbance, topography, lithology, struc- tural controls, and geomorphic history result in a

lpaper No.00128 of the Journal of the American Water ResourcesAssociation. Discussions are open until October 1,2002. 2Respectively, Professor, Department of Geological Sciences, University of Washington, Seattle, Washington 98195-1310; and Professor, Department of Earth Resources, Colorado State University, Fort Collins, Colorado 80523-1482 (E-Mail/Montgomery: [email protected] ton.edu).

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1 JAWRA Montgomery and MacDonald variety of channel types throughout a watershed example, a pulse input of fine sediment into a steep (Schumm, 1963; Paustian et at., 1992; Whiting and channel may be rapidly transported downstream, but Bradley, 1993; Montgomery and Buffington, 1997; persist in a lower-gradient reach where it could have 1998).The application of these principles leads to the a relatively large effect on aquatic ecosystems(Coats conclusion that channel assessment and monitoring et at., 1985; Ziemer et at., 1991; Madej and Ozaki, proceduresmust consider: (1) differences in sensitivi- 1996). The multiple controls on stream channels and ty and responsedue to channel type; (2) spatial and the variety of potential channel responsesmean that temporal variability in the input parameters in differ- effective procedures to assessstream channel condi- ent portions of a watershed; and (3) the effects of tion must explicitly considerthe spatial location with- other controls at both reach and watershed scales. in the channel network, channel type, temporal Although recent studies have explicitly recognized variability in inputs, historic condition, and the per- different stream types, many channel assessmentand sistenceof different inputs over spaceand time. monitoring programs do not adjust their procedures In other applied sciences,such as medicine, a diag- or stratify sampling by stream type (e.g., Pfankuch, nostic procedurehas been recognizedas the appropri- 1975; Sanderset at., 1987; Hankin and Reeves,1988; ate framework for evaluating the state of complex Ward et at., 1990; MacDonald et at., 1991). In addi- systems. We contend that a comparable diagnostic tion, many channel assessment procedures rely on processcan provide a useful framework for interpret- simple indicators of channel condition, scorecards ing and assessingchannel condition. Hence the first that impose standardized expectationsof channel con- objective of this paper is to define a diagnostic proce- ditions, or a comparison of characteristics to pre- dure to guide the assessment and monitoring of selected "reference" reaches (e.g., Pfankuch, 1975; stream channel condition. The second objective is to Bevengerand King, 1995).These approachesgeneral- show how the same logic is needed to identify those ly do not fully recognize the extent to which the monitoring locations and channel characteristics that results can be affected by the inherent differencesin are most likely to respond to management impacts. biogeomorphic context and different types of chan- We present a series of tables that predict the general nels. In the absence of a better understanding of effects of increases in peak flows, fine sediment, and expected condition and likely cause-and-effect rela- coarsesediment on specific channel characteristics as tions, management decisions may be misguided and a function of stream type. The final section of the potentially counter-productive. paper addressesthe advantagesand disadvantagesof Nonetheless,the desire to easily assessand moni- using a diagnostic approach. We acknowledge an tor channel conditions means that there is a continu- implicit bias towards mountain in the west- ing search for a sensitive, quick, and universal ern U.S. becauseour experienceis largely from this procedure to evaluate the condition of stream chan- region and this is where much of the relevant nels and monitor their response to land use. This research has been conducted.Nevertheless, basic geo- searchand many current monitoring projects implicit- morphic principles and our own field observations ly assumethat a single characteristic or channel rat- lead us to believe that these ideas are more widely ing will be applicable over a wide geographic area, applicable. and have minimal spatial and temporal variability. But a particular measurement or channel rating can have very different implications depending on the stream type and location in the channel network. DIAGNOSTIC PROCESS Eroding banks might be the norm for channels in arid or semi-arid areas, but an indicator of severe distur- Diagnosis is defined as "a careful examination and bance for streams in otherwise well-vegetated moun- analysis of the facts in an attempt to understand or tain meadows.Bed material particle size can vary as explain something." A diagnostic framework for much within a cross section as from the headwaters assessingchannel condition should formalize the pro- to the river mouth. The tremendous spatial variabili- cedure and logic that is used by well-trained, objec- ty in stream channel characteristics is further compli- tive, and observant professionals. By definition, the cated by the temporal variability resulting from the diagnosis of a complex system requires one to assess sporadic and often unpredictable variations in dis- current condition relative to some potential state, charge, sediment inputs, riparian vegetation, and evaluate the effects of both known and inferred past other controls on channel condition. influences, and determine the relative importance of The assessment of channel condition is further factors controlling the current state of a stream or complicatedby the fact that the effect of a natural or river. Thus a diagnostic approach should incorporate anthropogenic disturbance may persist for different at least the following three phases:(1) define the sys- periods in different portions of a channel network. For tem of interest and the controlling variables; (2) use

JAWRA 2 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION Diagnostic Approach to Stream Channel Assessment and Monitoring qualitative and quantitative observations to charac- stream channels and aquatic habitat condition rather terize the current state of the system; and (3) evalu- than the more general conceptof stream health. ate the controlling variables and current symptomsto infer both relative condition and the causal mecha- nisms producing this condition. Management pre- Past, present and future inputs of scriptions can then be developed, and monitoring conductedto both confirm or revise the diagnosis and Sediment Water Wood assesschanges at the reach or watershed scale. There are obvious parallels between a channel diagnostic procedure and the diagnosis of human ~ health. However,a major difference is that key indica- tors of human health, such as body temperature or Confinement blood chemistry, are well known, easily measured, and show relatively little variability among individu- .-CJ als. In contrast, the characteristics of healthy streams .c 0..- exhibit much greater spatial and temporal variability, a..>< are relatively poorly predicted with existing knowl- Valley OQ) material E- edge, and are much more difficult to measure (e.g., slope o~ Marcus et at., 1995). The interactions and feedbacks Q)o C)U betweencausal factors, when combinedwith the over- ° printed influence of the geographicregion and biogeo- m morphic context at the watershed and local scale,help Flow Riparian make the assessmentof stream channels a particular- obstructions vegetation ly difficult and complex task. Like a medical diagno- sis, a diagnostic channel assessmentmust synthesize a suite of observations, qualitative or quantitative Figure 1. Controls on Channel Morphology. models,and professionaljudgment to determine chan- nel condition and the probable cause of any degrada- tion. Hence, the application of a diagnostic approach The first phase in the suggesteddiagnostic proce- to channel assessmentand monitoring requires inde- dure is to define the system of interest and the con- pendent thinking and analysis, and personnel con- trolling variables. In the case of stream channel ducting the analysis must have both the requisite assessments,these steps include an evaluation of the training and the relevant experience to properly location within the channel network, channel type interpret their observationsof channel condition. and associatedcontrolling influences, temporal vari- Current practice in fluvial geomorphology stipu- ability in inputs, and historical conditions (Figure 2). lates that the diagnosis of physical channel condition Once this context has been established, the second include an evaluation of characteristics that are sen- phase usesfield observationsto evaluate various indi- sitive to changesin transport capacity (dischargefre- cators of channel condition. If these indicators are quency and magnitude), the amount and size of consistent, the diagnosis may be straightforward and sediment, type and density of riparian vegetation, have relatively little uncertainty. However, channel availability and abundanceof flow obstructions (e.g., diagnosis can be complicated by interactions among large woody debris and bedrock outcrops),geomorphic causal factors and conflicting or ambiguousindicators context (e.g., confinement and valley slope), and dis- of channel condition; such confusion can only be turbance history (Figure 1). An understanding of resolved through a combination of judgement and channel condition and potential responsedepends on additional observations. The following sections pro- an evaluation of the current and future influence of vide more specific guidanceto each of the steps in the each of the primary forcing factors (sediment load, diagnostic procedure. transport capacity, flow obstructions, and riparian vegetation)within the existing biogeomorphiccontext. Thus an assessmentof stream condition requires an Location in the Channel Network understanding of watershed as well as channel pro- cess~s.Ari assessmentof water quality and ecological The first step in the diagnostic procedure is to integrity requires an additional evaluation of stream define the reach(es) of interest and place them in chemistry and aquatic biota, but the discussion here will be restricted to the physical characteristics of regional, watershed, and local context. A given reach is subjected to both direct and indirect disturbances,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 3 JAWRA Montgomery and MacDonald including sediment inputs, peak flows, gravel or Channel1Ype and Controlling Influences placer mining, and changes in riparian vegetation. The type and effect of these disturbances will vary within a . Lane and Richards (1997: Differencesin channel behavior and responsehave 252) note that "understanding the behaviour of the long been recognized (Surell, 1841; Dana, 1850; reach cannot be divorced from consideration of its Shaler, 1891), and low-gradient differ from position within the catchment." In mountain drainage steep mountain channels in both morphologic basins, headwater channels are often subject to dis- response and the time for recovery from increased turbance by debris flows and high flows confined by sediment loading (Gilbert, 1917; Montgomery and valley walls, whereas lower-gradient alluvial chan- Buffington, 1998).Alluvial channels can respondin at nels tend to be subject to channel migration and avul- least seven ways to altered sediment supply or dis- sion as the primary disturbance processes(Swanson charge through changesin width, depth, slope, sinu- et al., 1988; Montgomery, 1999). The sequence of osity, bed surface grain size, roughness, and scour channel types also influences the interpretation of depth (Leopold and Maddock, 1953; Montgomery and expectedchannel conditions. A channel downstream Buffington, 1998). A number of workers have pro- from a large wetland or lake, for example, may be posed generic conceptual models of alluvial channel buffered from high flows or upstream sediment responseto changesin discharge or sediment supply inputs. Channel change resulting from severe (Gilbert, 1917; Lane, 1955; Schumm, 1971; Nunnally, disturbance in a headwater sub-catchment may 1985), but these approacheshave not explicitly con- diminish as materials propagate downstream (Bunte sidered how channel type alters channel response. and MacDonald, 1999). Hence proximity to sourcesor Montgomery and Buffington (1997) hypothesized sinks of sediment, water, or wood can all influence that different channel bed morphologiesreflect differ- channel condition and response. These spatial rela- ences in energy dissipation and relative transport tionships are an important part of the context needed capacity (i.e., the balance between transport capacity to diagnosethe condition of a particular reach. and sediment supply). Hence, differences in channel morphology imply differences in potential channel response.Montgomery and Buffington (1997) defined seven reach-level channel types based on the nature and organization of channel bed material: cascade, step-pool,plane-bed, pool-rifile, dune-ripple, colluvial, and bedrock. They also defined two alluvial channel types that are controlled by flow obstructions such as . wood debris (forced pool- channels and forced Determine channel types, step-poolchannels). controlling influences, and The classification of a reach by channel type is temporal variability in inputs based on readily-observedcharacteristics of bed mor- phology, and each channel type has different charac- teristics and potential responses (Montgomery and Buffington, 1998). However, channel type can change due to sustained or large magnitude variations in sed- iment supply, discharge, or riparian vegetation. Con- sequently, the contemporary channel type must be . interpreted in both a spatial context (i.e., valley slope and position within the watershed) and a temporal context (i.e., disturbance history). Other channel clas- sification systemscan also be used to interpret chan- nel sensitivity and response potential (e.g., Whiting . and Bradley, 1993; Rosgen, 1996), although not all systemswill be equally suited for a particular applica- tion. The key point is that the sequence of likely change and the sensitivity of different channel responsevariables will vary among channel types and Figure 2. Suggested Steps in the Channel Diagnostic Procedure. over different time scales.

JAWRA 4 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION Diagnostic Approach to Stream Channel Assessment and Monitoring

Temporal Variability in Inputs caused a sequenceof and incision (Costa, 1975), and the causesof such incision could easily be Large or sustained inputs of sediment or increases misinterpreted in the absenceof a broader historical in discharge may cause: or scour; context. changesin the size, volume, and number of habitat A variety of historical data may be available units (such as pools); altered channel dimensions; or for reconstructing past channel change in large even a change in channel type. Similarly, changesin streams or rivers. For these larger channels sequen- tial aerial photographs can be used to identify riparian vegetation may substantially influence chan- nel conditions, processes,and response. Some loca- changesin channel width, position and stability, tions are more prone to pulsed than chronic inputs, large wood loading, , canopy opening, and this variability in the magnitude and timing of and channel location. In small forest channels these inputs can affect both the interpretation of channel characteristics generally cannot be evaluated, but changeand the time scale of channel recovery.Large, canopy opening can be a useful surrogate for channel sustained inputs of sediment or changesin discharge width (Grant et al., 1984; Grant, 1988). As historical are more likely to have persistent impacts on channel aerial photographs generally do not extend back for conditions than pulsed inputs. In snownielt-dominat- more than 60 years, other qualitative and quantita- ed or -fed streams the flood-frequency curves tive sourcesof information must be used to put cur- are generally much flatter than for channels subject- rent channel condition into the broader context of ed to rain-on-snow events (MacDonald and Hoffman, longer-term trends. Smelser and Schmidt (1998) dis- 1995),and this will affect the range of conditions that cuss the use of data from stream gaging stations to might be observed.An extreme example of temporal assesshistorical changesin channel morphology. variability is the range of flows observed in arid regions. This greater variability in annual peak flows Changes in Riparian and Valley Bottom Vegetation will necessitate a more detailed assessmentof past events and is likely to complicate the diagnosis and monitoring of channel condition. Changes in valley bottom vegetation and beaver Channel networks in mountainous regions are also populations can strongly influence channel condition subject to tremendous variability in sediment inputs, and even channel type (Ryan, 1994; Busch and Smith, particularly if mass-wasting processesare an impor- 1995). For example, historical incision and entrench- tant sediment source.Headwater channelswill gener- ment of channelsin many areas of the western United ally be subject to greater temporal variability in States has been ascribed to trampling and overgraz- sediment inputs, while sediment routing processes ing of valley bottoms (Cookeand Reeves,1976). Valley will tend to dampen the amplitude of discrete input bottom and riparian vegetation can affect channelsby signals as the material propagates downstream altering flow resistance and bank strength, promoting through the channel network (Madej and Ozaki, 1996; local sedimentation, and providing a source of woody Bunte and MacDonald, 1999). Lack of bed-surface debris (Hupp, 1999). Consequently,changes in ripari- armoring is the norm for arid channels, whereas the an vegetation, such as those that can accompanylive- samecondition would suggesta high sediment load in stock introduction, may trigger channel change temperate streams. Hence,knowledge of the past and (Trimble and Mendel, 1995). Knowledge of the condi- potential disturbance frequency and magnitude is tion and changesin riparian vegetation often is need- important for interpreting channel condition and ed to assessand interpret the condition of a river or designinga monitoring program. stream relative to past and potential states.

Historical Conditions Field Observations and Indicators

An understanding of past conditions provides tem- Qualitative and quantitative observationsof select- poral context, and is a crucial step in both assessing ed attributes of the valley bottom and active channel current channel condition and defining a monitoring are the basis for a site-specific diagnosis of channel program. In many forested areas of the United States condition (Table 1). Pertinent channel attributes channelshave been subjectedto tie drives and splash reflect current and past sediment supply, transport (Sedell et al., 1991), and the continuing effect of capacity, flow obstructions, riparian vegetation, and these activities is often present but not always past disturbance. There is substantial. discretion in obvious (Massong and Montgomery, 2000). In the the detail and methods employed to characterize key southeastern U.S. historical agricultural practices features, as many channel characteristics are useful

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 5 JAWRA Montgomery and MacDonald

TABLE 1. Roleof Primary Field Indicators in DiagnosingChannel Condition

Field Indicators Role

Valley Bottom Characteristics

Slope Primary control on channel type and style of energy dissipation. Confmement Primary control on possible planform channel patterns. Entrenchment Indicates longer-term balance between runoff and sediment loads, and likely range of responses to high flows. Riparian Vegetation Primary control on channel characteristics. Overbank Deposits Indicates type and magnitude of recent deposits.

Active Channel Characteristics

Channel Pattern Braided channels imply high sediment loads, non-cohesive banks, or steep slopes. Large amounts ofLWD can also generate anastomosing channel form in lower-gradient channels Bank Conditions Location and extent of eroding bank relative to stream type can indicate level of recent disturbance. Gravel Bars Number, location, extent, and condition related to sediment supply. Pool Characteristics Distribution and amount of fme sediment deposition can indicate role of flow obstructions and whether sediment loads are high for a given channel type. Bed Material Size and distribution of surface and subsurface bed material can indicate relative balance between recent discharge and sediment supply. indicators of channel condition in only certain channel whether lateral migration is retarded by valley walls types or situations. The following sections discuss the or other impediments such as . Channel con- basis and criteria for interpreting key valley bottom finement is an important control on potential channel and active channel characteristics, and to illustrate response, as channels with wide may why a diagnostic approach is necessary and how it change their course, sinuosity, or planform in can be applied. responseto disturbance. Channels confined by valley walls are more limited in how they can respond to Valley Bottom Characteristics. Valley bottom disturbance. Hence, lateral confinement provides an attributes relevant to interpreting channel condition initial guide to the potential range of channel include slope, confinement, entrenchment, riparian response. vegetation, and overbank deposits. Taken together, valley bottom slope and confine- ment imply probable channel form and general Slope -Valley bottom slope is a key parameter for response potential, but do not usually indicate interpreting channel condition, as it largely deter- current stream condition (Montgomery and Buffing- mines the expectedchannel types. Since channel type ton, 1997; 1998). Current condition will vary due to can change in responseto changesin inputs, a com- factors such as the amount and role of woody debris, parison of the actual to expected bed morphology sediment supply, riparian vegetation, and the history should comeearly in the diagnostic process.This com- and legacies of past disturbances. Based on experi- parison is particularly important for understanding ence within a region, expectedchannel responsecan the role of controls on forced alluvial reaches.Valley be stratified by valley slope and confinement to help slope also can help determine what type of channel formulate hypotheses about channel processesthat should be expected in reaches that have become can be tested by field observations,and to extrapolate entrenched, channelized, or otherwise modified. For field analyses to other channel segments. More mountain drainage basins, a simple set of six gradient detailed, reach-level observations are needed to con- ranges is often sufficient to generally stratify moun- firm whether channels with similar gradients and tain channels «0.01, 0.01-0.02, 0.02-0.04, 0.04-0.08, confinement are likely to exhibit similar characteris- 0.08-0.20,>0.20). tics and similar responsesto changesin inputs.

Confinement -Channel confinement can be quanti- Entrenchment -Channel entrenchment is defined fled by the ratio of the valley bottom width to the by the elevation of the current relative to bankfull channel width. This ratio characterizes the elevation of the valley floor, with the floodplain

JAWRA 6 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION DiagnosticApproach to Stream Channel Assessmentand Monitoring defined as the area adjoining a river channel con- the channel that is largely unvegetated, at least for structed by the river in the present climate and over- some portion of the year, and inundated at times of flowed at times of high discharge (Leopold et at., high discharge.A number of active channel character- 1964). A channel is not entrenched when the flood istics can be used to infer relations among sediment plain and valley floor are approximately coincident. supply, transport capacity, and wood loading. These An entrenched channel is one where a small, active include the channel pattern, bank conditions, channel floodplain is isolated from the valley floor even during dimensions, distribution and extent of gravel bars, rare high-discharge events (Leopold et at., 1964). A pool characteristics, and bed material (Table 1). The moderately-entrenched channel has an active flood- interpretation of these indicators usually requires a plain that is inundated during moderately frequent comparison of existing condition with the condition discharge events, but the floodplain lies below a larg- expectedfor the same channel type in a comparable er terrace that is only rarely subjectedto flooding. geomorphic setting. Consequently, both experience In low-gradient valley segmentsthe floodplain ele- and objectivity are crucial for interpreting the vation should coincide with the valley floor unless observedcharacteristics of the active channel. there has been a changein inputs or external bound- ary conditions (e.g., base level). Steep channels may Channel Pattern -Channel pattern is closely relat- be incised through terraces composedof debris-flow ed to the amount and character of the available sedi- deposits,and in such casesthe entrenchment may not ment and transport capacity and, in some areas, the reflect recent channel disturbance. As with most influence of riparian vegetation (Leopoldet al., 1964). other indicators of channel condition, channel A downstream changein channel pattern from mean- entrenchment must be interpreted in the context of dering to braided, for example, may reflect an past disturbance and the geomorphicprocesses affect- extreme increase in sediment supply (Smith and ing a given reach. Smith, 1984). Downstream channel narrowing and an increase in stable, vegetated bars can indicate either Riparian Vegetation -The riparian vegetation is a a decreasein sediment supply or a decreasein dis- key indicator of channel condition. The type and charge (Patten, 1998). A change in channel type or amount of vegetation will directly affect bank stabili- sinuosity in sequential aerial photographs can indi- ty and influences channel processes through the input cate a significant change in sediment supply, trans- of woody debris and sediment from bank port capacity, riparian vegetation, or the supply of (Trimble, 1997). The type, age and spatial patterns of wood debris. For example, dredging and historical the riparian vegetation can indicate the nature and removal of wood from the Willamette River was asso- intensity of past disturbances (Rood and Mahoney, ciated with a change in the channel pattern from a 1990; Pat ten, 1998). complex anastamosing system to a single thread channel (Sedell and Froggatt, 1984). Changes in Overbank Deposits- and landslides are the channel pattern must be interpreted in the context of primary forms of catastrophic channel disturbance in channel processes,especially the complementary and forestedmountain drainage basins. These events typi- potentially competing effects of changesin discharge, cally erode material stored in steep channels (Costa, sediment supply, wood loading, and riparian vegeta- 1984)and deposit material in downstream, lower-gra- tion. dient channelswith a resultant effect on channel mor- phology and habitat characteristics (Everest and Bank Condition -The condition and form of the Meehan, 1981; Lamberti et at., 1991). The legacy of channel banks are important diagnostic characteris- such catastrophic events can dominate local channel tics, and the assessmentand interpretation of bank conditions, and these effects must be recognized in condition generally must be done in the field. Bank the diagnostic process.In particular, the presenceand erodibility and bank erosion are controlled by the nature of overbank deposits can indicate the type and channel type, location within the channel, history of magnitude of past disturbances. Key indicators high flows, bank material composition, and the include the presence oflog berms or sediment amount of bank protection offered by vegetation and deposits along channel margins, the approximate age wood debris. Qualitative descriptions of bank erosion and type of riparian vegetation, scour damage to can be strengthened by estimating the percentageof channel-margin vegetation, trash lines of debris the bank length undergoing active erosion, but the depositedby high flows, and flood or debris-flow lev- amount of bank erosion should be interpreted within ees. the context of the dominant channel-forming process- es and the bank material. Bare, eroding banks on the Active Channel Characteristics. The active outside of bends may be expected in pool- :hannel can be functionally defined as the portion of riffle channels. Extensive erosion on both channel

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 7 JAWRA Montgomery and MacDonald banks is uncommonbut can be expectedin some situ- 1978). Channel width generally increases with the ations, such as when a high-gradient channel cuts square root of the drainage area (Leopold and through unconsolidated . An increasing or Maddock, 1953; Montgomery and Gran, 2001), and unexpected amount of bank erosion can be due to depth increases as a power function of the drainage increased discharge or channel aggradation resulting area. However, there can be substantial local and from increased sediment supply. A reduction in the regional variability in these relationships. Reference integrity of riparian vegetation by fires, logging, or relationships should be developedfrom field measure- grazing can trigger bank erosion. Thus an under- ments in relatively undisturbed basins, but subtle standing of past watershed conditions is often needed changes are difficult to detect becauseof the scatter to interpret current bank conditions, and a diagnostic in such relationships due to channel type and local approachmust be applied becauseeroding banks can conditions. For example,logs can divert flow and alter be due to different causes,and the extent of eroding local bank stability, channel width (Trimble, 1997), banks may be disproportional to the magnitude of a and channel depth (Abbe and Montgomery, 1996). disturbance. Discrete episodes of scour and fill can alter width- depth ratios over relatively short time scales, while Gravel Bars -Gravel bars are sediment accumula- changesin watershed condition may result in larger- tions within the channel that are one or more channel scale and more persistent changesin channel dimen- widths long (Church and Jones, 1982). Bars typically sions. An understanding of the geomorphic context form where the is less than about and disturbance history is therefore necessaryto eval- 0.02 (Ikeda, 1975), and the bankfull width-to-depth uate the causesof local variability in channel dimen- ratio is greater than about 12 (Jaeggi, 1984).The size, sions, width-to-depth ratios, or hydraulic geometry. stability, and location of gravel bars can be a strong indicator of a changein sediment supply or transport Pool Characteristics -Pools may be formed by a capacity. For example, medial bars within a channel variety of processes involving interactions between or bar deposits on the outside of a meander bend can discharge and , and by local flow indicate an increase in sediment supply, a decreasein convergence forced by in-channel or bank obstruc- transport capacity, or both. Conversely,channel nar- tions. Pool frequency varies with channel type and rowing and an increase in bar stability -usually can be very sensitive to wood loading. Pools spaced caused by vegetation colonization -indicates a every five to seven channel widths are expected in decreasein sediment supply, a decrease in the fre- pool-riffle channels (Leopold et al., 1964); far fewer quency and magnitude of high flows, or both. The pools would be expected in plane-bed reaches (Mont- presenceand characteristics of gravel bars also may gomery and Buffington, 1997; 1998). In forest chan- reflect the broader context of the fluvial setting. nels, an average pool spacing of less than two channel Braided channels,for example, commonly form where widths characterizes forced pool-riffle channels with valley bottoms and channels widen downstream of high wood loading (Montgomery et al., 1995). In con- steep narrow valleys and .Gravel bar charac- trast, pool spacing in steeper step-pool channels is teristics, therefore, need to be interpreted according primarily a function of gradient rather than LWD to channel type, valley configuration, position in the loading (Montgomery et al., 1995; Rosgen, 1996; Wohl channel network, the nature of the bar-forcing mecha- et al., 1997). Hence a similar pool frequency may have nisms, and the historic condition of both the reaches very different interpretations depending upon chan- in question and their contributing watersheds. nel type and the amount of large, in-charrnel wood. Pool depth and pool volume are ecologically impor- Channel Dimensions -Stream channel width and tant characteristics that can vary with sediment load depth are often used for interpreting and monitoring and pool-forcing mechanism. Large increases in sedi- channel condition. Since wetted width and depth are ment load can reduce pool depth and pool volume discharge dependent, most people focus on bankfull (Megahan et al., 1980; Lisle, 1982), but pool depth can width and depth as assessedby surveyed cross sec- also reflect the mechanisms governing pool formation tions. Width-depth ratios are commonly calculated (Lisle, 1986). For example, field surveys in the Queets and used for channel classification (e.g., Rosgen River in Washington revealed that pools forced by sta- 1996), but these are very sensitive to the measured ble log jams or bedrock outcrops were deeper than depth and the location of the cross section. Bankfull pools formed by individual logs or freely formed by stage (Wolman and Leopold, 1957) often is presumed the interaction of flow and sediment transport (Abbe to represent the dominant discharge associatedwith and Montgomery, 1996). Hence, interpreting pool channel-forming events, but the identification of depth requires some knowledge of both local condi- bankfull width and depth is not always straightfor- tions and disturbance history. In addition, the sensi- ward, especially in mountain channels (Williams, tivity of pool depth to sedimentation may depend on

JAWRA 8 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION Diagnostic Approach to Stream Channel Assessment and Monitoring the nature of pool hydraulics, which dependsin turn Interpretation and Integration on the pool-forming agent. Because channel conditions result from a complex Bed Material -The size of particles on and below interplay of processes and causal factors, multiple the channel bed surface is sensitive to changes in the lines of evidence must be used to conduct a channel volume and size distribution of the sediment supply, assessment.Anyone indicator, or even a set ofindica- transport capacity, and abundance and size of wood tors, can mean different things according to the debris (Dietrich et al., 1989; Buffington and Mont- location in the channel network, channel type, and gomery, 1999a; 1999b). The generally coarser surface disturbance history. Channels are rarely subject to a layer, often referred to as an layer, provides single disturbance (MacDonald, 2000). Sorting shear resistance to flow at the channel bed, and mobi- through and interpreting the different processes, lization of the bed is controlled in part by the charac- causes,and indicators can be a complex and difficult teristics and size of the coarse surface layer. The task. Assessmentsmust begin with an understanding substrate under the surface armor represents the bed- of the dominant processesthat are operating in the load material transported by the channe! following channel, on the floodplain, and throughout the water- disruption of the surface layer (Parker et al., 1980). shed, consider the likely temporal variability in these The median grain size on the channel bed is a func- processes,develop hypotheses on how these processes tion of several factors, including discharge, sediment might be altered by management activities and natu- supply caliber and volume, and the hydraulic rough- ral events, and then make the initial field observa- ness provided by flow obstructions. Both an increase tions to support, dismiss, or modify these hypotheses. in basal shear stress and a reduction in sediment sup- A diagnostic approach, while not foolproof, is impor- ply can cause winnowing, and thereby a coarsening of tant because it provides a logical and minimally- the bed surface. Conversely, an increase in the supply biased framework for assessing channel condition. of fine sediment or a decrease in the size of high flows The exact steps will vary according to the issues of can lead to a reduction in the size of the particles on concern, but for alluvial stream channels the diagno- the bed surface. Higher wood loading provides greater sis can follow a systematic assessmentof the contex- hydraulic roughness which also favors a fining of the tual, valley bottom, and active channel attributes bed surface, whereas lower wood loading can decrease (Table 1). However, the analyst must also keep an hydraulic roughness and result in bed surface coars- open eye and open mind for other factors, characteris- ening (Buffington and Montgomery, 1999a). tics or influences that may be relevant to the channels The amount and location of fine sediment on the and watershed being assessed. channel bed provides additional diagnostic informa- tion. In some channel types the volume of fine sedi- ment overlying coarser material in pools can serve as an index of fine sediment supply (Lisle and Hilton, MONITORING 1992; 1999). Relatively small inputs of fine sediment will result in local deposits of sand and fine gravel in sheltered locations such as behind flow obstructions Monitoring means "to watch or check on," and mon- or large clasts. As the amount of fine sediment mov- itoring is used to assesschanges relative to an initial ing over the bed increases, these depositional sites condition. As such, monitoring is the logical follow up tend to expand downstream into elongated sand to test the veracity of channel diagnosesand evaluate stripes. At extremely high fine sediment loading, the channel responseto any changein managementiniti- entire channel may become buried by a blanket of fine ated as a result of the diagnosis.The interpretation of sediment. Hence the spatial distribution of fine sedi- an observed trend, or the lack of a trend, is greatly ment can indicate the relative magnitude of the fine strengthened by monitoring multiple sites that repre- sediment load, but the calibration of this indicator sent different levels of natural or anthropogenic dis- will vary with channel type and other factors such as turbance. The expected type and magnitude of the local geology (Schnackenberg and MacDonald channel response will also dictate the design of the 1998). The timing and magnitude of high flows must monitoring program. also be considered when interpreting bed material The present focus on channel characteristics stems grain-size data, as recent flow events can influence largely from the problems of directly measuring the degree of armoring and hence the grain-size dis- changesin sediment load, sediment supply, or size of tribution of the bed material. peak flows, let alone relating such change to a desig- nated use such as cold water fisheries (MacDonald et al., 1991). To detect an increase in sediment flux one must intensively sample during high flows, but the

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 9 JAWRA Montgomery and MacDonald high temporal variability and measurement uncer- the type and intensity of disturbance, and this under- tainties make it very difficult to statistically detect standing is critical to the design of a monitoring pro- even a moderatechange in sediment loads (Bunte and gram. For example,lower-gradient channels are likely MacDonald, 1995; 1999). Discharge, location on the to show pool infilling and substrate fining in response , and time since the last runoff event to an increased supply of fine sediment, while a explain only part of the observed variability in bed- unit increase in fine sediment supply to steep chan- load transport rates or suspended sediment concen- nels will generally have less effect on the bedforms or trations over any time scale (Walling and Webb, 1982; the bed material grain-size distributions due to the Carey, 1985; Beschta, 1987; Williams, 1989; Bunte higher transport capacity of these higher-gradient and MacDonald, 1999).The high interannual variabil- channels. These more obvious generalizations regard- ity of annual sediment loads means that many years ing channel responsemust then be modified or adjust- of monitoring are usually neededto detect significant ed according to factors such as the magnitude of the change (Loftis et at., 2001). A change in the size or likely increases in sediment loads or peak flows, the magnitude of peak flows is also difficult to detect size distribution of the additional sediment relative to except through a paired-watershed design, and this that of the local bed material, degree of bank protec- usually requires several years of calibration and post- tion, amount of large woody debris, influence of ripar- treatment data, respectively, as well as a substantial ian vegetation, and the time scale of the analysis. investment in personneland infrastructure. The response matrices presented in Tables 2 Monitoring more than one characteristic is recom- through 4 represent an attempt to characterize -by mended in order to provide a more comprehensive channel type -the relative sensitivity and direction of and a more reliable picture of channel behavior over channel response. Three forcing mechanisms are time. Becausemany of the issues in channel assess- explicitly considered:(1) a chronic increase in the sup- ment and monitoring are similar, a diagnostic ply of fine sediment; (2) a chronic increase in the sup- approachis neededto identify and interpret multiple ply of coarse sediment; and (3) an increase in the indicators of channel change. The following sections magnitude or duration of peak flows. Changesin the discuss the variables for monitoring as a function of type or condition of riparian vegetation are also channel type, forcing mechanism, and location within important but are too complexto be treated in a simi- the watershed. lar manner. We assume moderate and chronic increases in sediment supply or peak flows because more extreme or episodic increases could lead to dif- Selecting Variables for Monitoring ferent trends or more dramatic changes. For simplicity, the three forcing mechanisms are The site-specificinteractions betweenchannel type, evaluated independently despite the known interac- forcing mechanism, and channel response must be tions among peak flows, sediment supply, and sedi- understoodto select the variables for monitoring and ment transport. For the purpose of these tables, the design effectivemonitoring projects. Different channel change in peak flows is consideredto be a moderate types will exhibit differing responses to a given increase in the frequency or magnitude of the upper- changein sediment supply, the size of peak flows, or most 5 percent of the flow duration curve, as large riparian vegetation. The different characteristics of a flows typically transport most of the sediment load given channel type will also vary with respect to their (King, 1989; Troendle and Olsen, 1994). These larger propensity to change in responseto a given input or flows also initiate changes in channel morphology disturbance. Similarly, the direction and type of chan- that can alter the quality of fish habitat (Chamberlin nel response will vary according to the imposed et al., 1991). The problem is that an increase in the change in runoff, sediment loading, or other forcing magnitude of peak flows can trigger a confounding mechanism.When designing a monitoring project one increase in downstream sediment loads through bank must considerthe relative sensitivity of each channel erosion and channel scour (Madsen, 1994), and the characteristic by channel type, forcing mechanism, possibility of secondaryeffects and feedbacksneed to and biogeomorphiccontext. be considered when designing and implementing The design of a monitoring project to detect and monitoring projects. interpret channel change should be based on project The differentiation of channel response by forcing objectives,explicit predictions regarding which chan- mechanism and channel type is not necessarilytied to nel characteristics are likely to change,and an assess- a specific channel classification system. We choseto ment of which reaches are more or less prone to restrict our evaluation of channel responseto the five different responses. As discussed earlier, channel single-thread alluvial channel types defined by Mont- responsewill vary with channel type as well as with gomery and Buffington (1997). We grouped the chan- nel response variables into five categories: channel

JAWRA 10 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATIOI Diagnostic Approach to Stream Channel Assessment and Monitoring

TABLE 2. Relative Sensitivity of Alluvial Channel Types TABLE 3. Relative Sensitivity of Alluvial Channel Types to a Chronic Increase in the Supply of Coarse (>2 mm) to a Chronic Increase in the Supply of Fine ( < 2 mm) Sediment: .= very responsive; D = secondary or small Sediment: .= very responsive; D = secondary or small response; O = little or no response; -= not applicable. response; O = little or no response; -= not applicable. Channel types given by: C = cascade; SP = step-pool; Channel types given by: C = cascade; SP = step-pool; PB = plane-bed; PR = pool-rifl1e; and DR = dune-ripple. PB = plane-bed; PR = pool-riffie; and DR = dune-ripple.

ResponseVariables c SP PB PR DR ResponseVariables c SP PB PR DR Channel Dimensions Channel Dimensions

Bankfull Width D D . . D Bankfull Width o o o D D Bankfull Depth D D . . D Bankfull Depth 0 o o D D

Bed Material (particle size) Bed Material (particle size)

D84 O o . . . DS4 o o D D 0 DSO D o . . . D50 0 0 . . . DSO in Pools D . . o D16 D D . . 0 Percent Fines « 2 mm) 0 o o o o D50 in Pools D D . . Embeddedness 0 o 0 o o Percent Fines « 2 mm) D D . . Embeddedness D D . . Pool Characteristics Pool Characteristics Number - o - . D Area o . D Number - O o o Volume o . . D Area D - o o Residual Depth o . . D Volume O D . . v* 0 ~ 0 D Residual Depth D D . . V* D . Reach Morphology Reach Morphology Profiles/Bedforms O . o . O Bank Erosion D o o . D Thalweg Profiles o D o . D Habitat Units O o 0 . 0 Bank Erosion o 0 o O D Channel Scour D o . . D Habitat Units o 0 o D O Channel Scour o 0 o D D SedimentTransport SedimentTransport 0 0 0 0 o

Bedload . . . . o Suspended Load . . . . .

Bedload 0 0 0 D .

dimensions,bed material particle size, pool character- However,cascade channels are often at higher risk to istics, reach-scalemorphology, and bankfull sediment management-inducedlandslides and debris flows, and transport. Potential responses were rated for each these more extreme events can dramatically alter characteristic, channel type, and forcing mechanism these channels.We expectthat step-poolchannels will on a three-step qualitative scale: the channel charac- be more responsivethan cascadechannels, but overall teristic is very sensitive to changes in the forcing the projected response to moderate, chronic changes mechanism; a characteristic is moderately sensitive; in discharge and sediment supply will tend to be rela- and a characteristic is relatively insensitive to tively localized and small. An increase in the supply changesin the forcing mechanism. of coarse or fine sediment is more likely to be A review of Tables 2 through 4 shows considerable observedin the pools than on the steps or in the spac- variation among the five stream types and the ing and structure of bedforms. different channel characteristics in their expected Plane-bed channels are hypothesized to be more responseto an increase in sediment supply or the size responsive than step-pool channels with respect to of peak flows. Cascade channels are generally the changes in the bed material grain-size distribution. least sensitive to changesin discharge and sediment The magnitude of change in channel dimensions and supply becauseof their characteristically coarse bed bank erosion will depend on the resistance of the material, high transport capacity, and low sinuosity. banks and the degreeof confinement, but the absence

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1 JAWRA Montgomery and MacDonald of bedformslimits the number of channel characteris. bed material. In general, an increase in coarse sedi- tics available for monitoring. ment inputs should have a localized and persistent effect on the channel, whereas a pulse input of fine sediment will have an immediate effect on the bed material particle size that will rapidly dispersedown- TABLE 4. Relative Sensitivity of Alluvial Channel Types stream during higher flow events. to a Chronic Increase in the Frequency or Magnitude of Peak Flows: .= very responsive; O = secondary or small The amount of bank erosion in pool-riffie channels response; O = little or no response; -= not applicable. should be a relatively sensitive indicator of an Channel types given by: C = cascade; SP = step-pool; increase in the size of peak flows or coarse sediment PB = plane-bed; PR = pool-riffie; and DR = dune-ripple. inputs, and a less sensitive indicator of chronic, mod- erate increases in the amount of fine sediment. The ResponseVariables c SP PB PR DR infilling of pools in responseto an increasein fine sed- Channel Dimensions iment loads is considereda relatively sensitive chan- nel characteristic, and again this is supported by Bankfull Width D D . . . several field studies (Lisle and Hilton, 1992; 1999; Bankfull Depth D D . . . Madsen, 1994). A change in sediment supply or peak flows may also be expressedthrough changesin chan- Bed Material (particle size) nel dimensions, other pool characteristics, and reach

D84 o o 0 D o morphology, but these changes may not be as rapid D50 0 0 . . o and require a larger change in the forcing mecha- D16 D D . . o nisms. D50 in Pools D D . o As noted earlier, these ratings should be regarded Percent Fines ( < 2 mm) D D . . o as hypothesesbecause: (1) few studies have compared Embeddedness . . . . response by channel type; (2) local conditions will Pool Characteristics affect channel response; and (3) interactions among the forcing mechanisms and responsevariables oper- Number o o O o ate on a variety of temporal scales and complicate Area 0 0 D o actual channel response.We posit that these relative Volume D D . o rankings are broadly applicable and can guide moni- Residual Depth D D . o toring efforts, but further research is encouragedto V* D . o both test the hypothesized relationships and refine Reach Morphology the ideas presentedhere.

Thalweg Profiles O 0 0 . D Bank Erosion D . . . D Habitat Units O o 0 0 O DISCUSSION Channel Scour D o . . . SedimentTransport A diagnostic approach to channel assessmentand monitoring presents a marked contrast to the use of Suspended Load . . . . . check lists, score cards, or simple, uniform standards Bedload . . . . . such as percent pool area. Depending on the desired level of rigor, referencereaches are either explicitly or implictly needed to evaluate channel condition and trends. However, closely matched reference reaches In general, pool-riffle channels should have the are not always available, particularly for higher-order greatest sensitivity to increases in sediment supply streams. If comparable minimally-disturbed reaches or the size of peak flows. An early responseto either are not available, one may have to resort to more of these forcing mechanisms is likely to be a change qualitative comparisons,with a correspondingreduc- in the bed-surface grain-size distribution and/or tion in both the sensitivity and the certainty of the bank erosion, and this is supported by field studies results. Alternatively, one may evaluate channel con- (Bevenger and King, 1995; Schnackenberg and ditions against quantitative reference state models MacDonald, 1998). The direction of the shift in grain- that predict channel characteristics under specified size distribution will depend largely on: (1) the bal- conditions or assumptions(e.g., Buffington and Mont- ance between an increase in sediment supply and an gomery,1999a). increasein the size of peak flows; and (2) the size dis- The diagnostic approach to stream channel assess- tribution of the additional sediment relative to the ment has several distinct advantagesover more rigid

JAWRA 12 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION Diagnostic Approach to Stream Channel Assessment and Monitoring procedures. First, field personnel are compelled to both local and regional scales.Geomorphic theory and gather a more comprehensiveset of evidencein order field studies are essential for assessingchannel condi- to obtain and justify a diagnosis. Second,the diagnos- tions and identifying those channel characteristics tic approach attempts to understand the causes of and channel types that are most likely to exhibit sig- channel degradation rather than simply characterize nificant change in responseto a changein the supply the symptoms; the process of developing a channel of fine sediment, coarse sediment, or the size of peak diagnosis should provide valuable insight into flows. While we are hesitant to define a rigid diagnos- channel processesand watershed conditions (Thorne tic procedure, the diagnostic approach to channel et al., 1996; Downs and Thorne, 1996). Third, the assessment and monitoring provides a context and diagnostic approach is flexible and adaptable, and understanding that is needed to disentangle the this means that it is better able to respond to and rec- factors causing current channel condition, improve ognizeunique features or situations. When done well, the focus and sensitivity of monitoring efforts, and a diagnostic approach provides a structure, logic, and establish priorities for restoration. At a minimum, a focus to stream channel assessmentand monitoring. diagnostic channel assessment should address loca- If well documented,the resulting assessmentshould tion in the channel network, channel type, controlling be both clear and defensible. A fourth advantage of influences, temporal variability in inputs, and histori- the diagnostic approachis that it mandates the use of cal conditions. We have also identified key character- adequately trained and experienced specialists to istics of the valley bottom and the active channel that analyze a range of indicators to understand and inter- need to be evaluated in the field. Potential problems pret local channel processes.Finally, the diagnostic with a diagnostic approach include a potential for approach emphasizesthe need to look at the stream abuse or bias, the cost and effort needed to generate channel within the broader context of its watershed an accurate assessment,the potential for inadequate and geomorphicsetting. Thus the diagnostic approach and/or misleading diagnoses because of a lack of should help eliminate the tendency to futilely treat experienceor knowledge, institutional efforts to have the symptoms rather than the causes of channel standardized manuals proscribing assessment degradation. methodologies,and a dearth of appropriately trained There are several potential disadvantagesto using personnel. Nevertheless, we believe that a diagnostic a diagnostic approach. First, diagnosesare suscepti- approach is the best way to approach the complex ble to biasesin interpretation, or misrepresentation of problems associated with channel assessment and the certainty of the assessmentintroduced through monitoring. institutional cultures, budgets and priorities. Second, an accurate diagnosisrequires someadditional water- shed information, such as the history of disturbance ACKNOWLEDGMENTS and land use, in order to develop causal interpreta- tions of existing conditions and hypothesesfor future A number of organizations have sponsored the fieldwork and channel response. A third disadvantage is that the personal interactions which have led to this paper, and we would diagnostic approach requires experienced field per- like to acknowledge the support of the U.S. Forest Service, National Council of the Paper Industry for Air and Stream Improvement, sonnel trained beyond the level of workshops or short Washington State's Timber-Fish-Wildlife Program, and the Mon- courses, and a willingness to bring in additional tana Cumulative Effects Cooperative. The U.S. Environmental expertise when the diagnosis is particularly difficult Protection Agency supported further elaboration of the ideas dis- or either the implications or consequencesare partic- cussed in this paper. We also thank John Buff'mgton, Walt Mega- ularly important. Consequently,a significant impedi- han, Bill Dietrich, Peter Whiting, Kate Sullivan, and George Pess for their contributions to our thinking and the ideas expressed ment to widespread adoption of the diagnostic here, and three anonymous reviewers for their excellent sugges- approachto river channel assessmentis the need for tions on how to improve the manuscript. advanced training opportunities in river processes and diagnosis, as well as the design and implementa- tion of monitoring and restoration projects. LITERATURE CITED

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JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 13 JAWRA Montgomery and MacDonald

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American Fisheries Society Special Publica- Civil Engineers, New York, New York, pp. 380-395. tion 19:325-368. Montgomery, D. R., 1999. Process Domains and the River Continu- Shaler, N. S., 1891. The Origin and Nature of Soils. In: U.S. Geolog- um. Journal of the American Water Resources Association ical Survey 12th Annual Report, pp. 213-345. 35:397-410. Smelser, M. G. and J. C. Schmidt, 1998. An Assessment Methodolo- Montgomery, D. R., J. M. Buffmgton, R. D. Smith, K M. Schmidt, gy for Determining Historical Changes in Mountain Streams. and G. Pess. 1995. Pool Spacing in Forest Channels. Water USDA Forest Service Rocky Mountain Research Station RMRS- Resources Research 31:1097-1105. GTR-6, Fort Collins, Colorado, 29 pp. Montgomery, D. R. and J. M. Buffmgton, 1997. Channel Reach Mor- Smith, N. D. and D. G. Smith, 1984. William River: An Outstand- phology in Mountain Drainage Basins. Geological Society of ing Example of Channel. Widening and Braiding Caused by Bed- America Bulletin 109:596-611. Load Addition. Geology 12:78-82. Montgomery, D. R. and J. M. Buffmgton, 1998. Channel Processes, Surell, A., 1841. Etude sur les 'lbrrents des Hautes-Alpes. Dunot, Classification, and Response Potential. In: River Ecology and Paris, France. Management, R. J. Naiman, and R. E. Bilby (Editors). Springer- Swanson, F. J., T. K. Kratz, N. Caine, and R. G. Woodmansee, 1988. Verlag Inc., New York, New York, pp. 13-42. Landform Effects on Ecosystem Patterns and Processes. Bio- Montgomery, D. R. and K B. Gran, 2001. Downstream Variations Science 38:92-98. in the Width of Bedrock Channels. Water Resources Research Thorne, C. R., R. G. Allen, and A. Simon, 1996. Geomorphological 37:1841-1846. River Channel Reconnaissance for River Analysis, Engineering NRC (National Research Council), 1992. Restoration of Aquatic and Management. Transactions of the Institute of British Geog- Ecosystems: Science, Technology, and Public Policy. National raphers 21:469-483. Academy Press, Washington, D.C. Trimble, S. W., 1997. Stream Channel Erosion and Change Result- Nunnally, N. R., 1985. Application of Fluvial Relationships to Plan- ing from Riparian Forests. Geology 25:467-469. ning and Design of Channel Modifications. Environmental Man- Trimble, S. W. and A. C. Mendel, 1995. The Cow as a Geomorphic agement 9:417-426. Agent -A Critical Review. Geomorphology 13:233-253. Parker, G., P. C. Klingeman, and D. G. McLean, 1980. Bedload and Troendle, C. A. and W. K. Olsen, 1994. Potential Effects of Timber Size Distribution in Paved Gravel-Bed Streams. Journal of Harvest and Water Management on Streamflow Dynamics and Hydraulics Division, Proc. Am. Soc. Civ. Eng. 108:544-571. Sediment Transport. In: Sustainable Ecological Systems: Imple- Patten, D. T., 1998. Riparian Ecosystems of Semi-Arid North Amer- menting an Ecological Approach to Land Management, W. W. ica: Diversity and Human Impacts. Wetlands 18(4):498-512. Covington, and L. F. DeBano (Technical Coordinators.). USDA Paustian, S. J. et at. , 1992. A Channel Type Users Guide for the Forest Service General Technical Report RM -247 , Fort Collins, Tongass National Forest, Southeast Alaska. USDA Forest Ser- Colorado, pp. 34-41. vice Technical Paper R10-26, 179 pp. Walling, D. E. and B. W. Webb, 1982. Sediment Availability and the Pfankuch, D. J., 1975. Stream Reach Inventory and Channel sta- Prediction of Storm-Period Sediment Yields. In: Recent Develop- bility Evaluation. USDA Forest Service, Rl-75-002, 26 pp. ments in the Explanation and Prediction of Erosion and Sedi- Rood, S. B. and J.M. Mahoney, 1995. River Damming and Riparian mentYield. IAHS Publ. No.137, pp. 327-337. Cottonwoods Along the Marias River, Montana. Rivers 5(3):195- Ward, R. C., J. C. Loftis, and G. B. McBride, 1990. Design of Water 207. Quality Monitoring Systems. Van Nostrand Reinhold, New York, Rosgen, D., 1996. Applied River Morphology. Wildland Hydrology, New York, 231 pp. Pagosa Springs. Whiting, P. J. and J. B. Bradley, 1993. A Process-based Classifica- Ryan, S., 1994. Effects of Transbasin Diversions on Flow Regime, tion for Headwater Streams. Earth Surface Processes and Land- Bedload Transport, and Channel Morphology in Colorado Moun- forms 18:603-612. tain Streams. Ph.D. Dissertation, University of Colorado, Boul- Williams, G. P., 1978. Bank-Full Discharge of Rivers. Water der, Colorado. Resources Research 14:1141-1154. Sanders, T. G., R. C. Ward, J. C. Loftis, T. D. Steele, D. D. Adrian, Williams, G. P., 1989. Sediment Concentration Versus Water Dis- and V. Yevjevich, 1987. Design of Networks for Monitoring charge During Single Hydrologic Events in Rivers. Journal of Water Quality. Water Resources Publications, Littleton, Col- Hydrology 111:89-106. orado, 328 pp. Wohl, E. E., S. Madsen, and L. MacDonald, 1997. Characteristics of Log and Clast Bed-Steps in Step-pool Streams of Northwestern Montana, USA. Geomorphology 20:1-10.

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Wolman, M. G. and L. B. Leopold, 1957. River Flood Plains: Some Observations on their Formation. U.S. Geological Survey Profes- sional Paper 282-C, Washington, D.C. Ziemer, R. R., J. Lewis, R. M. Rice, and T. E. Lisle. 1991. Modeling the Cumulative Effects of Forest Strategies. Journal of Environ- mental Quality 20:36-42.

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