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J. N. Am. Benthol. Soc., 2005, 24(3):724–737� 2005 by The North American Benthological Society

BRIDGES

BRIDGES is a recurring feature of J-NABS intended to provide a forum for the interchange of ideas andinformation between basic and applied researchers in benthic science. Articles in this series will focus on topicalresearch areas and linkages between basic and applied aspects of research, monitoring, policy, and education.Readers with ideas for topics should contact Associate Editors Nick Aumen and Marty Gurtz.

Nick Aumen, nick�aumen@nps.govMarty Gurtz, megurtz@usgs.govCo-editors

Challenges and prospects for restoring urban streams: a perspectivefrom the Pacific Northwest of North America

DEREK B. BOOTH1

Center for Water and Watershed Studies, Box 352700, University of Washington,Seattle, Washington 98195 USA

Abstract. Undoing harm caused by catchment urbanization on stream channels and their residentbiota is challenging because of the range of stressors in this environment. One primary way in whichurbanization degrades biological conditions is by changing flow patterns; thus, reestablishing naturalflow regimes in urban streams demands particular attention if restoration is to have a chance forsuccess. Enhancement efforts in urban streams typically are limited to rehabilitating channel mor-phology and riparian habitat, but such physical improvements alone do not address all factors af-fecting biotic health. Some habitat-forming processes such as the delivery of woody debris or sedimentmay be amenable to partial restoration, even in highly disturbed streams, and they constitute obvioushigh-priority actions. There is no evidence to suggest, however, that improving nonhydrologic factorscan fully mitigate hydrologic consequences of urban development. In the absence of effective hydro-logic mitigation, appropriate short-term rehabilitation objectives for urban channels should be to 1)eliminate point sources of pollution, 2) reconstruct physical channel elements to resemble equivalentundisturbed channels, and 3) provide habitat for self-sustaining biotic communities, even if thosecommunities depart significantly from predisturbance conditions. Long-term improvement of streamconditions is not feasible under typical urban constraints, so large sums of money should not bespent on unrealistic or unreachable targets for stream rehabilitation. However, such a strategy shouldnot be an excuse to preclude potential future gains by taking irreversible present-day developmentor rehabilitative actions.

Key words: stream enhancement, urbanization, rehabilitation, restoration, watershed hydrology,aquatic invertebrates, land cover.

Catchment urbanization has long been knownto harm aquatic systems, but reversing the deg-radation imposed on the physical channel andresident biota remains elusive. Other papers inthis series focus on particular aspects of urbanstream degradation; my intent is to emphasizewhat may be needed to reduce such degrada-tion and to acknowledge constraints on success-ful restoration in urban catchments. Those con-straints are not well incorporated into manage-ment goals for urban streams; all too commonly,urban systems become orphans of neglect (i.e.,

1 E-mail address: dbooth@u.washington.edu

‘‘nothing can be done’’) or, conversely, of unre-alistic optimism (e.g., ‘‘the salmon will return’’).Review of recent studies, however, suggests thatother perspectives may be warranted that offerboth promising and achievable outcomes.

The context of my discussion is temperate,humid-region lowland streams where urban orsuburban development is the primary humandisturbance. Most of my examples are takenfrom the Puget Sound region of western Wash-ington, with the city of Seattle as the geographicand demographic center. The climate is mari-time and mild, with 75% of the annual rainfall(�1000 mm) falling in autumn and winter.

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FIG. 1. Five environmental features that are affected by urban development and, in turn, affect biologicalconditions in urban streams (from Booth et al. 2004, reprinted with permission of the American Water ResourcesAssociation; modified from Karr 1991, Karr and Yoder 2004).

Catchments in this region share relatively uni-form soil, climate, and topography, allowing di-rect comparisons among streams. All studystreams have, or once had, diverse natural biota,including anadromous salmonids; even streamsin moderately developed catchments still sup-port valuable biotic resources that are protectedby local, state, and/or federal laws, and arewidely appreciated by the public. State and localgovernment expenditures for stream enhance-ment have expanded dramatically over the pastdecade because of both legal requirements andpublic support, reflecting increased social andpolitical interest (National Marine Fisheries Ser-vice 2004, WDFW 2004).

Many human actions can disrupt the chemi-cal, physical, and biological processes that influ-ence stream biota. These processes, and their in-teractions, can be grouped into 5 classes of en-vironmental features (Fig. 1; Karr et al. 1986,Karr 1991, NRC 1992, Yoder and Rankin 1998).

This classification provides a tractable frame-work for analyzing the condition of water re-sources such that, when one or more environ-mental feature is affected by human activities,the result is ecosystem degradation. FollowingKarr (1999), biological conditions are judged aseither healthy or progressively less healthy com-pared with analogous reference conditions. Us-ing an endpoint of biological integrity acknowl-edges, but does not concede, the damage al-ready done by human intervention (cf. Rapportet al. 1998, Carpenter et al. 2003). However, noone environmental feature determines biologicalhealth a priori (Boulton 1999); conversely, im-proving any one feature does not guarantee im-provement in biotic condition of the catchmentas a whole.

Changes in the urban environment can be im-posed on any or all of the above features bymany human activities, through a number ofpathways at multiple spatial scales (Walsh et al.

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2005a). For example, changes in land cover in-tegrated over an entire catchment will alter bothstormwater inflows to streams and recharge ofgroundwater (Konrad et al. 2005). Adjacent tostream channels, changes to riparian land covercan affect localized input of energy from organ-ic matter and sunlight; at a single site, the struc-ture of the channel itself can be disrupted bydirect modification.

Any of the 5 features shown in Fig. 1 can beresponsible for reduced biological health in anurban stream, but changes in flow regimes, inparticular, are an important pathway by whichurbanization influences biotic conditions. Thispremise is based on the magnitude of change inhydrology commonly imposed by urbanization(Hollis 1975, Leopold 1968, Booth and Jackson1997, Konrad and Booth 2002) and the closeconnection between stream biological healthand hydrologic alteration (Power et al. 1988,Poff and Allan 1995, Resh et al. 1988, Poff andWard 1989, Horner and May 1999, Roy et al.2005). My focus on the hydrologic regime in thispaper should not imply that understanding hy-drology allows a complete explanation for ur-ban stream degradation; however, it does pro-vide a useful starting point for evaluatingstream-enhancement efforts in the Pacific North-west and, likely, for other humid-area regions ofthe world. Flow is a key factor in aquatic sys-tems and one that is almost universally alteredby urban development, so it demands particularattention if stream restoration is to have anychance of success.

Chemical water-quality alteration has re-ceived considerable attention in urban streams(Paul and Meyer 2001). However, data from allbut the most highly urbanized catchments in thePacific Northwest suggest no clear relationshipsbetween a broad suite of conventional water-chemical parameters and biological health (Mayet al. 1997, Horner and May 1999). Increases inconductivity and nutrients commonly are asso-ciated with increases in urbanization (May et al.1997, Herlihy et al. 1998, Walsh et al. 2005a) butcorresponding ecological effects are relativelyweak, closely correlated with hydrologic re-sponses, and generally cannot be explainedsolely in relation to chemical water-quality stan-dards.

The purpose of my paper is to review pastand ongoing studies in terms of 1) assessing theprevalence and importance of hydrologic alter-

ation in urban catchments, and 2) evaluating thenature and outcome of common enhancementapproaches in urban streams. In combination,these studies suggest a framework for ap-proaching urban stream restoration, in particu-lar one that recognizes not only the importanceof the hydrologic regime but also the uniqueconstraints of the urban environment on achiev-able goals and objectives for restoration.

Sources of Data

Relationships between urban land cover, bio-logical condition, and hydrology are evident inseveral studies across the Puget Lowland (seeBooth et al. 2004), with data collected from 45sites on 16 second- and third-order streams inKing and Snohomish counties. Streams havesimilar catchment areas (5–69 km2), local chan-nel gradients (0.4–3.2%), soils, elevation, and cli-mate typical of the central Puget Lowland, andurban development as the dominant human ac-tivity (American Forests 1998). Total impervi-ousness (TI, the % of a catchment covered byimpervious surfaces) was used to characterizedegree of urban development in the catchmentsdraining to each site; TI values were determinedfrom a classified 1998 Landsat image (30-m res-olution; Hill et al. 2003). Paved land cover in thecontributing catchments ranged from near 0 toalmost ⅔.

Benthic macroinvertebrate assemblages weresampled at all 45 sites from 1997 to 1999 (Mor-ley and Karr 2002). The biological condition ofeach site was quantified by the 10-metric benthicindex of biotic integrity (B-IBI, Karr 1998),which includes measures of taxon richness, tol-erance to disturbance, and selected ecologicalattributes (e.g., proportion of clingers and pred-ators). Hydrologic analyses were conducted atall of the macroinvertebrate sites that were closeto gauging stations and without intervening in-put of tributaries (n � 18 total sites; Konrad2000). Equivalent hydrologic analyses also wereconducted for 10 additional lowland streamswith similar gradients and catchment geology,but some with catchment areas up to 171 km2,to allow a more thorough assessment of the in-fluence of contrasting catchment urbanizationon flow regime.

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FIG. 2. Example of variation in the fraction of a year daily mean discharge exceeds annual mean discharge(TQmean) as a result of urban development, displayed with simulated hydrographs for Des Moines Creek in thecentral Puget Lowland (lat �47�24�N, long 122�20�W). Hydrographs and corresponding values of TQmean com-pare predevelopment (forested) condition for this 14-km2 catchment, current (degraded) condition, and fullcatchment urbanization with a hypothetical detention pond and high-flow bypass pipeline (preferred alterna-tive; estimated cost � $8 million US). Simulation results courtesy of King County Department of NaturalResources (King County 1997). Note that traditional hydrologic mitigation (i.e., preferred alternative) effectivelyreduces flood peaks, but its influence on TQmean values is significantly less pronounced.

Quantifying Hydrologic Alteration

Changing flow patterns over time scales ofmonths to years potentially imposes a long-term regime of frequent disturbances to streambiota (e.g., Pickett and White 1985, Poff et al.1997). In contrast, the long-term ecological con-sequences of a single 1- or 2-d flood are likelyto be unimportant because episodic high flowsare part of most riverine systems, irrespectiveof human disturbance. Published hydrologicstatistics that represent long-term storm andbaseflow patterns relevant to stream biota in-clude baseflow stability, daily discharge vari-ability, and spate frequency (Poff and Allan1995); the ratio of flood-to-baseflow volume, thefrequency of high flows, and the product of fre-quency and duration of high flows (Clausen andBiggs 1997); and the fraction of a year dailymean discharge exceeds annual mean discharge(TQmean) (Konrad and Booth 2002, Konrad et al.2005).

TQmean provides an intuitive index of urban in-fluence on flow regimes because it reflects theannual or decadal distribution of runoff be-tween storm flow and base flow. As such, it re-flects the degree of flashiness in a stream hy-drograph (Fig. 2). TQmean is expected to decreasewith urban development because annual meandischarge changes little in response to urbani-zation, whereas duration of individual floodpeaks shortens greatly (Konrad and Booth2005). This metric was used to characterize hy-drologic conditions in the study catchments be-cause of its demonstrated responsiveness to ur-banization.

The correlation of biological conditions (as B-IBI) with TQmean in the Puget Lowland studysites was about as good as with TI (R2 � 0.67for B-IBI vs TQmean, R2 � 0.70 for B-IBI vs TI, bothp � 0.001; Booth et al. 2004). However, TQmean isa more useful parameter than TI for under-standing degradation processes because it more

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closely represents a likely causal mechanism forstream degradation. TQmean is not a gross mea-sure of human disturbance, but instead express-es a disturbance signal for a specific environ-mental feature (e.g., Roy et al. 2003). Urbanstream degradation has multiple causes, but theconsistency of the B-IBI–TQmean relationship cou-pled with the ubiquity of hydrologic alterationin urban and urbanizing catchments (Booth andJackson 1997) suggest that hydrologic alterationis a fundamental determinant of biotic changesin these systems.

Historical Approaches to Restoring andRehabilitating Urban Streams

Goals for stream enhancement projects varyboth spatially and temporally. They are some-times articulated in terms of restoration, namelythe return to predisturbance conditions (Cairns1989). More typically, however, such goals offeronly the more modest objective of rehabilitation,the measurable improvement of a limited num-ber of elements, with the associated hope ofsome overall improvement in stream biologicalhealth. In either scenario, the focus is typicallyon the channel’s physical condition, with littleor no corresponding evaluation of the biologicalresponse. Yet, synoptic reviews and specific ex-amples both demonstrate the inadequacy ofphysical enhancement approaches alone.

Bethel and Neal (2003) noted the followingprevailing goals for stream-enhancement pro-jects in the Puget Sound region: ‘‘1. to establishthe channel morphology appropriate to the to-pographic, geologic, and hydrologic setting, and2. to establish the channel and riparian habitatthat support a diverse native plant and animalcommunity appropriate to the setting’’. Thisperspective was affirmed by most stream-en-hancement projects in the Puget Sound regionduring the 1990s (CUWRM 1998). Of the nearly400 stream-enhancement projects reviewed inCUWRM (1998), 90% fell into 4 broad categoriesinvolving physical rehabilitation: riparian en-hancement (planting and fencing; 35% of allprojects), instream habitat augmentation (largewoody debris [LWD] installation, gravel place-ment, and large rocks; 22%), bank stabilizationand grade control (18%), and fish passage en-hancement (15%). Each of these project catego-ries typically affects only a few tens to, at most,hundreds of meters of stream channel. The

CUWRM (1998) study also reported very lim-ited construction of flow-control projects such asregional detention ponds, presumably becauseof their high financial and environmental cost(e.g., King County 1994) and dubious effective-ness in hydrologic restoration (Booth and Jack-son 1997). In this context, Fig. 2 is an exampleof how very high project cost results in onlymodest hydrologic improvement. More integra-tive and potentially more effective flow-controlstrategies, notably low-impact development(LID; USEPA 2000) or the disconnection of im-pervious surfaces from the stream network(Walsh 2004, Walsh et al. 2005a), are poorly rep-resented by projects during this period(CUWRM 1998), although implementation isnow becoming more widespread (e.g., PugetSound Action Team 2003).

Despite the high abundance of stream-en-hancement projects, reported evaluations are re-markably limited, and available monitoring re-sults are not very encouraging (Beschta et al.1994, Kondolf and Micheli 1995). For example,Frissell and Nawa (1992) evaluated rates andcauses of physical impairment or failure for 161fish-habitat structures in 15 streams in south-west Oregon and southwest Washington. Theirstudy catchments generally had been affectedmore by logging rather than by urbanization,yet despite this generally less severe form ofcatchment disturbance, functional impairmentand outright project failure was common (me-dian damage rate � 60% following a singleflood, with a 2- to 10-y recurrence interval; Fris-sell and Nawa 1992). In particular, Frissell andNawa (1992) found that damage to restorationprojects was most widespread in streams withsigns of recent catchment disturbance, high sed-iment loads, and unstable channels. They ar-gued that restoration of alluvial streams withthe greatest potential for fish production in thePacific Northwest requires reestablishment ofnatural catchment and riparian processes ratherthan the construction of instream features. Lar-son et al. (2001) reviewed 6 projects in whichLWD was placed into small suburban and ur-ban streams and reported that these projectsproduced, at best, only modest changes in chan-nel structure but generally no improvement inbiological condition. Hession et al. (2003) re-ported that urban stream reaches with forestedriparian corridors in Pennsylvania and Dela-ware displayed differences in a few benthic

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macroinvertebrate metrics compared with non-forested sites, but only at the lowest levels ofcatchment TI. The common theme of these andother stream-restoration projects is their narrowsymptomatic focus (e.g., bank erosion or lack ofpools or LWD at a site) in response to an un-derlying disturbance at a much larger, typicallycatchment scale (e.g., logging or urbanization).

Anecdotal examples graphically demonstratethe challenges involved in restoring streams us-ing only symptomatic, local-scale approaches.Madsen Creek drains 6 km2 of largely urbanand suburban upland plateau in the Puget Low-land, �20 km southeast of Seattle. In 1989, thelowermost kilometer of the channel was relocat-ed as part of a road-widening and fish-enhance-ment project designed to recreate salmon-spawning habitat. The stated project objectivewas simply to deploy the specified quantities oflogs, stumps, riparian plants, and streambedgravel to the site. Logs and rootwads wereplaced in the channel, gravel of a size deemedsuitable for salmon spawning was spread overthe bed, and fast-growing native riparian spe-cies were planted along the banks (Fig. 3A). Alarge rainstorm that winter created significantflooding and erosion in the stream, and erosionof a steep ravine below the upland depositedhundreds of m3 of sand and silt throughout theproject reach that destroyed most of the con-structed habitat elements (Fig. 3B). Eight yearsof relatively benign flows later, the channel of-fers an instructive case both for and against site-scale rehabilitation (Fig. 3C): the riparian corri-dor is healthy and provides shade, litter, andprotection to the stream, but the large manmadestructures are either buried or eroded, and thechannel bed remains sandy, ill-suited for salm-on spawning, and reflects the sediment load ofthe upper catchment under present flow anderosion conditions. The project achieved only asubset of its goals, but not necessarily those ofgreatest concern or those that required the mostcostly actions.

Longfellow Creek, draining a heavily urban-ized catchment in Seattle, provides another ex-ample of a local-scale action motivated by broadecological goals but, at best, showing only mar-ginal success. In- and nearstream projects todate on a 2-km reach include removing fish-mi-gration barriers, planting riparian vegetation,reconstructing the channel, addition of spawn-ing gravel, and placement of instream LWD

(Fig. 4), for a cost of $8 million US. Post-resto-ration biotic conditions, however, have yieldedmassive pre-spawning death of returning (orstray) coho salmon (Seattle Post-Intelligencer2003), with only a small fraction of salmon sur-viving long enough to spawn, and with virtu-ally no smolt production (Fig. 5).

Consequences for Urban Stream Restoration

Habitat elements and habitat-building processes

The lessons of Madsen and Longfellow creeksand elsewhere are clear and should not be sur-prising. Certain instream conditions are easierto improve than others, but local actions cannotreverse the consequences of broadly degradedurban catchments. Given the financial and tech-nological obstacles to fixing catchment-scaledegradation, particularly hydrologic alteration,urbanization often promotes the inescapableconsequence of limiting efficacy of local-scaleactions (Barker et al. 1991, Booth and Jackson1997, Maxted and Shaver 1999, Booth et al. 2002,Morgan and Cushman 2005).

The difficulty in managing multiple scales ofdegradation has long been explored in forestry-dominated landscapes, where the distinctionbetween aquatic-habitat ‘‘elements’’ and habitat-building ‘‘processes’’ usefully discriminates theconstruction of channel features from the estab-lishment of self-sustaining improvements (Ced-erholm et al. 1997, Roni et al. 2002). For exam-ple, fish habitat in Pacific Northwest streams in-cludes such elements as LWD, pools, riparianand instream cover, gravel deposits, floodplains,and riparian vegetation. Each of these habitatelements can be built on-site, but neither theirlongevity (Frissell and Nawa 1992) nor their bi-ological effectiveness (Larson et al. 2001) can bedocumented. Roni and Quinn (2001) noted thatstreams subject to outmoded forest practicesand with initially low amounts of instreamwood generally showed the most dramatic in-creases in habitat quality and fish abundancefollowing local-scale LWD introductions. Thisoutcome is logical for channels where the ab-sence of LWD occurred primarily by physicalremoval (e.g., Collins et al. 2003). Yet, catchmentprocesses that create and must permanentlysupport such features (i.e., forest succession,sediment input, flow regime, geomorphic evo-lution of alluvial channels) operate at such broad

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FIG. 3. Reconstruction, disturbance, and partial recovery of lower Madsen Creek, southeast of Seattle, Wash-ington. Photographs taken September 1989 (A), February 1990 (B), and April 1998 (C).

FIG. 4. Longfellow Creek, in the city of Seattle, Washington, shortly after channel reconstruction with logdeflectors, imported channel-bed sediment, and riparian plantings.

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FIG. 5. Decline in survival at successive life stages of coho salmon in the 5 major streams of Seattle, Wash-ington (2003 data from the City of Seattle).

spatial and temporal scales that their productswill not persist if simply built or replaced(Kauffman et al. 1997, Roper et al. 1997, Beechieand Bolton 1999, Kondolf et al. 2001), particu-larly in flashy, unstable urban systems.

Short- and long-term enhancementof urban streams

This distinction between habitat elements andhabitat-building processes suggests an alterna-tive perspective to urban stream enhancement:short- vs long-term restoration activities. Theformer actions are generally feasible undermany different management settings but un-likely to produce permanent effects; they in-clude riparian fencing and planting, water-chemistry source control, fish-passage projects,use of instream structures, and construction ofsocial amenities. Short-term actions addressacute problems typical to stream channels in ur-ban and urbanizing catchments (Miltner et al.2004) and so are normally worthwhile, althoughthey only provide immediate solutions that arenecessary yet are insufficient to restore biotic in-tegrity.

Short-term actions also must acknowledge thepresence of people in urban environments. Ac-tions enhancing the quality of interactions be-tween people and urban streams, particularlythose justified in terms of quality of life or by

their value as a public amenity, are likely to besupported and maintained; indeed, such actionscommonly result in financial outlays far in ex-cess of likely ecosystem benefits (Middleton2001). Conversely, actions degrading or limitinginteractions between surrounding human com-munities and streams are more likely to fail.This situation is particularly relevant for short-term actions because they often are unlinked tocatchment processes and so typically requirecontinued maintenance to achieve even theirtransitory objectives. Use of public education toguide community actions in maintaining sus-tainable and ecologically beneficial streams andstream-enhancement projects is sorely needed(Purcell et al. 2002), which is a particular urgen-cy in the Pacific Northwest because most urbanstreams flow across private property and thuslie beyond the jurisdiction of public agencies(Schauman 2000).

In contrast, long-term actions are, by defini-tion, self-sustaining, and they address catch-ment processes at their relevant scales. However,they also must address each potentially degrad-ed environmental feature (Fig. 1) if they are toachieve enhanced biological health. Examplesinclude landuse planning such as preserves orzoning (King County 1994), avoiding road- andutility-stream crossings (Avolio 2003), rehabili-tating upland hydrology (e.g., stormwater rein-

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FIG. 6. Percent catchment imperviousness plotted against stream health (as benthic index of biotic integrity[B-IBI]) for Puget Lowland stream data. Management goals are commonly articulated for the upper right-handcorner of this graph (i.e., high-quality streams in highly urbanized watersheds), although no evidence suggeststhat this condition exists (modified from Booth et al. 2004; B-IBI data from Morley and Karr 2002).

filtration or LID; Walsh et al. 2005a), establish-ing riparian-zone vegetation communities, andreconnecting floodplains with their channels(Buffington et al. 2003).

Stewardship by the surrounding human com-munity is as important with long-term as withshort-term actions; however, it must emphasizeinstream biotic health over direct human inter-action with stream channels (Schauman and Sal-isbury 1998). A long-term focus on enhance-ment, therefore, tends to exclude people fromstream and riparian environments, even thoughenhancement requires social support to ensureecological success. There are few examples orcase histories to guide the development of thistask.

Despite good intentions, strong public inter-est, and massive funds, we have virtually noexamples of having achieved or retained bioticintegrity—i.e., ecological health akin to that inundisturbed streams—in degraded urban chan-nels. An example of this pattern comes fromstreams in the Puget Lowland (Morley and Karr2002), where catchment imperviousness plottedagainst stream health (as B-IBI) showed nohigh-quality streams in highly urbanized catch-ments (Fig. 6). Clearly, we have not yet devel-

oped nor implemented a truly effective stream-enhancement strategy, a failure that echoes along-recognized conclusion in ecological resto-ration regarding the challenge of achieving pre-disturbance ecosystem conditions in human-modified landscapes (Cairns 1989).

Towards better urban streams

The above perspective raises 2 key manage-ment questions for degraded urban catchments.First, can a natural flow regime ever be reestab-lished in an urban catchment and, if so, how?Second, if such a flow regime cannot be reestab-lished in urban catchments, what outcomesmight be expected from other management ac-tions that either construct short-term elementsor reestablish some long-term processes (e.g.,water-quality treatment, improved instreamhabitat, replanted riparian zone), but that do notaddress reestablishment of a natural flow re-gime?

A retrospective view suggests that the answerto the 1st management question is no, but failureof the last century’s management of hydrologicalteration should not condemn us to the samefuture. Instead, it merely emphasizes the need

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for new approaches to stormwater management,preferably those integrating multiple scales ofcatchment planning, site layout, and infrastruc-ture design. Such efforts are now beginningthroughout the world (e.g., Puget Sound ActionTeam 2003, Walsh et al. 2005a), although theireffectiveness is yet to be demonstrated. Deter-mining the optimal combination and resultingeffectiveness of such stormwater-managementstrategies should be a priority because theirpromise is great, alternatives are lacking, andconfirmatory data for design guidance are pres-ently sparse.

Yet full, or at least partial, long-term restora-tion of some habitat-forming processes, withsubsequent biological recovery, may be possibleeven in highly disturbed urban environments.Such restorative actions include controlling oflandslides and surface erosion to minimizechanges to sediment-delivery processes, pro-tecting mature riparian buffers to maintain de-livery of coarse and fine organic debris and tomoderate solar input (Jones et al. 1999, Parkynet al. 2003), and disconnecting the pipes linkingimpervious areas to natural channels (Walsh etal. 2004, 2005a, b). For example, a B-IBI increasefrom ‘‘very poor’’ to ‘‘fair’’ over �2 km along asingle suburban Puget Lowland stream channelwas strongly explained by riparian land coverbut not by overall catchment land cover (Morleyand Karr 2002). Avolio (2003) and McBride andBooth (2005) have documented good correla-tions between physical condition of channelsand frequency of stream-road crossings. Suchresults point to actions that are generally sen-sible to implement, even under existing man-agement constraints, because they are often eco-nomically feasible and may provide long-termbenefits. Furthermore, the absence of abruptthresholds in biological responses to urbaniza-tion (e.g., Booth et al. 2002, Morley and Karr2002) suggests that even incremental improve-ments can have direct, albeit commensuratelymodest, ecological benefits.

In the absence of effective hydrologic miti-gation, however, what are appropriate objectivesfor urban streams (e.g., see also Osborne et al.1993)? Point sources of pollution should beeliminated. In addition, channels should havethe same physical elements (e.g., pools, sub-strate, logs, accessible floodplains) as theirequivalent undisturbed counterparts, with therecognition that these elements are necessary

but not sufficient to support future biotic im-provements. Urban streams also should be con-sidered neighborhood amenities that inspirepassion and ownership from their nearby resi-dents, and they can be self-sustaining to bioticcommunities, even though those communitiesdepart significantly from predisturbance con-ditions.

Last, urban streams should also retain thepossibility, however remote, of one day benefit-ing from the long-term actions that can producegreater, sustainable improvements. This finalgoal cannot be achieved for most urbanizedcatchments under present socioeconomic con-structs, at least not in the Pacific Northwest. Thisconstraint should be a reminder not to spendlarge sums of money on targets that can neverbe reached by paths that are all-too-commonlyfollowed. This excuse is not sufficient, however,to continue building the kinds of urban devel-opments or traditional rehabilitation projectsthat permanently preclude future long-termstream improvements.

Acknowledgements

Much of the foundation for this discussionwas supported by the US Environmental Pro-tection Agency and National Science FoundationWater and Watersheds Program, EPA STARGrant R82-5284-010. Special thanks to membersof that research group, particularly James Karr,Christopher Konrad, Stephen Burges, SarahMorley, Sally Schauman, and Marit Larson. Ad-ditional support for this work came from theStormwater Technology Consortium of the Cen-ter for Water and Watershed Studies at the Uni-versity of Washington. Stephen J. Kropp com-piled the CUWRM (1998) data base of stream-enhancement projects; Seattle fish data wereprovided by Katherine Lynch and Laura Reedof Seattle Public Utilities. Suggestions from 2anonymous reviewers and the series editors,particularly Chris Walsh, substantially im-proved the content and clarity of the manu-script.

Literature Cited

AMERICAN FORESTS. 1998. Regional ecosystem analysis:Puget Sound metropolitan area. Final report. Amer-ican Forests, Washington, DC. (Available from:http://www.americanforests.org/downloads/rea/AF�PugetSound.pdf)

734 [Volume 24D. B. BOOTH

AVOLIO, C. M. 2003. The local impacts of road cross-ings on Puget Lowland creeks. MSCE Thesis, De-partment of Civil and Environmental Engineer-ing, University of Washington, Seattle, Washing-ton.

BARKER, B. L., R. D. NELSON, AND M. S. WIGMOSTA.1991. Performance of detention ponds designedaccording to current standards. Pages 64–70 inPuget Sound Research 91 Conference Proceed-ings. Puget Sound Water Quality Authority, Seat-tle, Washington.

BEECHIE, T., AND S. BOLTON. 1999. An approach to re-storing salmonid habitat-forming processes in Pa-cific Northwest watersheds. Fisheries 24(4):6–15.

BESCHTA, R. L., W. S. PLATTS, J. B. KAUFFMAN, AND M.T. HILL. 1994. Artificial stream restoration—mon-ey well spent or an expensive failure? Pages 76–104 in Proceedings of the Universities Council onWater Resources, Big Sky, Montana, 2–5 August1994. Universities Council on Water Resources,Carbondale, Illinois.

BETHEL, J., AND K. NEAL. 2003. Stream enhancementprojects: a King County perspective. Pages 394–421 in D. R. Montgomery, S. Bolton, D. B. Booth,and L. Wall (editors). Restoration of Puget Soundrivers. University of Washington Press, Seattle,Washington.

BOOTH, D. B., D. HARTLEY, AND C. R. JACKSON. 2002.Forest cover, impervious-surface area, and themitigation of stormwater impacts. Journal of theAmerican Water Resources Association 38:835–845.

BOOTH, D. B., AND C. R. JACKSON. 1997. Urbanizationof aquatic systems—degradation thresholds,stormwater detention, and the limits of mitiga-tion. Water Resources Bulletin 33:1077–1090.

BOOTH, D. B., J. R. KARR, S. SCHAUMAN, C. P. KONRAD,S. A. MORLEY, M. G. LARSON, AND S. J. BURGES.2004. Reviving urban streams: land use, hydrol-ogy, biology, and human behavior. Journal of theAmerican Water Resources Association 40:1351–1364.

BOULTON, A. J. 1999. An overview of river health as-sessment: philosophies, practice, problems, andprognosis. Freshwater Biology 41:469–479.

BUFFINGTON, J. M., R. D. WOODSMITH, D. B. BOOTH,AND D. R. MONTGOMERY. 2003. Fluvial processesin Puget Sound rivers in the Pacific Northwest.Pages 46–78 in D. R. Montgomery, S. Bolton, D. B.Booth, and L. Wall (editors). Restoration of PugetSound rivers. University of Washington Press,Seattle, Washington.

CAIRNS, J. 1989. Restoring damaged ecosystems: ispredisturbance condition a viable option? Envi-ronmental Professional 11:152–159.

CARPENTER, D. D., S. K. SINHA, K. BRENNAN, AND L.O. SLATE. 2003. Urban stream restoration. Journal

of Hydraulic Engineering—American Society ofCivil Engineers 129:491–493.

CEDERHOLM, C. J., R. E. BILBY, P. A. BISSON, T. W. BUM-STEAD, B. R. FRANSEN, W. J. SCARLETT, AND J. W.WARD. 1997. Response of juvenile coho salmonand steelhead to the placement of large woodydebris in a coastal Washington stream. Transac-tions of the American Fisheries Society 118:368–378.

CLAUSEN, B., AND B. J. F. BIGGS. 1997. Relationshipsbetween benthic biota and hydrologic indices inNew Zealand streams. Freshwater Biology 38:327–342.

COLLINS, B. D., D. R. MONTGOMERY, AND A. J. SHEIKH.2003. Reconstructing the historical riverine land-scape of the Puget Lowland. Pages 79–128 in D.R. Montgomery, S. Bolton, D. B. Booth, and L.Wall (editors). Restoration of Puget Sound rivers.University of Washington Press, Seattle, Washing-ton.

CUWRM (CENTER FOR URBAN WATER RESOURCES

MANAGEMENT). 1998. Washington Water Re-source—the quarterly report of the Center for Ur-ban Water Resources Management 9(4):4–50.(Available from: http://depts.washington.edu/cwws/Outreach/Publications/CUWRM newslet-ter/fall98.pdf)

FRISSELL, C. A., AND R. K. NAWA. 1992. Incidence andcauses of physical failure of artificial fish habitatstructures in streams of western Oregon andWashington. North American Journal of FisheriesManagement 12:182–197.

HERLIHY, A. T., J. L. STODDARD, AND C. B. JOHNSON.1998. The relationship between stream chemistryand watershed land cover data in the mid-Atlan-tic region, U.S. Water, Air, and Soil Pollution 105:377–386.

HESSION, W. C., D. D. HART, R. J. HORWITZ, D. A.KREEGER, D. J. VELINSKY, J. E. PIZZUTO, D. F.CHARLES, AND J. D. NEWBOLD. 2003. Riparian re-forestation in an urbanizing watershed: effects ofupland conditions on instream ecological bene-fits. Final report, EPA Grant Number R825798.US Environmental Protection Agency, Washing-ton, DC. (Available from:http://cfpub.epa.gov/ncer � abstracts / index . cfm / fuseaction / display.abstractDetail/abstract/182/report/F)

HILL, K. Z., E. BOTSFORD, AND D. B. BOOTH. 2003. Arapid land cover classification method for use inurban watershed analysis. Water Resources SeriesTechnical Report No. 173. Department of Civiland Environmental Engineering, University ofWashington, Seattle, Washington. (Available from:http://depts.washington.edu/cwws/Research/Reports/landcover03.pdf)

HOLLIS, G. E. 1975. The effect of urbanization onfloods of different recurrence interval. Water Re-sources Research 11:431–435.

2005] 735BRIDGES

HORNER, R. R., AND C. W. MAY. 1999. Regional studysupports natural land cover protection as leadingbest management practice for maintaining streamecological integrity. Pages 233–247 in Compre-hensive stormwater and aquatic ecosystem man-agement. First South Pacific Conference, Auck-land, New Zealand, 22–26 February 1999. NewZealand Water and Wastes Association, Auckland,New Zealand.

JONES, E. B. D., G. S. HELFMAN, J. O. HARPER, AND P.V. BOLSTAD. 1999. Effects of riparian forest re-moval on fish assemblages in southern Appala-chian streams. Conservation Biology 13:1454–1465.

KARR, J. R. 1991. Biological integrity: a long-neglectedaspect of water resource management. EcologicalApplications 1:66–84.

KARR, J. R. 1998. Rivers as sentinels: using the biologyof rivers to guide landscape management. Pages502–528 in R. J. Naiman and R. E. Bilby (editors).River ecology and management: lessons from thePacific coastal ecosystems. Springer, New York.

KARR, J. R. 1999. Defining and measuring river health.Freshwater Biology 41:221–234.

KARR, J. R., K. D. FAUSCH, P. L. ANGERMEIER, P. R.YANT, AND I. J. SCHLOSSER. 1986. Assessment ofbiological integrity in running waters: a methodand its rationale. Special Publication 5. IllinoisNatural History Survey, Urbana, Illinois.

KARR, J. R., AND C. O. YODER. 2004. Biological assess-ment and criteria improve TMDL planning anddecision making. Journal of Environmental En-gineering 130:594–604.

KAUFFMAN, J. B., R. L. BESCHTA, N. OTTING, AND D.LYTJEN. 1997. An ecological perspective of ripar-ian and stream restoration in the western UnitedStates. Fisheries 22(5):12–24.

KING COUNTY. 1994. Issaquah Creek Basin and non-point action plan. Surface Water Management Di-vision, Department of Public Works, Seattle,Washington. (Available from: King County Waterand Land Resources Division, 201 S. JacksonStreet, Seattle, Washington 98104 USA.)

KING COUNTY. 1997. Des Moines Creek basin plan.King County Department of Natural Resources,cities of SeaTac and Des Moines, and Port of Seat-tle, Seattle, Washington. (Available from: KingCounty Water and Land Resources Division, 201S. Jackson Street, Seattle, Washington 98104 USA.)

KONDOLF, G. M., AND E. R. MICHELI. 1995. Evaluatingstream restoration projects. Environmental Man-agement 19:1–15.

KONDOLF, G. M., M. W. SMELTZER, AND S. F. RAILS-BACK. 2001. Design and performance of a channelreconstruction project in a coastal Californiagravel-bed stream. Environmental Management28:761–776.

KONRAD, C. P. 2000. The frequency and extent of hy-

drologic disturbances in streams in the PugetLowland, Washington. PhD Thesis, University ofWashington, Seattle, Washington.

KONRAD, C. P., AND D. B. BOOTH. 2002. Hydrologictrends resulting from urban development inwestern Washington streams. Water-ResourcesInvestigation Report 02-4040. US Geological Sur-vey, US Department of the Interior, Washington,DC.

KONRAD, C. P., AND D. B. BOOTH. 2005. Hydrologicchanges in urban streams and their ecological sig-nificance. In L. R. Brown, R. H. Gray, R. M.Hughes, and M. R. Meador (editors). Effects ofurbanization on stream ecosystems. Symposium47. American Fisheries Society, Bethesda, Mary-land (in press).

KONRAD, C. P., D. B. BOOTH, AND S. J. BURGES. 2005.Effects of urban development in the Puget Low-land, Washington on interannual streamflow pat-terns: consequences for channel form and stream-bed disturbance. Water Resources Research 41,W07009, doi:10.1029/2005WR004097.

LARSON, M. L., D. B. BOOTH, AND S. M. MORLEY. 2001.Effectiveness of large woody debris in stream re-habilitation projects in urban basins. EcologicalEngineering 18:211–226.

LEOPOLD, L. B. 1968. Hydrology for urban land plan-ning: a guidebook on the hydrologic effects of ur-ban land use. Geological Survey Circular 554. USGeological Survey, US Department of the Interior,Washington, DC.

MAXTED, J. R., AND E. SHAVER. 1999. The use of detentionbasins to mitigate stormwater impacts to aquatic life.Pages 6–15 in National Conference on Retrofit Op-portunities for Water Resource Protection in UrbanEnvironments, Chicago, Illinois, 9–12 February 1998.EPA/625/R-99/002. Office of Research and Devel-opment, U.S. Environmental Protection Agency,Washington, DC. (Available from http://www.epa.gov/nrmrl/pubs/625r99002/625r99002.htm)

MAY, C. W., E. B. WELCH, R. R. HORNER, J. R. KARR,AND B. W. MAR. 1997. Quality indices for urban-ization effects in Puget Sound lowland streams.Water Resources Series Technical Report No. 154.Urban Water Resources Center, Department ofCivil Engineering, University of Washington,Seattle, Washington.

MCBRIDE, M., AND D. B. BOOTH. 2005. Urban impactson physical stream conditions: effects of spatialscale, connectivity, and longitudinal trends. Jour-nal of the American Water Resources Association41:565–580.

MIDDLETON, J. V. 2001. The stream doctor project:community-driven stream restoration. BioScience4:293–296.

MILTNER, R. J., D. WHITE, AND C. YODER. 2004. Thebiotic integrity of streams in urban and subur-

736 [Volume 24D. B. BOOTH

banizing landscapes. Landscape and Urban Plan-ning 69:87–100.

MORGAN, R. P., AND S. F. CUSHMAN. 2005. Urbaniza-tion effects on stream fish assemblages in Mary-land, USA. Journal of the North American Ben-thological Society 24:643–655.

MORLEY, S. A., AND J. R. KARR. 2002. Assessing andrestoring the health of urban streams in the PugetSound basin. Conservation Biology 16:1498–1509.

NATIONAL MARINE FISHERIES SERVICE. 2004. Pacific coast-al salmon recovery fund. Northwest Regional Office,National Marine Fisheries Service, Seattle, Washing-ton. (Availablefrom:http://webapps.nwfsc.noaa.gov/servlet/page?�pageid�1306&�dad�portal30&�

schema�PORTAL30)NRC (NATIONAL RESEARCH COUNCIL). 1992. Restora-

tion of aquatic ecosystems: science, technology,and public policy. National Academy Press,Washington, DC.

OSBORNE, L. L., P. B. BAYLEY, L. W. G. HIGLER, B.STATZNER, F. TRISKA, AND T. M. IVERSEN. 1993.Restoration of lowland streams—an introduction.Freshwater Biology 29:187–194.

PARKYN, S. M., R. J. DAVIES-COLLEY, N. J. HALLIDAY,K. J. COSTLEY, AND G. F. CROKER. 2003. Plantedriparian buffer zones in New Zealand: do theylive up to expectations? Restoration Ecology 11:436–447.

PAUL, M. J., AND J. L. MEYER. 2001. Streams in theurban landscape. Annual Review of Ecology andSystematics 32:333–365.

PICKETT, S. T. A., AND P. S. WHITE (EDITORS). 1985. Theecology of natural disturbance and patch dynam-ics. Academic Press, New York.

POFF, N. L., AND J. D. ALLAN. 1995. Functional orga-nization of stream fish assemblages in relation tohydrologic variability. Ecology 76:606–627.

POFF, N. L., J. D. ALLAN, M. B. BAIN, J. R. KARR, K. L.PRESTEGAARD, B. D. RICHTER, R. E. SPARKS, AND

J. C. STROMBERG. 1997. The natural flow regime:a paradigm for river conservation and restoration.BioScience 47:769–784.

POFF, N. L., AND J. V. WARD. 1989. Implications ofstreamflow variability and predictability for loticcommunity structure: a regional analysis ofstreamflow patterns. Canadian Journal of Fisher-ies and Aquatic Sciences 46:1805–1818.

POWER, M. E., R. J. STOUT, C. E. CUSHING, P. P. HARPER,F. R. HAUER, W. J. MATTHEWS, P. B. MOYLE, B.STATZNER, AND I. R. WAIS DE BADGEN. 1988. Bi-otic and abiotic controls in river and stream com-munities. Journal of the North American Ben-thological Society 7:456–479.

PUGET SOUND ACTION TEAM. 2003. Natural approach-es to stormwater management. Puget Sound Ac-tion Team, Olympia, Washington. (Availablefrom: http:// www. psat. wa. gov / Publications /LID�studies/lid�natural�approaches.pdf)

PURCELL, A. H., C. FRIEDRICH, AND V. H. RESH. 2002.An assessment of a small urban stream restora-tion project in northern California. RestorationEcology 10:685–694.

RAPPORT, D. J., C. GAUDET, J. R. KARR, J. S. BARON, C.BOHLEN, W. JACKSON, B. JONES, R. J. NAIMAN, B.NORTON, AND M. M. POLLOCK. 1998. Evaluatinglandscape health: integrating societal goals andbiophysical process. Journal of EnvironmentalManagement 53:1–15.

RESH, V. H., A. V. BROWN, A. P. COVICH, M. E. GURTZ,H. W. LI, G. W. MINSHALL, S. R. REICE, A. L. SHEL-DON, J. B. WALLACE, AND R. C. WISSMAR. 1988.The role of disturbance in stream ecology. Journalof the North American Benthological Society 7:433–455.

RONI, P., T. J. BEECHIE, R. E. BILBY, F. E. LEONETTI, M.M. POLLOCK, AND P. R. PESS. 2002. A review ofstream restoration techniques and a hierarchicalstrategy for prioritizing restoration in PacificNorthwest watersheds. North American Journalof Fisheries Management 22:1–20.

RONI, P., AND T. P. QUINN. 2001. Density and size ofjuvenile salmonids in response to placement oflarge woody debris in western Oregon and Wash-ington streams. Canadian Journal of Fisheries andAquatic Sciences 58:282–292.

ROPER, B. B., J. J. DOSE, AND J. E. WILLIAMS. 1997.Stream restoration: is fisheries biology enough?Fisheries 22(5):6–11.

ROY, A. H., M. C. FREEMAN, B. J. FREEMAN, S. J. WEN-GER, W. E. ENSIGN, AND J. L. MEYER. 2005. Inves-tigating hydrological alteration as a mechanism offish assemblage shifts in urbanizing streams.Journal of the North American Benthological So-ciety 24:656–678.

ROY, A. H., A. D. ROSEMOND, M. J. PAUL, D. S. LEIGH,AND J. B. WALLACE. 2003. Stream macroinverte-brate response to catchment urbanisation (Geor-gia, U.S.A.). Freshwater Biology 48:329–346.

SCHAUMAN, S. 2000. Human behavior in urban ripar-ian corridors. Pages 335–340 in International Con-ference on Riparian Ecology and Management inMulti-Land Use Watersheds, Portland, Oregon,28–31 August 2000. American Water ResourcesAssociation, Middleburg, Virginia.

SCHAUMAN, S., AND S. SALISBURY. 1998. Restoring na-ture in the city: Puget Sound experiences. Land-scape and Urban Planning 42:287–295.

SEATTLE POST-INTELLIGENCER. 2003. Our troubledsound: spawning coho are dying early in restoredcreeks. 6 February 2003. (Available from: http://seattlepi. nwsource. com / local / 107460� coho06.shtml?searchpagefrom�1&searchdiff�394)

USEPA (US ENVIRONMENTAL PROTECTION AGENCY).2000. Low impact development: a literature re-view. EPA-841-B-00-005. Office of Water, US En-vironmental Protection Agency, Washington, DC.

2005] 737BRIDGES

(Available from: http://www.epa.gov/owow/nps/lid/lid.pdf)

WALSH, C. J. 2004. Protection of in-stream biota fromurban impacts: minimise catchment impervious-ness or improve drainage design? Marine andFreshwater Research 55:317–326.

WALSH, C. J., T. D. FLETCHER, AND A. R. LADSON.2005a. Stream restoration in urban catchmentsthrough redesigning stormwater systems: lookingto the catchment to save the stream. Journal of theNorth American Benthological Society 24:690–705.

WALSH, C. J., P. J. PAPAS, D. CROWTHER, P. T. SIM, AND

J. YOO. 2004. Stormwater drainage pipes as athreat to a stream-dwelling amphipod of conser-vation significance, Austrogammarus australis, insoutheastern Australia. Biodiversity and Conser-vation 13:781–793.

WALSH, C. J., A. H. ROY, J. W. FEMINELLA, P. D. COT-TINGHAM, P. M. GROFFMAN, AND R. P. MORGAN.2005b. The urban stream syndrome: currentknowledge and the search for a cure. Journal of

the North American Benthological Society 24:706–723.

WDFW (WASHINGTON DEPARTMENT OF FISH AND

WILDLIFE). 2004. Washington State regional fish-eries enhancement groups—eight-year outcomesand accomplishments. Washington Departmentof Fish and Wildlife, Olympia, Washington.(Available from: http://wdfw.wa.gov/volunter/rfeg/rfeg2004.pdf)

YODER, C. O., AND E. T. RANKIN. 1998. The role ofbiological indicators in a state water quality man-agement process. Environmental Monitoring andAssessment 51:61–88.

About the Author

Derek Booth is a geologist and research professorat the University of Washington. He studies the caus-es of stream-channel degradation and the effectivenessof stormwater mitigation, in collaboration with manytalented colleagues.