wr- systems planning & mmt - 15_appendix_a

8/2/2019 WR- Systems Planning & Mmt - 15_appendix_a

1/78

Appendix A: Natural System Processes and Interactions

1. Introduction 483

2. Rivers 483

2.1. River Corridor 484

2.1.1. Stream Channel Structure Equilibrium 485

2.1.2. Lateral Structure of Stream or River Corridors 486

2.1.3. Longitudinal Structure of Stream or River Corridors 487

2.2 Drainage Patterns 488

2.2.1. Sinuosity 489

2.2.2. Pools and Riffles 489

2.3. Vegetation in the Stream and River Corridors 489

2.4. The River Continuum Concept 490

2.5. Ecological Impacts of Flow 490

2.6. Geomorphology 490

2.6.1. Channel Classification 491

2.6.2. Channel Sediment Transport and Deposition 4912.6.3. Channel Geometry 493

2.6.4. Channel Cross Sections and Flow Velocities 494

2.6.5. Channel Bed Forms 495

2.6.6. Channel Planforms 495

2.6.7. Anthropogenic Factors 496

2.7. Water Quality 497

2.8. Aquatic Vegetation and Fauna 498

2.9. Ecological Connectivity and Width 500

2.10. Dynamic Equilibrium 501

2.11. Restoring Degraded Aquatic Systems 501

3. Lakes and Reservoirs 504

3.1. Natural Lakes 504

3.2. Constructed Reservoirs 505

3.3. Physical Characteristics 505

3.3.1. Shape and Morphometry 505

3.3.2. Water Quality 506

3.3.3. Downstream Characteristics 507

3.4. Management of Lakes and Reservoirs 508

3.5. Future Reservoir Development 510

4. Wetlands 5104.1. Characteristics of Wetlands 511

4.1.1. Landscape Position 512

4.1.2. Soil Saturation and Fibre Content 512

4.1.3. Vegetation Density and Type 512

4.1.4. Interaction with Groundwater 513

4.1.5. OxidationReduction 513

4.1.6. Hydrological Flux and Life Support 513

WATER RESOURCES SYSTEMS PLANNING AND MANAGEMENT ISBN 92-3-103998-9 UNESCO 2005


2/78

4.2. Biogeochemical Cycling and Storage 513

4.2.1. Nitrogen (N) 514

4.2.2. Phosphorus (P) 514

4.2.3. Carbon (C) 514

4.2.4. Sulphur (S) 514

4.2.5. Suspended Solids 514

4.2.6. Metals 5154.3. Wetland Ecology 515

4.4. Wetland Functions 515

4.4.1. Water Quality and Hydrology 515

4.4.2. Flood Protection 516

4.4.3. Shoreline Erosion 516

4.4.4. Fish and Wildlife Habitat 516

4.4.5. Natural Products 516

4.4.6. Recreation and Aesthetics 516

5. Estuaries 516

5.1. Types of Estuaries 5175.2. Boundaries of an Estuary 518

5.3. Upstream Catchment Areas 519

5.4. Water Movement 519

5.4.1. Ebb and Flood Tides 519

5.4.2. Tidal Excursion 520

5.4.3. Tidal Prism 520

5.4.4. Tidal Pumping 520

5.4.5. Gravitational Circulation 520

5.4.6. Wind-Driven Currents 521

5.5. Mixing Processes 521

5.5.1. Advection and Dispersion 522

5.5.2. Mixing 522

5.6. Salinity Movement 523

5.6.1. Mixing of Salt- and Freshwaters 523

5.6.2. Salinity Regimes 523

5.6.3. Variations due to Freshwater Flow 523

5.7. Sediment Movement 524

5.7.1. Sources of Sediment 524

5.7.2. Factors Affecting Sediment Movement 524

5.7.3. Wind Effects 525

5.7.4. Ocean Waves and Entrance Effects 5255.7.5. Movement of Muds 526

5.7.6. Estuarine Turbidity Maximum 527

5.7.7. Biological Effects 527

5.8. Surface Pollutant Movement 528

5.9. Estuarine Food Webs and Habitats 528

5.9.1. Habitat Zones 529



3/78

5.10. Estuarine Services 531

5.11. Estuary Protection 531

5.12. Estuarine Restoration 533

5.13. Estuarine Management 533

5.13.1. Engineering Infrastructure 534

5.13.2. Nutrient Overloading 534

5.13.3. Pathogens 5345.13.4. Toxic Chemicals 534

5.13.5. Habitat Loss and Degradation 534

5.13.6. Introduced Species 535

5.13.7. Alteration of Natural Flow Regimes 535

5.13.8. Declines in Fish and Wildlife Populations 535

6. Coasts 535

6.1. Coastal Zone Features and Processes 535

6.1.1. Water Waves 536

6.1.2. Tides and Water Levels 538

6.1.3. Coastal Sediment Transport 5386.1.4. Barrier Islands 538

6.1.5. Tidal Deltas and Inlets 538

6.1.6. Beaches 538

6.1.7. Dunes 539

6.1.8. Longshore Currents 540

6.2. Coasts Under Stress 540

6.3. Management Issues 540

6.3.1. Beaches or Buildings 542

6.3.2. Groundwater 542

6.3.3. Sea Level Rise 542

6.3.4. Subsidence 543

6.3.5. Wastewater 544

6.3.6. Other Pollutants 544

6.3.7. Mining of Beach Materials 545

6.4. Management Measures 545

6.4.1. Conforming Use 546

6.4.2. Structures 546

6.4.3. Artificial Beach Nourishment 547

7. Conclusion 548

8. References 549



4/78

1. Introduction

The hydrological, geomorphological, environmental andecological state of streams and rivers, and of their down-

steam estuaries and coasts, are indicators of past andcurrent management policies or practices. The conditionof a stream, river, estuary or coast is an indicator of howwell it, as a system, can function. Natural systems canfilter contaminants from runoff; store, absorb and gradu-ally release floodwaters; serve as habitat for fish andwildlife; recharge groundwater; provide for commercialtransport of cargo; become sites for hydropower; andprovide recreational opportunities beneficial to humans.Degraded systems do not perform these functions as wellas non-degraded systems.

Today the importance of keeping natural aquaticsystems alive and well, diverse and productive, in addi-tion to meeting the needs of multiple economic and socialinterests, is much better appreciated and recognized thanit was when water resources planners and managers wereinvolved in conquering nature and taming its variabili-ties. Natural system restoration and sustainability havebecome major management objectives, along with themaintenance of the usual economic services that water

Natural System Processesand Interactions

Understanding the natural processes as well as the economic and social services

or functions that rivers, lakes, reservoirs, wetlands, estuaries and coasts fulfill is

critical to the successful and sustainable management of these hydrological

systems. These natural processes involve numerous physical and biological

interactions that take place among the components of fluvial systems and their

adjacent lands. This appendix briefly views some of the important natural

processes and interactions that occur in watersheds, river basins, estuaries and

coasts. Those who manage them should be aware of these processes andinteractions as they build and use their models to analyse, plan and evaluate

alternative management policies and practices.

Appendix A:

and related land management can provide. Satisfyingthese objectives as far as possible requires an understaing of the basic hydrological, geological, environmeand ecological interactions that take place in nat

aquatic systems.This appendix is divided into five main sections. next section will focus on rivers. It is followed by sectdescribing lakes and reservoirs, wetlands, estuaries, finally coasts. Multiple books have been written on eof these water resources system components. Whapresented in this appendix is thus only an outline ofmain features of these water bodies and how they canmanaged. Its purpose is to introduce some vocabuand serve as a primer for those not familiar with this baground information.

2. Rivers

Rivers are driven by hydrological, fluvial, geomorpholowater quality and ecological processes that occur ovrange of temporal and spatial scales. The plant and anicommunities in rivers and their floodplains are dependupon change: changing flows, moving sediments



5/78

shifting channels. They depend on inputs of organicmatter from vegetation in the riparian zone. They dependon the exchange of nutrients, minerals, organic matterand organisms between the river and its floodplain. Thisis provided by variable flows and sediment transport. Allof these factors influence the structural character of thestream or river and its aquatic and terrestrial ecosystems their species distribution, diversity and abundance.

Assessments of the effect of human activities on riversystems require indicators relating cause to effect. Acauseeffect chain is illustrated in Figure A.1. Insight into

connections between processes and structures and theirtemporal and spatial scales leads to a more integratedinterdisciplinary approach to river system monitoring andmanagement.

2.1. River Corridor

A river corridor can be viewed as a hierarchical seriesof river segments, from upstream headwater streamsto large downstream rivers, as illustrated in Figure A.2.River corridors include the river channels and the river

margins (the waterland interfaces), and both are influencedby surface watergroundwater interactions. These environ-ments are characterized by hydrological, geomorphological,environmental and ecological interactions. River margininteractions influence surrounding terrestrial landscapes.

Features that influence the structure and functioningof river systems occur at various spatial scales. A streamor river, for example, has an inputoutput relationship

484 Water Resources Systems Planning and Management

with the next higher scale, the stream or river corridor.This corridor scale, in turn, interacts with the landscapescale, and so on up the hierarchy. Similarly, becauseeach larger-scale system contains the smaller scale ones,the structure and functions of the smaller systems affectthe structure and functions of the larger.

Investigating relationships between structure and scaleis a key first step for planning and designing stream orriver system management plans. Landscape ecologists usefour basic terms to define spatial structure at a particularscale.

These spatial landscape, component types in riverbasins, illustrated in Figure A.3 are:

Matrix. The dominant and interconnected land coverin the basin.

Patch. A different type of land cover found on smallerareas within the matrix.

Corridor. A land cover type that links other patches inthe matrix. Typically, a corridor is elongated in shape,such as a stream or river.

Mosaic. A collection of isolated patches.

The watershed scale that includes the stream corridor isa common scale of management, since many functions ofthe stream corridor are closely tied to drainage patterns.

While the watershed scale is often the focus of riverrestoration and water resources management, especiallyfor non-point pollutant discharge management, the otherspatial scales should also be considered when developinga stream or river system management policy or plan. The

E020801h

functional characteristics

flux of matter

retention

structural characteristics

species diversity

gradients and

zonations in species

hydrology

geomorphology

water quality

abiotic system

biotic systemriver system

land use emissions

river regulation

dams, levees

waste water discharges

human system

Figure A.1. Cause and effect

chain of factors influencing a

river system.



6/78


exclusive use of watersheds for the large-scale manage-

ment of stream corridors, however, ignores the materials,energy and organisms that move across and throughlandscapes independent of water drainage. A morecomplete large-scale perspective of the stream andriver system management is achieved when watershedhydrology is combined with landscape ecology and whenactions in problem sheds rather than only in drainagebasins are being considered.

2.1.1. Stream Channel Structure Equilibrium

Nearly all channels are formed, maintained and alteredflows and sediment loads. Channel equilibrium invothe relation among four basic factors: sediment dischaQs; sediment particle size, D; streamflow, Qw; and streslope, S. Lane (1955), using median particle size,expressed this relationship qualitatively as:

Qs D50 Qw S (A

reach scale

stream corridor scalestream scale

landscape scaleregion scale

watershed

local region

river watershed

mixed landscapesuburban

agricultural

forest cover

stream corridor

reservoir

watershed

reach

E020801j

Figure A.2. River basin compone

viewed at multiple spatial scales,

from the large regional scale to thlocal stream segment scale.



7/78

This relationship states that a measure of sediment load(sediment discharge Qs times median particle size D

50

) isproportional to a measure of the streamflow power(streamflow Qw times slope S). Channel equilibriumoccurs when the streamflow power is constant over thelength of the stream. If this occurs, no net changes inthe channel shape will occur. If a change occurs in eitherthe left or right-hand side of Equation A.1, the balance andhence equilibrium will be temporarily lost. If one variablechanges, one or more of the other variables must changeappropriately if equilibrium is to be maintained. Reachingequilibrium typically involves erosion and/or deposition.

Assuming increasing flows from runoff in the down-stream direction, the channel slope has to be decreasingin the downstream direction. If the slope is too steep,sediment is deposited to reduce that steepness. This iswhy stream channels that experience increasing down-stream flows have decreasing slopes in the downstreamdirection.

If streams in equilibrium have constant streamflowpower, QwS, over distance, from Equation A.1, thesediment load, QsD50, must also be constant. Hence,if sediment deposition is occurring in the downstream

direction to decrease stream slopes, the median particlesize, D50, will be decreasing and the sediment discharge,Qs, along with streamflow, Qw, will be increasing. Thisis typically observed in channels with increasingdownstream streamflows.

A stream seeking a new equilibrium tends to erodemore sediment and larger particle sizes. Alluvial streamsthat are free to adjust to changes in these four variables


generally do so and re-establish new equilibrium condi-tions. Non-alluvial streams such as those flowing overbedrock or in artificial, concrete channels are unable tomaintain this equilibrium relationship because of theirinability to pick up additional sediment.

The stream balance expressed in Equation A.1 can be

used to make qualitative predictions about the impactsof changes in runoff or sediment loads from a watershed.Quantitative predictions, however, require the use ofmore complex simulation or physical models.

2.1.2. Lateral Structure of Stream or River Corridors

Stream and river valleys are created over time by the streamor river depositing sediment as it moves back and forthacross the valley floor. These processes of lateral migrationand sediment deposition, usually occurring during floodflows, continually modify the floodplain. Through time, asthe channel migrates, it will maintain the same average sizeand shape as long as the channel stays in equilibrium.

One can distinguish two types of floodplains. Thehydrological floodplain is the land adjacent to the base-flow channel residing below bank-full elevation. It isinundated about two years out of three. Not every streamcorridor has a hydrological floodplain. The topographicfloodplain is the land adjacent to the channel, includingthe hydrological floodplain, that is flooded by a flood

peak of a given frequency (for example, the 100-yearflood the flood that is equalled or exceeded once every100 years on average defines the 100-year floodplain).Higher flood-peak flow return periods define widertopographic floodplains. These two types of floodplainsare shown in Figure A.4.

bankfull

elevation

topographic floodplain

hydrological floodplain

E020801m

Figure A.4. Two types of floodplains, the hydrological and

topographic.

Figure A.3. River basin landscapes made up of matrix, patch,

corridor and mosaic components at various scales.

E020801k

matrix

patch patch

matrix

matrixmosiac

patch

patchpatch



8/78


Floodplains provide temporary storage space forfloodwaters and sediment. This lengthens the lag timeof a flood. This lag time is the time between the middle ofthe rainfall event and the runoff peak. If a streamscapacity for moving water and sediment is diminished, orif the sediment loads become too great for the stream to

transport, the valley floor will begin to fill.Topographic features on the floodplain, as illustrated

in Figure A.5, include:

Meander scroll. A sediment formation marking formerchannel locations.

Chute. A new channel formed across the base of ameander. As it grows in size, it carries more of the flow.

Oxbow. A severed meander after a chute is formed. Clay plug. A soil deposit at the intersection of an

oxbow and the new main channel.

Oxbow lake. A water body created after clay plugsseparate the oxbow from the main channel. Natural levees. Formations built up along the bank

of some streams that flood. As sediment-laden waterspills over the bank, the sudden loss of depth andvelocity causes coarser-sized sediment to drop out ofsuspension and collect along the edge of the stream.

Splays. Delta-shaped deposits of coarser sedimentsthat occur when a natural levee is breached. Naturallevees and splays can prevent floodwaters from return-ing to the channel when floodwaters recede.

Backswamps. A term used to describe floodplainwetlands formed by natural levees.

These different features provide a variety of habitatsplants and animals.

2.1.3. Longitudinal Structure of Stream or River

Corridors

The processes that determine the characteristic latstructure of a stream corridor also influence its longitunal structure. For streams and rivers whose flows incrwith distance downstream, channel width and dealso increase downstream due to increasing drainage aand discharge. Even among different types of streamcommon sequence of structural changes, as shownFigure A.6, is observable from headwaters to mouth.

The longitudinal profile of many streams can be diviinto three zones. The changes in the three zones

characterized in Figure A.6. Zone 1, the headwater zohas the steepest slopes. In this zone sediments erode fslopes of the watershed and move downstream. The riin hilly regions are characterized by the swiftness of flow in restricted and/or steep channels, the occurrenclandslides and the formation of rapids along their courThe control of rivers in the upper reaches is knowntorrent control. Zone 2, the transfer zone, receives somthese sediments and hence is usually characterizedwider floodplains and more meandering channel patteThe flatter slopes in zone 3 receive most of the coarser s

iments. River training methods are often adopted managing alluvial rivers in this most downstream zone

A

C

B

D

F

E

E

GH

F splay-

G

H

backswamp

natural levee

-

-

A oxbow lake-

B chute-

E meander

scrolls

-

C clay plug-

D oxbow-

E020801n

Figure A.5. Topographic

features of a meandering

stream on a floodplain.



9/78

Though Figure A.6 displays headwaters as mountainstreams, these general patterns and changes apply towatersheds with relatively small topographic relief fromthe headwaters to the mouth. Erosion and depositionoccur in all zones, but the zone concept focuses on themost dominant process.

2.2. Drainage PatternsOne distinctive aspect of a watershed or river basin whenobserved from above (birds-eye view) is its drainagepattern. Drainage patterns are primarily controlled bytopography and geologic structure. Figure A.7 shows amethod of classifying, or ordering, the hierarchy of naturalchannels within a watershed or basin. This is a modifiedmethod based on the one proposed by Horton (1945).


The uppermost channels in a drainage network (head-water channels with no upstream tributaries) are desig-nated as first-order streams down to their first confluence.

A second-order stream is formed below the confluence oftwo first-order channels. Third-order streams are createdwhen two second-order channels join, and so on. Theintersection of a channel with another channel of lowerorder does not raise the order of the stream below the

intersection, e.g. a fourth-order stream intersecting with,a second-order stream is still a fourth-order stream belowthe intersection.

Within a given drainage basin, stream order correlateswell with other basin parameters, such as drainage area orchannel length. Consequently, knowing what order a streamis can provide clues to other characteristics, such as itslongitudinal zone and its relative channel size and depth.

(~downstream distance

drainage area2)

increase

headwater transfer deposition

bed

m

aterialgrain

size

slop

e

char

acte

ristic

stre

amdis

charg

e

channel width

channel depth

mean flow velocity

re

lativ

evolum

e

of s

tored

alluv

ium

E0204

22

e

zone1

zone2

zone3

Figure A.6. Typical changes in the

stream channel characteristics

along its length.



10/78


2.2.1. Sinuosity

Sinuosity (Figure A.8) is a term indicating the amount ofcurvature in the channel. The sinuosity of a reach is itschannel centreline length divided by the length of thevalley centreline. If the channel-length/valley-length ratiois more than about 1.4, the stream can be considered

meandering in form. Sinuosity is generally related tostreamflow power (slope times flow). Low to moderatelevels of sinuosity are typically found in zones 1 and 2 ofthe longitudinal profile (Figure A.6). Sinuous streamsoften occur in the broad, flat valleys of zone 3.

2.2.2. Pools and Riffles

Most streams share a similar attribute of alternating, regu-larly spaced, deep and shallow areas calledpools and riffles(Figure A.8). Pools and riffles are associated with the

deepest path along the channel (thalweg). This deepestpath meanders within the channel. Pools typically form inthe thalweg near the outside bank of bends. Riffle areasusually form between two bends at the point where thethalweg crosses over from one side of the channel tothe other. The pool-to-pool or riffle-to-riffle spacing, wherethey exist, is normally about five to seven times the chan-nel width at bank-full discharge (Leopold et al., 1964).

2.3. Vegetation in the Stream and RiverCorridors

Vegetation typically varies along and across stream river corridors. In zone 1, flood-dependent or tolerplant communities tend to be limited but provide veative organic matter along with the sediment to zoneand 3 downstream. Woody debris from headwaforests can be among the important features supporfood chains and instream ecological habitats in riv

(Maser and Sedell, 1994).Zone 2 is typically a wider and more complex floodp

and larger channel than zone 1. The lower gradient, lastream size and less steep terrain in zone 2 often allow magricultural or residential development. This developmmay restrict the diversity of the natural plant communiin the middle and lower reaches, especially when land uinvolve clearing and narrowing the corridor. Such actialter stream processes involving flooding, erosion/deption, and import or export of organic matter and sedimThis affects stream corridor geomorphology, hab

diversity, and water quantity and quality regimes.The lower gradient, increased sediment deposit

broader floodplains and greater water volume in zontypically lead to different plant communities than thfound in the upstream zones. Large floodplain wetlacan develop on the flatter terrain.

The changing sequence of plant communities alstreams from source to mouth is an important sourc

1

2

31

11

1

1

1 1

1

1

11

1

1111

2

2

2

3

3

4

E020801o

4

2

2

4

Figure A.7. Stream ordering in a drainage network showingfirst-order streams down to fourth-order streams.

sinuous

straight

pool

thalweg line

riffle or cross over

Figure A.8. Sequence of pools and riffles in straight and

sinuous streams.



11/78

ecosystem resiliency. A continuous corridor of nativeplant communities is desirable. Restoring vegetativeconnectivity in even a portion of a stream will usuallyimprove conditions and enhance the ecosystems beneficialfunctions.

2.4. The River Continuum Concept

The river continuum concept identifies biological connec-tions between the watershed, floodplain and perennialstream systems, and offers an explanation of how biolog-ical communities develop and change along perennialstream or river corridors. The concept is only a hypo-thesis, yet it has served as a useful conceptual model fordescribing some of the important features of perennialstreams and rivers.

The river continuum concept assumes that, because offorest shading in many first to third-order headwaterstreams, the growth of algae, periphyton and otheraquatic plants is limited. Since energy cannot be createdthrough photosynthesis (autotrophic production),aquatic organisms in these lower order streams dependon materials coming from outside the channel such asleaves and twigs. Consequently, these headwater streamsare considered heterotrophic (that is, dependent onthe energy produced in the surrounding watershed). Therelatively constant temperature regimes of these streams

tend to limit biological species diversity.Proceeding downstream to fourth, fifth and sixth-

order streams, the channel widens, which increases theamount of incident sunlight and average temperatures.Primary production increases as a response. This shiftsmany stream organisms to internal autotrophic produc-tion and a dependence on materials coming from insidethe channel (Minshall et al., 1985). Species richness of theinvertebrate community increases due to the increase inthe variety of habitats and food resources. Invertebratefunctional groups, such as the grazers and collectors,

increase as they adapt to both out-of-channel and in-channel sources of food.

Mid-ordered streams also experience increasingtemperature fluctuations. This tends to further increasebiotic diversity. Larger streams and rivers of seventh totwelfth order tend to increase in physical stability, butundergo significant changes in structure and biologicalfunction. Larger streams develop increased reliance on


primary productivity by phytoplankton, but continue toreceive heavy inputs of dissolved and fine organic parti-cles from upstream.

Large streams frequently carry increased loads ofclays and fine silts. These materials increase turbidity,decrease light penetration, and thus increase the signifi-

cance of heterotrophic processes. The frequency andmagnitude of temperature changes decrease as stream-flows increase, and this in turn increases the overallphysical stability of the stream as well as species compe-tition and predation.

2.5. Ecological Impacts of Flow

Streamflow regimes have a major influence on the physi-cal and biological processes that determine the structureand dynamics of stream ecosystems (Covich, 1993). Highflows are important in terms of sediment transport. Theyalso serve to reconnect floodplain wetlands to thechannel. Floodplain wetlands provide habitat for aquaticplants as well as fish and waterfowl. Low flows promotefauna dispersment, thus spreading populations of speciesto a variety of locations. The life cycles of many riverinespecies require an array of different habitat types, whosetemporal availability is determined by the variable flowregime. Adaptation to this environment allows riverinespecies to persist during periods of droughts and floods

(Poff et al., 1997).

2.6. Geomorphology

The major large-scale physical characteristics of moststreams and rivers have resulted from hydro-geologicalprocesses that have occurred over periods ranging fromseveral decades to hundreds or even thousands of years. Atsmaller spatial scales, interactions between the hydrologicalcycle and the land that can alter the geometry of these waterbodies take place in much shorter times, possibly ranging

from a few minutes, hours or days to several years. Land usechanges also influence the shape and flow directions ofstreams, rivers, estuaries and coastlines. Understanding howthis happens requires a knowledge of how land cover andland-cover changes influence the partitioning of precipita-tion into runoff, infiltration, soil water storage, groundwaterflow and storage, and discharge, and what impact all thishas on the erosion, transport and deposition of sediment.



12/78


2.6.1. Channel Classification

Streams and rivers are classified on the basis of theirdimensions, configurations and shapes. Classifying chan-nel morphology helps in the development of reproducibledescriptions and assessments of channel flows, movementand sediment transport potential. Rosgen (1996) classi-fied stream or river morphology based on bank-fullwidth, channel sinuosity, slope and channel material size.

While classifying a stream or river channel is helpful inunderstanding the behaviour of the channel and howthe behaviour might change due to land use changesor modifications to the channel, it is only an aid in the

management of a stream or river or in the development ofan engineering design for its channel. Classification itselfdoes not directly provide the detailed information neededfor an engineering design solution.

The ratio of the flood-prone area width to thebank-full width is called the entrenchment ratio. Thewidth-to-depth ratio is the ratio of the bank-full width tothe mean bank-full depth. The mean hydraulic depth is thecross-sectional area (darker blue area marked as depth inFigure A.9) divided by the wetted perimeter.

2.6.2. Channel Sediment Transport and Deposition

The energy contained in flowing water is typicallyexpended by eroding and transporting sediment. Thesource of sediment comes in the runoff from the drainagearea or from the channel bed and banks (Trimble andCrosson, 2000). The sediment transported in water canbe dissolved, suspended and pushed along the bed by

saltation and traction. The latter two processes formbedload. Figure A.10 illustrates these types of sedimloads in a river channel.

Sediments range from clays to gravel and, in extreevents, even boulders. They include clay (0.004 msilt (0.0040.062 mm), sand (0.0621.000 mm), gr(granules and pebbles, 164 mm), cobbles (64250 m

and boulders (250 mm). Each of these size classes be subdivided from fine to coarse. In addition, sediments can be cohesive (tending to attach to osediments) or non-cohesive.

Energy is required to erode and transport sedimThe heavier the sediment particles, the more enerequired to erode and transport them. The energy avable to do this is a function of the rate of flow. Figure A

E020916a

channel bankfull width

depth

bank bank

flood-prone area width

wetted perimeter

Figure A.9. Channel cross-sectio

schematic.

flow direction

dissolved

load

suspended

load

saltation

tra cti on

river bed

bed lo

Figure A.10. Types of sediment loads in a river channel.



13/78

shows the approximate flow rates, in centimetres persecond, needed to transport sediment particles of varioussizes. Note that the ability to erode and transport cohesivefine sediments is much less than non-cohesive sediments.

If the energy of flowing water exceeds that needed tocarry the existing sediment load, additional erosion canoccur to add to the sediment load. Flowing water will

seek to achieve its equilibrium sediment load. Converselyif the energy is insufficient to carry the existing load in thewater, some of it will be deposited.

Considerable efforts have been made over the pastdecades to estimate, prevent and control soil erosion andsediment runoff from watersheds. To the extent that theseprevention and control efforts have worked, increasedstream channel and bank erosion have occurred.Controlling watershed erosion does not reduce the sedi-ment carrying capacity of flows. If sediment is available inor on the banks of the stream or river channel, it will

replace what otherwise might have come from watershedrunoff. Especially in urbanizing watersheds, where water-shed contributions to sediment loads have been substan-tially reduced, most of the total sediment yield can be dueto channel and bank erosion.

Sediment is transported as bedload and/or as suspendedload. The latter consists of fine materials such as clay, siltand fine sand that usually make the flow look muddy. Flowsfrom snow or ice melt tend to carry fine particles of rock that


can make the flow look emerald green. Lake Louise inAlberta, Canada is a classic example of this. If fine materialsare available, the suspended load can be as high as 95% ofthe total sediment load carried by the stream or river flow.This fine material settles in areas of reduced velocity.Sediment deposition processes can eventually change thechannel dimensions and even its location.

Bedload transport of coarser sediments involves acombination of sliding, rolling and saltation (bouncing).These transport processes begin when the flow velocityreaches a critical value for the particular size of the bedmaterial. This critical velocity corresponds to a criticalshear stress. The shear stress associated with a flow is animportant parameter for sediment transport.

Suspended sediment particle settling (or fall) velocitiesinfluence the rate of deposition. These velocities areaffected by particle shapes, the density or specific weight ofthe sediment particles relative to that of the water, and the

chemical attraction (cohesion) of the particles, especially inclays. Equations have been proposed for estimating the ter-minal fall velocity of a single particle in quiescent, distilledwater. While equations and graphs exist in handbooks forthese and other individual particle size fall velocities underquiescent distilled conditions, measurements of fall veloci-ties under natural conditions are much more reliable.

Erosion depends on tractive stress or shear stress thatcreates lift and drag forces at the soil surface boundaries in

velocity(cm/s)

grain size (mm)

1000800500

200

100

50

20

10

5

2

10.001 0.005 0.02 0.05 0.1 0 .2 0.5 1 2 10 20 50 1005

clay silt

fine

sand

medium

to coarse

sand granules pebb les

cohesive

clayandsilt

non-cohesive fine clay and si lt

erosion of partic les from bed

tran

sitio

nzone

sedimentation of partic les onto bed

cobbles and boulders

E030526b

Figure A.11. Relation between

flow rate and sediment particle

size erosion and transport.



14/78


fields and along the bed and banks. Shear stress varies asa function of flow depth and slope. The larger the soilparticle, the greater the amount of shear stress needed todislodge and transport it downstream. The energy differ-ential that sets sediment particles into motion is created byfaster water flowing in the main body of the channel next

to slower water flowing at the boundaries. The momentumof the faster water is transmitted to the slower boundarywater. The resulting shear stress moves bed particles in arolling motion in the direction of the current.

Sediment transport rates can be computed usingvarious models, but the uncertainty associated with anysediment load prediction can be considerable. Predictingsediment transport is one of the most enduring challengesfacing hydrologists and geomorphologists.

Stream channels and their floodplains are constantlyadjusting to the water and sediment in them. Channelresponse to changes in water and sediment yield mayoccur at differing times and locations, requiring differinglevels of energy. Daily changes in streamflow and sedimentload result in frequent adjustment of bedforms and rough-ness in many streams with movable beds. Streams alsoadjust periodically to extreme high and low-flow events.Both flood and drought flows often remove vegetation aswell as creating and increasing vegetative potential alongstream and river corridors. Long-term adjustments inchannel structure and vegetation may come from changes

in runoff or sediment yield from natural causes, such asclimate change or wildfire, or from human activities suchas cultivation, overgrazing or rural-to-urban conversions.Changes in vegetation can also affect streamflow andsediment deposition. Bio-geomorphology is the term usedfor the study of these plant, soil and water interactions.

2.6.3. Channel Geometry

Like all physical systems, stream and river flows and theirsediment loads will attempt to reach an equilibrium. The

equilibrium between flows and sediment erosion, uptakeand deposition, is sometimes referred to as regime theory.Leopold and Maddock (1953) derived regime relations instream and river channels in alluvial (sedimentary) basins.These relations predicted the stream width, w; meanhydraulic depth, h; velocity, U; sediment concentration,Qs; slope, S; and Mannings n friction coefficient as apower function of the discharge, Q, in the stream or river.Each of these relations i is of the form aiQ

bi. Leopold and

Maddock found the values of these different coefficienand bi for a variety of rivers in the United States (alsRichardson et al., 1990).

The values of the coefficients ai and bi may differ althe length of the stream or river (Leopold, 1994). In downstream direction the relative change in the w

will increase more rapidly than the relative changevelocity. Hence, the coefficients ai and bi associated wwidth, depth and velocity will change. However, sinceproduct of width, depth and velocity equals the flowand each equation aiQ

bi for width, depth and velocityfunctions of the flow Q, both the product of the thcoefficients ai and the sum of the three exponent cocients bi must equal 1.

Other studies have found approximate relationshbetween bank-full channel dimensions of alluvial streand rivers and their bank-full discharge. The chandimensions, pattern and profile are primarily relatedthe effective or bank-full discharge. The magnitude ofbank-full discharge in the main channel typically cosponds to the 1.5- to 2-year expected return period fevent based on annual peak flows. The bank-full staglower than the top of the bank. It is commonly identifiea bench, a change in bank material and vegetation, ortop of a point bar (Rosgen, 1996; Ward and Elliot, 199

The loglog plot of Figure A.12 shows a relationsbetween flow rates and depths in relation to bank-

flow rates and depths for thirteen rivers in the easUnited States (Leopold et al., 1992).

The dimensionless rating curve presented in Figure Ashows that the annual discharge is less than the bank

flow Q / bankfull QB

depth

D

/bankfulldepth

DB 8.00

4.00

2.00

1.00

0.50

0.25

0.125

0.1 101.0

mean annual Q

bankfull depth

bankfull flow

1.5 5 10 25 50 100

return period (years)

E020226m

Figure A.12. Dimensionless regression curve based on

thirteen gauging stations in the eastern United States

(Leopold, Wolman and Miller, 1992).



15/78

discharge and occurs at a stage of about a third of thebank-full depth. A 50- to 100-year return period dischargeoccurs at a stage that is about double the maximum bank-full depth. In developing a stream classification system,Rosgen (1996) defined a flood prone width as one thatoccurs at twice the maximum bank-full depth. Therefore, itmight be expected that this depth corresponds to about the100-year return period discharge.

2.6.4. Channel Cross Sections and Flow Velocities

Typically, flow velocity across a channel will vary from onebank to another. This lateral variation will change along astream or river channel. For example, the velocity near theouter bank of a meander will be higher than near the innerbank because water near the outer bank has to travelfurther. Also, the velocity decreases towards the bottom orsides of the channel due to the surface roughness of thechannel. Water in contact with the bottom and sides will be

stationary. These relationships are shown in Figure A.13.The velocity distribution in a channel can change from

one cross section to the next. Typically, at any cross sec-tion in a channel, there will be a portion of the flow abovethe deepest point (the thalweg) that is moving the fastest.

Along the thalweg the velocity increases in riffles,decreases in pools, moves from side to side, up and downwith depth, and rotates as it moves around bends. The


rotation of the flow on the outer bend might also createundercut concave banks.

The velocity decreases near the bottom or sides ofthe channel due to the roughness of its surface. Water incontact with the bottom and sides will be stationary. Thechanging velocities from riffles to pools will cause turbu-lence. Also, as water moves through pools, it will pushtowards the banks and away from its direction of flow. Asmuch as a third of the flow might circulate back

upstream.The bank-full discharge is most effective in forming a

channel, benches (active floodplains), banks and bars. Itis this discharge rate that, as shown in Figure A.14,transports the largest total sediment load over time. Thesediment concentration in the water is a function of theflow discharge rate and of course the available sediment.Low discharge rates are ineffective in transportingsediment, while high ones have very high sedimenttransport rates. However, extremely high discharge eventsoccur less frequently, so the total sediment load they carry

over a period of many years is not the largest.A measure of the total sediment load carried by a

particular discharge equals the event frequency multi-plied by the transport rate for that discharge. The maxi-mum value of that product for all discharges is called theeffective discharge. This effective discharge is the bank-fulldischarge. It has the longest-term impact on an alluvialstreams or rivers equilibrium morphology.

relative channel flow velocities

straight channel

3.0

2.5

2.0

1.5

1.0

0.5

0.0

average channel bend

E020226

d

Figure A.13. Typical channel relative velocities at bank-full

flows. The velocities at the outside of channel bends (the

right-hand side of the lower channel) are greater than on theinside of the bends.

E020226

e

sediment transport rate

frequency of occurrence

effective sediment discharge

maximum effective discharge

stream or river flow

bankfull discharge

Figure A.14. The bank-full discharge typically has the largest

total sediment load.



16/78


Discharges larger than the mean annual dischargetypically transport more than 95% of the sediment in ariver system.

2.6.5. Channel Bed Forms

Bed forms result from the interaction of the fluid forcesand sediment particles. Bed forms in alluvial streams andrivers also depend on channel shape, size of bed material,bed vegetation and the viscosity of the fluid. In flumeshaving a limited range in depth and discharge, changingthe slope is the principal means of changing the bed forms.In streams and rivers, however, where the slope isrelatively constant, a change in bed form can occur with achange in discharge and/or a change in viscosity. Viscosityis affected by a change in sediment size distribution and/ortemperature. An increase in viscosity resulting from adecrease in temperature or an increase in fine sedimentssuch as clays can change a dune bed to washed-out dunes,plane beds or antidunes. For example, the Missouri River

in the United States along the border between Iowa Nebraska has temperatures between 21 and 27 C insummer and between 15 and 17 C in the autumnsummer, its bed form is characterized by dunes. In autuits bed form becomes washed-out dunes (USACE, 196

2.6.6. Channel Planforms

Channel planforms are what one sees when lookinthem from above. Their geographic shapes canbroadly grouped into straight, meandering and braiplanforms (Lagasse et al., 1991; Leopold and Wolm1957; Schumm, 1972, 1977; Richardson et al., 199These three types of channels are shown in Fig

A.15. More detai led classifications have been u(Brice and Blodgett, 1978; Culbertson et al., 1967), these three basic types are the ones most commoconsidered.

A meandering stream is characterized by sinuS-shaped flow patterns. The sinuosity of a channel of fi

meanderingstraightbraided

point bar

crossing

aa

b cb c

d d

ee

f

f

a a

b b

c c

d d

e

f

e

f

E021029n

Figure A.15. Types of chann

planforms (after Richardsonet al., 1990).



17/78

length is the ratio between its length and the straight-linedistance between channel end points, or valley length.Channels can be classified according to their sinuosity. Ifthe sinuosity is 1.0 the channel is called straight, a condi-tion that rarely occurs in natural alluvial channels exceptover short distances. If the sinuosity is greater than 1.0 thechannel is called sinuous. If the sinuosity is greater thanabout 1.4 the river is said to meander, and if the sinuosityexceeds 2.1 the degree of meandering is tortuous.

Figure A.16 defines some geometric parameters ofmeandering channels.

A braided stream or channel consists of a number ofsubordinate channels. At normal and low flow rates,

these subordinate channels are separated by bars, sand-bars or islands. The shape and location of the bars andislands can change with time, sometimes with each runoffevent. In an anabraided stream or river, the subordinatechannels are more permanent and more widely and dis-tinctly separated than those of a braided stream.

A stream or river channel can have different planforms atdifferent locations along its length. Channel planforms canaffect channel dimensions, flows, bed material, floodplainsize and plant cover. Channel planforms in turn are affectedby geology, topography, the drainage area of the contribut-

ing watershed, flow velocity, discharge, sediment transport,sediment particle distribution, channel geometry, vegetationcover and any geomorphologic controls on the system.

2.6.7. Anthropogenic Factors

Stream and river morphology is affected by humanactivities such as changing land use, bank protection,navigation, and construction and operation of hydraulic


infrastructure. Deforestation and cultivation of watershedareas, water management initiatives and floodplain devel-opment affect the runoff and the sediment yield to theriver; they also influence the hydraulic roughness andthe trapping of sediment during floods.

Urbanization increases the fraction of impervious land

in a drainage area. This in turn reduces infiltration andcauses more runoff and higher peak discharges.Sediment loads typically increase during constructionand decrease following construction. All of these factorsaffect the equilibrium in the river and can cause it towiden and/or deepen. Channel modifications such asstraightening a reach of the channel will also increasethe sediment-carrying capacity of the discharge andmight cause bank and bed scour.

Urbanization increases the frequency as well as theamounts of water associated with different runoff events

(Figure A.17). Increasing imperviousness increases thenumber of expected runoff events each year. The soilmoisture that exists at the beginning of a storm also influ-ences the frequency of runoff events. In areas of Ohioin the United States, Ward (personal communication)found at the start of a storm event in a rural area withwet soil conditions there might be only one 1-cm runoffevent annually and a 2-cm runoff event every few years.However, a low-density urban area or an urban area with

wavelength

beltwidth

amplituderadius

of curvature

bend length =

0.5 wavelength

E020226

g

Figure A.16. Geometry of a meandering stream (Rosgen,

1996).

expected

eventsperyear

runoff

E020226a

urban

urban

rural

(high, wet)

(low, dry)

(wet)

Figure A.17. Expected annual occurrences of runoff

events showing the effect of high and low urban and rural

development densities under wet and dry soil moistureconditions at the beginning of a storm (Ward, personal

communication).



18/78


dry soil conditions at the start of a storm event might onaverage experience six or seven 1-cm runoff events, twoor three 2-cm events, one 2.5-cm event per year, and evenan event with 3.5-cm every few years. High-density urbanareas, or urban areas with wet soil conditions at the startof a storm event will on average experience more than

twenty 1-cm runoff events, six 2-cm events, two 2.5-cmevents, and one 3.5-cm event per year. These were forthis study area in Ohio; for other areas elsewhere thenumbers will differ, but the general relationships shownin Figure A.17 will apply.

The effect of urbanization on discharges is alsoillustrated in Figures A.18 and A.19. Rural areas will havelittle if any impervious cover, while urban areas will haveconsiderably more. The plot shows the relative discharge(percentage of the rural discharge) increase that occurs asthe percentage of impervious cover increases. Plots arepresented for flow return periods of 2, 10 and 100 years.Note that the biggest impact is on the smaller, morefrequent storm events. The two-year return perioddischarges, Q2, in highly urbanized areas can be over two-and-a-half times larger than those on rural areas. In addi-tion, as imperviousness increases, so does channel width.

2.7. Water Quality

Establishing an appropriate flow regime in a stream or

river corridor may do little to ensure a healthy ecosystemif the physical and chemical characteristics of the waterare damaging to that ecosystem. For example, streams orrivers with high concentrations of toxic materials, hightemperatures, low dissolved oxygen concentrations orother harmful physical/chemical characteristics cannotsupport healthy stream corridor ecosystems.

Figure A.20 illustrates some of the key water qualityprocesses affecting the oxygen content and hence the biologyof surface waters. (The modelling of these and other chemi-cal and biological processes is discussed in Chapter 12.)

Dissolved oxygen (DO) is a basic requirement for ahealthy aquatic ecosystem. Most fish and aquatic insectsbreathe the oxygen dissolved in the water body. Somefish and aquatic organisms, such as carp and sludgeworms, are adapted to low oxygen conditions, but mostsport-fish species, such as trout and salmon, suffer whenDO concentrations fall below a concentration of 34 mg/l.Larvae and juvenile fish are more sensitive and requireeven higher concentrations of DO.

Many fish and other aquatic organisms can recofrom short periods of low oxygen concentrationsthe water. However, prolonged episodes of depres

dissolved oxygen concentrations of 2 mg/l or less result in dead (anaerobic) water bodies. Prolonexposure to low DO conditions can suffocate adult or reduce their reproductive survival rate by suffocasensitive eggs and larvae, or starve fish by killing aquinsect larvae and other sources of food. Low concentrations also favour anaerobic bacteria produce the noxious gases often associated with polluwater bodies.

discharge

increase(%)

relative imperviousness

E020226b

Q

QQ

2

0

00

1

1

Figure A.18. Relative discharge increases, for flows havin

10- and 100- year return periods, as a function of degree o

impervious surface area.

channel width increase (%)

relative imperviousness

E020226c

100

80

60

40

20

0

Figure A.19. Relative increase in channel width as a funct

of impervious surface area.



19/78

Water absorbs oxygen directly from the atmosphere,and from plants as a result of photosynthesis. The amountof oxygen that can be dissolved in water is influenced byits temperature and salinity. Water loses oxygen primarilyby respiration of aquatic plants and animals, and by themineralization of organic matter by microorganisms.Discharges of oxygen-demanding wastes or excessiveplant growth (eutrophication) induced by nutrient load-ing followed by death and decomposition of vegetative

material can also deplete oxygen.In addition to oxygen and water, aquatic plants require a

variety of other elements to support their bodily structuresand metabolism. Just as with terrestrial plants, nitrogenand phosphorus are important among these elements.

Additional nutrients, such as potassium, iron, selenium andsilica, are also needed by many species but are generally notlimiting factors to plant growth. When any of these elements


are limited, plant growth may be limited. This is an impor-tant consideration in ecosystem management.

Nutrients cycle from one form to another dependingon nutrient inputs, as well as temperature and availableoxygen. The nitrogen cycle is illustrated in Figure A.21 asan example. Table A.1 lists some common sources ofnitrogen and phosphorus nutrient inputs and their typicalconcentration ranges.

Management activities can interact in a variety of

complex ways with water quality. This in turn can affectecosystem species, as shown in Figure A.22.

2.8. Aquatic Vegetation and Fauna

Stream biota are often classified in seven groups: bacteria,algae, macrophytes (higher plants), protists (amoebas,flagellates, ciliates), microinvertebrates (such as rotifers,

E020801q

algae

photosynthesis respiration

reaeration

carbonaceous

deoxygenation

oxygen

demand

NH+4

NO

NO

-

-

2

3

dissolved

oxygen

nitrification

Figure A.20. Some of the basic

chemical and biological

processes affecting dissolvedoxygen in waters.



20/78


litter input

dissolved organic

nitrogenNH

NO3

3

biota

cyanobacteriaand microbial

populations

benthic algae

particulate

organic

matter

and

associated

microbes

NH 3

N2

NH 3

O

NO3

nitrogen

fixation

nitrogen

fixation

NO2

NH 3excretion

decomposition

NH 3 accumulation

decomposition

/excretion

NH

NO3

3

dissolved

organic

nitrogen

assimilation

N 2

assimilation NO3

nitrificat

ion

denitrification o

xygen

concentration

riparian

vegetation

N 2

import from

upstream

atmospheric N 2

sediment

surface

inter-

stitial

water

groundwater dissolved organic nitrogen NO3

E020801r

downstreamexport to

Figure A.21. Dynamics and

transformations of nitrogen

stream ecosystem.

urban runoff

livestock operations

atmosphere

90 % forest50 % forest

90 % agriculture

untreated waste water

treated waste water

(wet deposition)

source total

nitrogen (mg/l)

total

phosphorus (mg/l)

3-10

6-800

0.9

0.06-0.190.18-0.34

0.77-5.04

35

30

0.2-1.7

4-5

0.015

0.006-0.0120.013-0.015

0.085-0.104

10

10

E020903e Table A.1. Sources and concentrations of

pollutants from common point and non-po

sources (USDA, 1998). These data show lit

or no impact on nutrient removals from ba

wastewater treatment facilities.



21/78

copepods, ostracods, and nematodes), macroinvertebrates(such as mayflies, stoneflies, caddisflies, crayfish, worms,clams, and snails) and vertebrates (fish, amphibians,reptiles, and mammals). The river continuum concept

provides a framework for describing how these organismschange from lower to higher-order streams.

Much of the spatial and temporal variability of type,growth, survival and reproduction of aquatic organismsreflects variations in water quality, temperature, stream-flow and flow velocity, substrate content, the availabilityof food and nutrients, and predatorprey relationships.These factors are often interdependent.


2.9. Ecological Connectivity and Width

Healthy ecosystems also depend on conductivityand width. Connectivity is a measure of how spatially

continuous a corridor or a matrix is (Forman and Godron,1986). A stream corridor with connections among itsnatural communities promotes transport of materialsand energy and movement of flora and fauna.Connectivity is illustrated in Figure A.23.

Width is the distance across the stream and its zone ofadjacent vegetation cover. Factors affecting width areedges, community composition, environmental gradients

fine particulateorganic matter

dissolved

organic matter

invert

ebrate shre

dders inve

rtebrate scra

pers

inve

rtebrate predato

rsverte

brate predato

rs

inve

rtebrate collecto

rs

micro

organisms ep

ilithic algae

larger plants

mosses, red algae

coarse

partic

ulate organicm

atter

e.g. hyphomycete

fungi

flocculation micro organisms

E020801s

Figure A.22. Interactions

among aquatic organisms and

their sources of energy.(Dashed lines reflect weaker

interactions.)



22/78


and disturbance effects of adjacent ecosystems, includingthose due to human activity. Width and connectivity

interact throughout the length of a stream corridor.Corridor width varies along a stream and may have gaps.Gaps across the corridor can interrupt and reduceconnectivity. Ensuring connectivity and adequate widthcan provide some of the most useful ways to mitigatedisturbances.

2.10. Dynamic Equilibrium

In constantly changing ecosystems like stream and rivercorridors, the stability of a system is its ability to persist

within a range of conditions. Within this range the systemis resilient. This phenomenon is referred to as dynamicequilibrium.

The maintenance of dynamic equilibrium requires aseries of self-correcting mechanisms in the streamcorridor ecosystem. These mechanisms control theresponses to external stresses or disturbances withincertain ranges. The threshold levels associated with theseranges are often difficult to identify and quantify. If theyare exceeded, the system can become unstable. Corridorsmay then undergo a change toward a new steady-state

condition, usually after some time for readjustment hasoccurred.

Many stream systems can accommodate some distur-bances and still return to functional conditions once thesources of the disturbances are removed. Ecosystems tendto heal themselves when external stresses are removed.The time it takes to do this, of course, depends on thelevel of stress.

2.11. Restoring Degraded Aquatic Systems

Some principles found useful in the managementrestoration activities in degraded stream or river systare listed below. These principles apply from eplanning to post-implementation monitoring. They fo

on scientific and technical measures and their likimpacts. Restoration activities can include uplbest-management practices for agriculture, stream chanrestoration, removal of exotic species and increasing naplant cover, establishing windbreaks and shelterbimproving upland corridors and riparian habitat, wetland enhancement for water quality improvementsin all management activities, the presence or absencpublic support for a restoration project can make difference between success and failure.

Preserve and Protect Aquatic Resources

Existing ecosystems that are relatively intact providenatural materials needed for the recovery of impasystems. It is not usually necessary to import species.

Restore Ecological Integrity

Restoration should re-establish the ecological integritdegraded aquatic ecosystems. Ecological integrity re

to the natural structure, composition and processebiotic communities and the physical environment. processes, such as nutrient cycles, succession, wlevels and flow patterns, and the dynamics of sedimerosion and deposition, function within the natural raof variability. Restoration strives toward ecologintegrity by taking actions that favour the desired natuprocesses and communities that can be sustaithrough time.

Restore Natural Structure and FunctionMany aquatic resources in need of restoration hproblems caused by past changes in channel formother physical characteristics that led to problems suchabitat degradation, changes in flow regimes siltation. Stream channelization, ditching in wetlandisconnection from adjacent ecosystems and shoremodifications are examples of such adverse changes.

E020801t

Figure A.23. Landscapes with high (left picture) and low (right

picture) degrees of connectivity.



23/78

Structure and function are closely linked in rivercorridors, lakes, wetlands, estuaries and other aquaticresources. Re-establishing the appropriate natural struc-ture can bring back beneficial functions. For example,restoring the bottom elevation in a wetland can helpre-establish the hydrological regime, natural disturbance

cycles and nutrient fluxes. Monitoring the extent to whichdesired functions have been re-established can be a goodway to determine the effectiveness of a restoration project.

Work Within the Watershed and Broader Landscape

Context

Restoration requires a design based on the entire watershedor river basin, not just the part of it that is degraded. A local-ized restoration project may not be able to change what goeson in the whole watershed, but it can be designed to accom-modate watershed effects better. New and future urbandevelopment may, for example, increase runoff volumes,streambed down-cutting, bank erosion and pollutant load-ing. Restoration may help mitigate these adverse effects. Forexample, in choosing a site for a wetland, stream or riverrestoration project, planners should consider how theproposed project may be used to further related efforts inthe watershed, such as increasing riparian habitat continu-ity, reducing flooding and/or enhancing downstream waterquality. Beyond the watershed, the broader landscape

context also influences restoration through factors such asinteractions with terrestrial habitats in adjacent watersheds,or the deposition of airborne pollutants from other regions.

Understand the Natural Potential of the Watershed

A watershed has the capacity to become only what itsphysical and biological setting its climate, geology,hydrology and biological characteristics will support.Establishing restoration goals for a water body requiresknowledge of the natural range of conditions that existed

on the site prior to degradation and of what future condi-tions might be. This information can then be used indetermining appropriate goals for the restoration project.

Address Ongoing Causes of Degradation

Restoration efforts are likely to fail if the causes ofdegradation persist. Therefore, it is essential to identify thecauses of degradation and eliminate or mitigate them


wherever possible. Degradation can be caused by oneevent, such as the filling of a wetland, or it can be causedby the cumulative effect of numerous events, such asgradual increases in the amount of impervious surfaces inthe watershed that alter the streamflow regime. In identi-fying the sources of degradation, it is important to look at

upstream and upslope activities as well as at direct impactson the immediate site where damage is evident. In somesituations, it may also be necessary to consider down-stream modifications such as dams and channelization.

Develop Clear, Achievable and Measurable Goals

Goals direct implementation and provide the standardsfor measuring success. The chosen goals should beachievable given the natural potential of the area and theavailable resources and the extent of community supportfor restoration. Goals provide focus and increase projectefficiency. They can also change (adapt) over time.

Focus on Feasibility

Particularly in the planning stage, it is critical to focus onwhether any proposed restoration activity is feasible, takinginto account scientific, financial, social and other consider-ations. Community support for a project is needed to ensureits long-term viability. Ecological feasibility is also critical.

For example, a wetland, stream or river restoration projectis not likely to succeed if the hydrological regime thatexisted prior to degradation cannot be re-established.

Use a Reference Site

Reference sites are areas that are comparable in structureand function to the proposed restoration site before itwas degraded. They may be used to identify targets forrestoration projects, and as yardsticks for measuringthe progress of the project. While it is possible to use

historic information on sites that have been altered ordestroyed, it may be most useful to identify an existing,relatively healthy, similar site as a benchmark.

Anticipate Future Changes

Although it is impossible to plan for the future precisely,foreseeable ecological and societal changes can andshould be factored into restoration design. For example,



24/78


in repairing a stream channel, it is important to take intoaccount potential changes in runoff resulting fromprojected increases in upstream impervious surface areadue to development. In addition to potential impactsfrom changes in watershed land use, natural changes suchas plant community succession can also influence restora-

tion. Long-term, post-project monitoring should take intoaccount successional processes in a stream corridor whenevaluating the outcome of the restoration project.

Involve the Skills and Insights of a Multidisciplinary

Team

Restoration can be a complex undertaking that integratesa wide range of disciplines, including ecology, aquaticbiology, hydrology and hydraulics, geomorphology, engi-neering, planning, communications and social science.The planning and implementation of a restoration projectshould involve people with experience in the disciplinesneeded for that particular scheme. Complex restorationprojects require effective leadership to bring the variousdisciplines, viewpoints and styles together as an effectiveteam.

Design for Self-Sustainability

Perhaps the best way to ensure the long-term viability of

a restored area is to minimize the need for continuousoperation, maintenance and repair costs, vegetationmanagement or frequent repair of damage done byhigh-water events. High-maintenance approaches makelong-term success dependent upon human and financialresources that may not always be available. In addition tolimiting the need for maintenance, designing for self-sustainability also involves favouring ecological integrity.

An ecosystem in good condition is more likely to have theability to adapt to changes.

Use Passive Restoration, When Appropriate

Before actively altering a restoration site, determinewhether simply reducing or eliminating the sources ofdegradation and allowing time for recovery will beenough to allow the site to regenerate naturally. There areoften reasons for restoring a water body as quickly aspossible, but there are other situations when immediateresults are not critical. For some rivers and streams,

restoring the original hydrological regime may be enoto let time re-establish the native plant community, wits associated habitat value.

Restore Native Species and Avoid Non-Native

Species

Many invasive species out-compete native species becathey are expert colonizers of disturbed areas and lnatural controls. The temporary disturbance preduring restoration projects invites colonization invasive species that, once established, can undermrestoration efforts and lead to further spread of thinvasive species. Special attention should be givenavoiding the unintentional introduction of non-naspecies at the restoration site when the site is mvulnerable to invasion. In some cases, removal of nnative species may be among the primary goals of restoration project.

Use Natural Fixes and Bioengineering Techniques,

Where Possible

Bioengineering is a method of construction combining and dead plants or inorganic materials, to produce livfunctioning systems to prevent erosion, control sedimand other pollutants, and provide habitat. Bioenginee

techniques can often be successful for erosion control bank stabilization, flood mitigation and even wtreatment. Specific projects can range from the creatiowetland systems for the treatment of stormwater to restoration of vegetation on riverbanks to enhance natdecontamination of runoff before it enters the river.

Monitor and Adapt Where Changes

are Necessary

Every combination of watershed characteristics, source

stress, and restoration techniques is unique and, therefrestoration efforts may not proceed exactly as plann

Adapting a project to at least some change or new inmation should be considered normal. Monitoring beand during the work is crucial for finding out whetgoals are being achieved. If they are not, adjustmshould be undertaken. Post-project monitoring will hdetermine whether additional actions or adjustmentsneeded, and can provide useful information for fu



25/78

restoration efforts. This process of monitoring andadjustment is known as adaptive implementation oradaptive management (Appendix B). Monitoring plansshould be feasible in terms of costs and technology,and should provide information relevant to meeting theproject goals.

3. Lakes and Reservoirs

Lakes and reservoirs are components of many riversystems. They are typically dramatic and visually pleasingfeatures of a watershed or basin. They range frompond-sized water bodies to lakes stretching for hundredsof kilometres. Referred to by some as pearls on a river,lakes and reservoirs can have a significant effect on thequantity and quality of the freshwater that eventuallyreaches the oceans.

Seen from the shoreline, a large natural lake looksmuch the same as a large artificial reservoir, and bothoften contain the word lake in their name. Furthermore,the same principles of biology, chemistry and physicsapply to both. Indeed, it may be difficult to discern anyobvious differences between a lake and reservoir, butdifferences as well as similarities exist.

Lakes are water bodies formed by nature whereasreservoirs are artificial ones constructed by humans,

either by damming a flowing river or by diverting waterfrom a river to an artificial basin (impoundment). Somereservoirs are made by increasing the capacity of naturallakes. Many characteristics of lakes and reservoirs are afunction of the way in which they were formed and howhumans use their waters.

Lakes and reservoirs are important sources of fresh-water for agriculture, industry and municipalities. At thesame time, they provide habitats for a variety of species ofplants and animals. They are the sources of fish, areas formigratory birds to feed, reproduce or rest, and places we

all go for enjoyment and recreation. Considerable moneyas well as technical and scientific expertise is oftenrequired to keep them clean and healthy.

As human populations grow, greater demands areplaced on the services lakes and reservoirs provide. Thewater levels of many lakes and reservoirs have becomeconsistently lower as a result of higher consumptionby upstream agriculture, households and industries.Increasing numbers of people enjoy the recreational


activities these bodies can support, but this alters theirshores, changes the surrounding land use and cover, andincreases the amount of soil or sediments as well asnutrients reaching their waters. Finally, pollution fromadjacent lands and various point sources may increaseeutrophication processes and produce other non-desirable

effects such as increased concentrations of toxic algae,reduced dissolved oxygen and generation of foul odours.

3.1. Natural Lakes

Lakes are naturally-formed, usually bowl-shaped, depres-sions in the land surface that have filled with water overtime. These depressions were typically produced as a resultof glaciers, volcanic activity or tectonic movements. Theage of most permanent lakes is usually of a geological timeframe. Some ancient lakes may be millions of years old.

The most significant past mechanism for the formationof lakes in temperate areas was the natural process ofglacial scour, in which the slow movement of massivevolumes of glacial ice during and after the Ice Ageproduced depressions in the land surface that subse-quently filled with water. The North American GreatLakes (Superior, Michigan, Huron, Erie and Ontario),lakes in the Lake District of the United Kingdom, andthe numerous lakes in Scandinavia and Argentina areprominent examples of this type of lake formation. Some

smaller kettle lakes, as found on Cape Cod inMassachusetts, for example, were formed by the deposi-tion and subsequent melting of glacial ice blocks.

Another major lake formation process was tectonicmovement, in which slow movements of the earths crustgradually produced depressions that were subsequentlyfilled with water. Lake basins also formed as a result ofvolcanic activity, which also produced depressions in theland surface. Most of the earths very deep lakes resultedfrom either volcanic or tectonic activity. Lake Baikal inRussia, the worlds deepest lake, which contains approxi-

mately 20% of the worlds liquid freshwater, and theAfrican Rift Valley lakes are prominent examples of thistectonic type of lake formation.

Other natural processes that produced lake basinsinclude seepage of water down through layers of solublerock, erosion of the land surface by wind action, andplant growth or animal activity (such as beaver dams) thatresulted in blocking the outlet channels from shallowdepressions in the land surface.



26/78


There are literally millions of small lakes aroundthe world, concentrated largely in the temperate andsub-arctic regions. These regions are also characterizedby a relative abundance of freshwater. Many moreintermittent lakes occur in semi-arid and arid regions.

3.2. Constructed Reservoirs

In contrast to natural processes of lake formation, reservoirsare water bodies that are usually formed by constructing adam across a flowing river. A dam may sometimes alsobe constructed on the outlet channel of a natural lake as ameans of providing better control of the lakes water level(examples include Lake Victoria in Africa, and Lake Tahoein the United States). However, these latter water bodiestypically retain their natural lake characteristics.

Reservoirs are found primarily in areas with relativelyfew natural lakes, or where the lakes do not satisfy humanwater needs. Reservoirs are much younger than lakes, withlife spans expressed in terms of historical rather than geo-logical time. Although lakes are used for many of the samepurposes as reservoirs, a distinct feature of the latter is thatthey are usually built to address specific water needs. Theseinclude municipal and drinking water supplies, agriculturalirrigation, industrial and cooling water supplies, powergeneration, flood control, sport or commercial fisheries,recreation, aesthetics and/or navigation. Small reservoirs

are sometimes built for fire protection as well.The reasons for constructing reservoirs are ancient in

origin, and have focused on the need of humans to ensure amore reliable water supply and to protect themselves duringperiods of floods. Accordingly, reservoirs are usually foundin areas of water scarcity, or where a controlled water facil-ity was necessary. Small reservoirs were first constructedsome 4,000 years ago in China, Egypt and Mesopotamia,primarily to supply drinking water and for irrigationpurposes. Simple small dams were constructed by blockinga stream with soil and brush, in much the same manner as

beavers dam a stream. Larger reservoirs were constructed bydamming a natural depression, or by forming a depressionalong the river and digging a channel to divert water to itfrom the river. Early irrigation practices were linked largelyto land adjacent to streams. They required the constructionof larger dams that allowed humans to impound largervolumes of water. Later reservoirs were also used as sourcesof power, first to drive waterwheels and subsequently toproduce hydroelectric power.

3.3. Physical Characteristics

Like lakes, reservoirs range in size from pond-like to vlarge water bodies. The variations in type and shahowever, are much greater than for lakes. The treservoir includes different types of constructed w

bodies and/or water storage facilities. These are (1) vareservoirs, created by constructing a barrier (dam) ppendicular to a flowing river; and (2) off-river storreservoirs, created by constructing an enclosure parato a river, and subsequently supplying it with water eiby gravity or by pumping from the river. The latter revoirs are sometimes also called embankment or bounor pumped-storage reservoirs. They have controinflows and outflows to and from one or more rivers. example, much of the water in the river above NiagFalls between Canada and the United States is diverte

a pumped storage reservoir during the night and releathrough hydroelectric generators during the day whenenergy demand, and hence price, is higher.

In addition to single reservoirs, reservoir systems exist. These may be (1) cascade reservoirs, consisting series of reservoirs constructed along a single river; orinter-basin transfer schemes, designed to move wthrough a series of reservoirs, tunnels and/or canals frone drainage basin to another. These types are illustrain Figure A.24.

Much of our current limnological knowledge (incling that used to manage lakes and reservoirs) has cofrom studies of lakes over many decades. Althoughnow have a reasonable understanding of physical biological processes that take place in lakes, we less advanced in our understanding of these procein reservoirs. Many early reservoir studies focusedsediment loading from drainage basins. The rationalethis was that the rate at which a reservoir filled wsediment is a major determinant of useful operational Comparatively little attention was given to the envir

mental and socioeconomic issues associated wreservoir construction. That situation has changed.

3.3.1. Shape and Morphometry

The shape of lakes and reservoirs is determined larby how they were formed. This also affects some of tfundamental characteristics. Because lakes are naturaformed, bowl-shaped depressions typically located in



27/78

central part of a drainage basin, they usually have a morerounded shape than reservoirs. As in a bowl, the deepestpart of a lake is usually at its centre. The shallowest part ofthe water basin is usually located near the outflow channel.

In contrast, a reservoir often has its deepest part nearthe dam. Moreover, because a river often has a number ofstreams or tributaries draining into it, when it is dammedthe impounded water tends to back up into the tribu-taries. As a result, some reservoirs have a characteristicdendritic shape, with the arms radiating outwardfrom the main body of the reservoir as illustrated in

Figure A.25. In contrast, a reservoir formed by damminga river with high banks will tend to be long and narrow.Depending on how they were constructed, off-riverstorage reservoirs can have many shapes.

The dendritic or branching form of many reservoirsprovides a much longer shoreline than associated withlakes of similar volume. Reservoirs also usually have largerdrainage basins. Because of their larger basins and multi-ple tributary inputs, the flow of water into reservoirs ismore directly tied to precipitation events in the drainage

basin than it is in lakes. Also, the fact that the deepest partsof most reservoirs are just upstream of the dam facilitatesthe possibilities for draining the reservoir.

Damming a river inundates land previously abovewater, and sometimes forces the relocation of inhabitantsand wildlife living around the river. The presence of adam downstream also allows a greater degree of control ofwater levels and volumes for reservoirs than for lakes.Constructing water discharge structures at different levels


in the dam allows withdrawal or discharge of water fromselected depths in a reservoir. Selective withdrawal

(as shown in Figure A.26) has major implications for thewater-mixing characteristics and increases flushingpossibilities for reservoirs.

3.3.2. Water Quality

The characteristics of river water typically undergochanges as the water enters the lake or reservoir. Primarilybecause of reduced velocities, sediment and other

E020801x

Figure A.25. Characteristic dendritic shape of a large

reservoir created by a dam to the right of this figure.

A B C

impoundment

dam

cascade

reservoir

urban

and rural use

E020801w

Figure A.24. Types of reservoir

arrangements, ranging from

(left to right) a single reservoirto a cascade of reservoirs along

a river, to pumped storage

reservoirs adjacent to rivers.



28/78


materials carried in the water settle out in the lake or

reservoir. The structure of the biological communities alsochanges from organisms suited to living in flowing watersto those that thrive in standing or pooled waters. Pooledwaters provide greater opportunities for the growth ofalgae (phytoplankton) that can lead to eutrophication.

Reservoirs typically receive larger inputs of water, aswell as soil and other materials carried in rivers, than dolakes. As a result, they usually receive larger pollutantloads. However, because of greater water inflows, flushingrates are typically more rapid than in lakes (Figure A.27).Thus, although reservoirs may receive greater pollutant

loads, they have the potential to flush the pollut

wr- systems planning & mmt - 15_appendix_a

Documents