Science of Water : Concepts and Applications

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Water Ecology 177 long profi le, cross-section, depth and slope profi le, and because these mutually adjust over a time scale as short as years and as long as centuries or more, cause-and-effect relationships are diffi cult to establish. Other variables that are presumed to interact as the stream achieves its graded state include width and depth, velocity, size of sediment load, bed roughness, and the degree of braiding (sinuosity). STREAM PROFILES Mainly because of gravity, most streams exhibit a downstream decrease in gradient along their length. Beginning at the headwaters, the steep gradient lessens as one proceeds downstream, resulting in a concave longitudinal profi le. Though diverse geography provides almost unlimited variation, a lengthy stream that originates in a mountainous area typically comes into existence as a series of springs and rivulets; these coalesce into a fast-fl owing, turbulent mountain stream, and the addition of tributaries results in a large and smoothly fl owing river that winds through the lowlands to the sea. When studying a stream system of any length, it becomes readily apparent (almost from the start) that what we are studying is a body of fl owing water that varies considerably from place to place along its length. For example, a common variable—the results of which can be readily seen— is whenever discharge increases, causing corresponding changes in the stream’s width, depth, and velocity. In addition to physical changes that occur from location to location along a stream’s course, there are a legion of biological variables that correlate with the stream size and distance downstream. The most apparent and striking changes are in steepness of slope and in the transition from a shallow stream with large boulders and a stony substrate to a deep stream with a sandy substrate. The particle size of bed material at various locations is also variable along the stream’s course. The particle size usually shifts from an abundance of coarser material upstream to mainly fi ner material in downstream areas. SINUOSITY Unless forced by man in the form of heavily regulated and channelized streams, straight channels are uncommon. Stream fl ow creates distinctive landforms composed of straight (usually in appearance only), meandering, and braided channels, channel networks, and fl ood plains. Simply put: fl owing water will follow a sinuous course. The most commonly used measure is the sinuosity index (SI). Sinuosity equals 1 in straight channels and more than 1 in sinuous channels. Meandering is the natural tendency for alluvial channels and is usually defi ned as an arbitrarily extreme level of sinuosity, typically a SI greater than 1.5. Many variables affect the degree of sinuosity. Even in many natural channel sections of a stream course that appear straight, meandering occurs in the line of maximum water or channel depth (known as the thalweg). Keep in mind that a stream has to meander, that is how they renew themselves. By meandering, they wash plants and soil from the land into their waters, and these serve as nutrients for the plants in the rivers. If rivers are not allowed to meander, if they are channelized, the amount of life they can support will gradually decrease. That means less fi sh, ultimately—and less bald eagles, herons, and other fi shing birds (Cave, 2000). Meander fl ow follows predictable pattern and causes regular regions of erosion and deposition (see Figure 6.15). The streamlines of maximum velocity and the deepest part of the channel lie close to the outer side of each bend and cross over near the point of infl ection between the banks (see Figure 6.15). A huge elevation of water at the outside of a bend causes a helical fl ow of water towards the opposite bank. In addition, a separation of surface fl ow causes a back eddy. The result is zones of erosion and deposition, and this explains why point bars develop in a downstream direction in depositional zones.
178 The Science of Water: Concepts and Applications FIGURE 6.15 A meandering reach. (a) High flow Intermediate flow Low flow Riffle (b) BARS, RIFFLES, AND POOLS Line of maximum velocity Pool Pool Riffle Deposition Water surface Riffle Pool Erosion FIGURE 6.16 (a) Longitudinal profi le of a riffl e-pool sequence. (b) Plain view of riffl e-pool sequence. Implicit in the morphology and formation of meanders are bars, riffl es, and pools. Bars develop by deposition in slower, less competent fl ow on either side of the sinuous mainstream. Onward moving water, depleted of bed load, regains competence and shears a pool in the meander—reloading the stream for the next bar. Alternating bars migrate to form riffl es (see Figure 6.16). As stream fl ow continues along its course, a pool-riffl e sequence is formed. The riffl e is a mound or hillock and the pool is a depression. Riffle Pool Riffle Pool Pool
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Second Edition THE SCIENCE OF WATER
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Cover Image: Falling Spring at Fall
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Contents Preface ..................
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Contents ix Velocity Head .........
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Contents xi Specifi c Conductance .
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Contents xiii (5) Beetles (Order: C
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Contents xv Chlorine Residual Testi
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Contents xvii Water Filtration Calc
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To the Reader In reading this text,
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1 Introduction When color photograp
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Introduction 3 On second look, we s
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Introduction 5 As mentioned earlier
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Introduction 7 This scream of lost
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Introduction 9 Metcalf & Eddy, Inc.
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12 The Science of Water: Concepts a
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3 Water Hydraulics Anyone who has t
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Water Hydraulics 47 Another relatio
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Water Hydraulics 49 • • 1 ft 3
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Water Hydraulics 51 √ Important P
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Water Hydraulics 53 FIGURE 3.4 Thru
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Water Hydraulics 55 Example 3.8 Pro
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Water Hydraulics 57 FIGURE 3.6 Lami
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Water Hydraulics 59 With regard to
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Water Hydraulics 61 or hydraulic gr
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Water Hydraulics 63 E 1 smaller fl
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Water Hydraulics 65 √ Note: In de
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Water Hydraulics 67 • Cone of dep
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Water Hydraulics 69 • • • •
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Water Hydraulics 71 The Darcy-Weisb
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Water Hydraulics 73 Of course, pipe
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Water Hydraulics 75 In this section
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Water Hydraulics 77 Slope (S) The s
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Water Hydraulics 79 and important c
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Water Hydraulics 81 and the depth o
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Water Hydraulics 83 TYPES OF DIFFER
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Water Hydraulics 85 √ Important P
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Water Hydraulics 87 Meter backpress
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Water Hydraulics 89 VELOCITY FLOWME
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Water Hydraulics 91 The positive-di
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Water Hydraulics 93 Solution: 1200g
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Water Hydraulics 95 Water and Waste
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100 The Science of Water: Concepts
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Page 180 and 181: 6 Water Ecology The subject of man
Page 182 and 183: Water Ecology 157 The environment i
Page 184 and 185: Water Ecology 159 FIGURE 6.2 Notone
Page 186 and 187: Water Ecology 161 H 2 O O 2 FIGURE
Page 188 and 189: Water Ecology 163 FeS FIGURE 6.6 Th
Page 190 and 191: Water Ecology 165 Algae FIGURE 6.8
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Page 212 and 213: Water Ecology 187 UNITS OF ORGANIZA
Page 214 and 215: Water Ecology 189 FIGURE 6.20 Stone
Page 216 and 217: Water Ecology 191 FIGURE 6.22 Midge
Page 218 and 219: Water Ecology 193 FIGURE 6.25 Riffl
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Page 222 and 223: Water Ecology 197 FIGURE 6.32 Damse
Page 224: Water Ecology 199 Darwin, C., 1998.
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10 Water Treatment Calculations Gup
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