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Chapter 3

Surface Water Hydrology

Prof. Dr. Ali El-NaqaHashemite UniversityJune 2013

Chapter 3: Surface Water HydrologyWhat is Surface Water Hydrology?WatershedsOverland FlowRiversLakesSediment Transport and DepositionWater MeasurementFlood Events

Figure 3.1 Leonardo da Vinci was fascinated by the similarities between the organization of rivers on the surface of the Earth and the human circulatory system.

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What is Surface Water Hydrology?The study of moving water found in rivers, open channels, lakes, and runoff across the open land surfaceImportant for transportation, irrigation, water supply, hydropower, etc.Related topics:Ground water (below the surface)Marine water (in the oceans)Icecaps and glaciers

WatershedsThe total land area that drains to a common point.Also called a river basin, drainage basin, or catchmentThe watershed is delineated by finding the watershed divide, or ridge, that separates the watershed from its neighbors

Figure 3.2 Mississippi River Watershed

Figure 3.5 The Mississippi River is the third largest drainage basin in the world, exceeded in size only by the watersheds of the Amazon River in South America and the Zaire River in Africa.

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Figure 3.3 Hills, valleys, and slopes of a topographic map.

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Topographic Maps: Used to show slope, elevation, distance, and physical featuresScale: Used to relate the distance on the map to the true distance. 1 map inch = 12,000 true inches = 2000 true feetContour Line: Used to show points of similar elevation.1000 foot contour line is a constant elevation above sea levelContour Interval: The distance between contour lines. A 20 foot contour interval has contours every 20 feet, i.e., 980, 1000, 1020, etc. Slope: The steepness of the groundA 1% slope is where the surface drops 1 foot every 100 feet.Aspect: The direction that the slope faces, North, South, East, West, etc.

Three Simple RulesSurface water generally flows at right angles (perpendicular) across contour linesRidges are indicated by the highest elevation contour lineDrainages are indicated by contour lines pointing downstream

Hillslope Flow

Overland FlowRain falls onto vegetation, and then to the ground. Interception is lost in the vegetationThroughfall makes it to the groundStemflow runs down the vegetationWater reaching the ground can:Accumulate in depressionsSoak into the ground (infiltration)Flow across the surface as overland flow

RiversComponents of a RiverHeadwaters: the source of the riverTributaries: smaller streams that combine at a confluenceUpstream vs. Downstream: related to the flow directionThalveg: Main part of river channelHyporheic Zone: Shallow ground-water flow below the river bed

River Morphology:Young, V shaped valleysOlder, U shaped valleysOldest, meandering channels with oxbow lakesBraided channels with lots of sedimentChannels are choked with sedimentsBelow glacial terrainIn wetlands where there is very low gradient (slope)

Figure 3.4 Changes in stream properties along a watershed.

Types of RiversEphemeral: flows only during stormsIntermittent: flows seasonallyLosing stream: loses flow to groundwaterGaining stream: gains water from the subsurfaceGradient: the slope or fall of the river, usually decreases as the river gets larger.

Figure 3.6 Cross section of a gaining (or effluent) stream, common in humid regions, and a losing (or influent) stream, often found in arid or semiarid locations.

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Table 3.2 Largest Lakes in the World

LakesAny body of water (other than an ocean) that is of reasonable size, impounds water, and moves very slowlyTypes of lakes:cirques: formed in mountains by glacierspluvial: formed in desertskettles: formed by buried glacial ice that meltedLake productivityoligotrophic: very low productivity, cleareutrophic: very high productivity, green

Ecologic Zoneslittoral: along the shorelinelimnetic: near the surface in the deeper partsprofundal: near the bottom in the deeper partsThermal Cyclesepiliminion: near the surface, warm in summerhypolimnion: near the bottom, cold in summerthermocline: boundary between epi- and hypolimnionlake turnover: in fall when epi- and hypolimnion mixSeiche: Wind driven water level fluctuations

Figure 3.8 Seasonal layering and turnover in a lake at mid-latitudes.

Figure 3.9 Rivers have a profound effect on landforms.

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Sediment Transport and DepositionThis refers to soil carried by water and then deposited in low energy environments.The heavy sediments (sands) fall out along the river banks, forming leveesFiner materials (clays and silts) fall out in flood plainsYazoo rivers parallel the main riverA delta forms where the sediment chokes the main channel - often in braided rivers.

VelocityHigh energy streams have high velocitiesHigher velocities can carry more, and larger particlesSorting occurs when large particles are left behind, and small particles are carried awaySediment LoadThe total material carried, composed of:Suspended load: fine materials carried as particlesDissolved load: materials that are in solutionBedload: larger materials carried along the bottomSediment Yield: The load per unit area

Figure 3.11 Steep gradients and high water velocity are great combinations for moving boulders, sediment, and kayakers.

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Water MeasurementRational FormulaQ = C i AQ is the peak runoff rate, cfsC is the runoff coefficientUrban areas, C = 0.9Industrial areas, C = 0.8Residential areas, C = 0.6Forested areas, C = 0.1i is the rainfall intensity, in/hrA is the watershed area, acres

River DischargeDischarge is the flow of waterMeasured in units of cubic feet per minute, or cfsThe metric equivalent is liters per second, or LpsWe find the discharge, Q, by taking the product of the velocity, v, and the area, A:Q = V AExample, if the width of the channel is ten feet, the depth is one foot, and the velocity is two feet per second, then A = 10 ft x 1 ft = 10 ft2 Q = 2 ft/s x 10 ft2 = 20 cfs

Figure 3.10 One cubic foot per second, or cfs (or one cubic meter per second, or cms) is equivalent to one cubic foot (or meter) of water flowing past a given point in a one-second time interval.

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The water velocity is found using a flowmeter, which looks like an anemometer:

Figure 3.13 The hydrograph of a river can look similar to this example after a brief but intense rainfall event.

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To make things easy, we use a staff gage (or ruler) to measure the river stage (how high the river is.We use a rating curve to relate the discharge to the river stage.

Water Storage in Lakes and ReservoirsWe normally measure large volumes of water in units of Acre-Feet1 acre-foot is the volume of water that covers one acre to a depth of one footLake Lanier, when full, has 2,000,000 acre-feet of water. It covers 40,000 acres with an average depth of 50 feet.We keep track of the volume using the stage-capacity curve:The storage goes down as the water level, or stage, goes down

Flood EventsFlood frequency: the likelihood that a large flood will happen100-year flood: flood that is exceeded - on average - once every 100 years, the probability in 1 year is 1/100 = 1 %10-year flood: probability = 10 %Mean annual flood:exceeded once every two years, probability = 50%

Figure 3.15 Flood damage can be predicted based on the intensity of a storm and the topography of a region.

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Extreme EventsProbable Maximum Precipitation (PMP)The most extreme rainfall possibleUsed for estimating the effects of extreme weatherProbable Maximum Flood (PMF)The most extreme flood possibleUsed for estimating maximum extent of flooding

GIS MappingGeographic Information Systems (GIS):Used to organize spatial informationVarious properties are stored in the computerGIS layers include topography, soils, hydrography, vegetation, land use, etc.

Figure 3.16 A GIS map display showing the schools in a town. Notice that a query of Elmar High School was made, and the corresponding attribute data and digital image are shown.

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Figure 3.17 Streams, lakes and medical facilities are added to the original map display.

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Figure 3.19 With the Q100 layer added to the map display, it is easy to see that Edwards Elementary is the only school in the 100-year floodplain.

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Quiz 3If the Oconee River is flowing at a rate of 1000 ft3/s, how long would it take to fill this room?Use the tape measure provided to measure the length, width, and height of the room, and calculate the volume, in cubic feet. [Use L = 60, W = 100, H = 12]Calculate the time by dividing the volume (ft3) by the flow rate (ft3/s), giving you the time, in seconds.Delineate (draw the boundary around) the Oconee River Watershed using the map found at: www.hydrology.uga.edu/Georgia.pdfTrue - False Questions:[T / F] Overland flow is more likely in forested watersheds because it rains harder there[T / F] Urban areas have higher runoff peaks than agricultural areas[T / F] Sand is easier for rivers to carry than clays[T / F] A 100-year flood has a 1 percent chance of happening in any one year[T / F] The Probable Maximum Precipitation is the largest observed rain in a year.If Athens is located 300 river miles from the coast, and the river flows at a rate of 3 miles per hour, how long will it take the water to reach the ocean?For the previous problem, what would happen if there is a lake between Athens and the coast?