20 Rivers I - Rivers and Streams Watershed Total land area...

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Unformatted text preview: Rivers and Streams Watershed Total land area that drains surface water to a common point. Separated topographically from adjacent basins by a geographical barrier such as a ridge, hill or mountain, which is known as a water divide. 1/5 of rainwater falling a watershed collects directly in rivers 80% Evaporation Groundwater Lakes Sinks Soil Water Wetlands Large Watersheds Amazon Watershed ¾ the size of United States 2,720,000 sq mi World’s Largest Watershed 80 – 110 ‘’ rainfall/year 2000 The Amazon River largest river in the world by volume, with a total flow greater than the next top ten largest rivers combined. World Hydrology Mouth of Amazon Discharge: 319,000 m³ per sec. 20% of freshwater entering the oceans Watershed Biodiversity largest collection of living plants and animal species in the world 2.5 million insect species 2000 bird and mammal species 75,000 types of trees/km2 150,000 species of vascular plants/km2 1 in 5 10% of the World’s Terrestrial Primary Productivity Accumulated 0.62 tons of carbon per hectare per year between 1975 and 1996 $6820/hectare (intact) $1000/hectare (clear cut) $148/hectare (pasture) vanishing at a rate of 20,000 miles² per year Deforestation: releases 200 million metric tons of CO2/yr Congo Watershed 2nd Largest West Africa 1,335,000 mi2 700,000 mi2 of tropical rainforest Discharge: 41,800 m³/s Amazon: 319,000 m³/sec 3,000 mi lost each year 2 Mississippi Watershed 3rd Largest confluence mouth Discharge: 12,800 m3/sec 1,151,000 sq mi Watershed/River Components headwaters tributary Watershed (basin) confluence Headwaters: the source of the river mouth Mouth: end of river Confluence: the point where two rivers meet Tributary: a smaller river which flows into a larger river Length = headwaters to mouth Total Length of the Longest Rivers Nile = 4135 miles Amazon = 3980 miles Yangtze = 3917 miles Mouth of Nile Congo Mississippi/Missouri = 3902 miles Extra Credit 1. The largest watershed on earth is ______________ 2. The Amazon River is responsible for ___% of freshwater flow to the oceans. 3. The point where two rivers meet is a _______________ 4. The longest river in the world is ___________________ 5. The longest river in the U.S. is ____________________ River Flow Flow is from headwaters to mouth River flow is due to gravity. Flow velocity strongly depends on the altitude of the headwaters in relation to the mouth River Flow Rivers flow due to gravity. Flow velocity is quantified, in part, by differences in elevation over a lateral distance. This driving force for river flow is called a gradient, or the difference in elevation divided by the length source h L mouth Δh ΔL The Mississippi Source: Lake Itasca at 1475 feet Mouth: Gulf of Mexico at 0 feet Gradient Mississippi : headwaters = 1475 ft Lake Itasca mouth = 0 ft New Orleans length = 2330 miles Elevation: Length: Δh = 1475 feet – 0 feet = 1475 ft. ΔL = 2330 miles Δh ΔL = 1475 ft = 0.63 ft/mi 2330 mi Gradients of the Three Longest Rivers Lake Victoria Nile = 3721 ft = 0.9 ft/mile 4135 miles Andes Amazon = 16,962 ft = 4.24 ft/mile 3980 miles Tibet Plateau Yangtze = 16,542 feet = 4.17 ft/mile 3917 miles Large Gradient Δh ΔL source h L mouth Small Gradient Δh ΔL h source L mouth North Carolina Mountains 1600 ft = 213 ft/mi 7.5 mi 200 ft = 25 ft/mi 8.0 mi The gradient, in part, determines the flow velocity The gradient of the river is a dominant factor In river flow velocity Constrictions increase velocity Bottom roughness decreases flow velocity Winding or meandering rivers tend to flow more slowly Length decreases velocity, but increases volume and width Florida River Flow Apalachicola Suwannee St. Johns Kissimmee Generally sluggish flow Florida Elevation - Highest point - Mean - Lowest point 345 ft Britton Hill 98 ft 0 ft Florida’s Rivers River St. Johns Suwannee Kissimmee Apalachicola length 310 miles 266 miles 134 miles 112 miles Elevation 30 feet 200 feet 14 feet 77 feet Source Gradient 1.16 in/mile 9.02 in/mile 1.25 in/mile 8.25 in/mile Slow flow of contaminants St. Johns River “Laziest river in the world” 30 foot elevation change over 310 miles Gradient = 0.096 ft/mile (1.16 in/mile) Suwannee River Gradient: 0.75 ft./mile Origin: Okeefenokee Swamp Diverse Largely unspoiled The basin includes Lafayette and Suwannee counties, • residential and commercial septic systems in rural areas • about 300 row crop and vegetable farms, • 44 dairies with more than 25,000 animals • 150 poultry operations with more than 38 million birds Kissimmee 14 ft over 134 miles 0.1 ft/mile (1.25 in/mile) 0.25 ft/mile (3.0 in/mile) Kissimmee – Okeechobee – Everglades Floodplains Floodplain - area of relatively level land that is inundated from time to time by river flooding Floodplain Productivity and Fertility Wetting of the floodplain soil releases a surge of nutrients Primary productivity (photosynthesizers) stimulated Microscopic organisms thrive Increase in overall productivity up the food chain Larger species enter a rapid breeding cycle. Opportunistic feeders (particularly birds) move in The surge of new growth endures for some time. A floodplain can contain up to 1000 times as many species as a river Interaction of the river with the floodplain also can remove excess nutrients from the river water Kissimmee River Channelization Stabilized water levels and reduced flow eliminated river-floodplain interactions. Stabilized water levels largely eliminated adult spawning and foraging habitat, as well as larval and juvenile refuge sites for fish on the floodplain. Floodplain utilization by waterfowl declined by 92%. Some “Local” Rivers Suwannee River 55 springs Whitewater Rapids Withlacoochee River South on U.S. 41/121 Rainbow River Ichetucknee River North on U.S. 27 Santa Fe River Suwannee River Ichetucknee springs Lake Santa Fe Santa Fe River Disappearing River U.S. 441 north to High Springs Weeki Wachee River U.S. 19 south Development Contamination by human waste Next: Water Quality Optional Text: Clean Water by Kenneth M. Vigil (2nd edition) Floodplains and Levees Floodplains Floodplain - area of relatively level land that is inundated from time to time by river flooding Floodplain Productivity and Fertility Wetting of the floodplain soil releases a surge of nutrients Primary productivity (photosynthesizers) stimulated Microscopic organisms thrive Increase in overall productivity up the food chain Larger species enter a rapid breeding cycle. Opportunistic feeders (particularly birds) move in The surge of new growth endures for some time. A floodplain can contain up to 1000 times as many species as a river Interaction of the river with the floodplain also can remove excess nutrients from the river Floodplain Productivity: The Mekong and Tonle Sap Mekong 17,139 ft Gradient: 5.7 ft/mile 12th longest China, Thailand, Cambodia, Laos, Vietnam The least modified major river in the world Characterized by seasonal pulses of monsoon water Mekong River Lifeblood of S.E. Asia. 80% of Cambodia’s population is involved in fishing and processing of Mekong harvest. 60 million people in Laos, Cambodia, and Vietnam subsist on the river and its wetlands which yield approximately 2 million tons of fish per year: equal to 2% of the entire would catch of wild fish. The biological hearts of the river’s productivity are the Tonle Sap river and Tonle Sap Lake. Tonle Sap Mekong Tonle Sap The Tonle Sap river is a tributary to the Mekong The Tonle Sap lake is the source of the river Reversing its Flow Dry season from November to May Monsoon rains from June to September Mekong forces the tributary to flow backward into Tonle Sap Lake Absorbs 1/5 of the Mekong’s flood waters 1000 species of fish 2700 to 16,000 km2 Trey Riel 60% of the Cambodians' protein intake 6 X its normal area Juvenile fry are swept into the flooded forests of the Tonle Sap floodplain and feed on floating vegetation Nets surround the entire lake And river floodplain harvest the fish. Since the 12th Century Floodplains Gone Wrong High flow Low flow Altered flow Triggers spawning migrations in fish and gives them access to the variety of habitats needed for reproduction, feeding and growth of their young allow diverse plant beds to develop and thrive, providing important habitat for fish and wildlife connection between the river and its floodplains is lost. Plant and animal diversity declines, water quality is degraded and the damaging effects of flooding are increased The Kissimmee River floodplain utilization by waterfowl declined by 92%. The Mississippi June, 2008 Levee Levee Levees Natural or artificial embankments paralleling the course of a river Prevent natural floodplain function Next: Rivers and Wastes ...
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This note was uploaded on 02/24/2011 for the course SWS 2007 taught by Professor bonczek during the Fall '09 term at University of Florida.

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