GNR 639 GNR 624 : Water Resource and River basin management Lesson 4 River characterization Prof. R. Nagarajan, CSRE , IIT Bombay
Importance of drainage basins Geopolitical boundaries - historically important for determining territorial boundaries, in regions where trade by water has been important. Hydrology - the drainage basin is a logical unit of focus for studying the movement of water within the hydrological cycle, because the majority of water that discharges from the basin outlet originated as precipitation falling on the basin. Measurement of the discharge of water from a basin may be made by a stream gauge located at the basin's outlet. Geomorphology - Drainage basins are the principal hydrologic unit considered in fluvial geomorphology. A drainage basin is the source for water and sediment that moves through the river system and reshapes the channel. Ecology - water flows pick up nutrients, sediment, and pollutants and transported towards the outlet of the basin. It affects the ecological processes along the way as well as in the receiving water source. Resource management - Because drainage basins are coherent entities in a hydrological sense, it has become common to manage water resources on the basis of individual basins. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management Drainage basin is an extent or an area of land where surface water from rain, melting snow, or ice converges to a single point at a lower elevation, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean. River basin is used to describe an area that drains Into larger river/ocean. Larger rivers are interconnected watersheds. Watershed describe an area that drains into a Smaller river or stream. Source courtesy: slideplayer.com Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management Source Courtesy: Indiana.edu Prof. R. Nagarajan, CSRE , IIT Bombay
River basin components Source courtesy: iss.k12.uc.us Catchment area Command area Coastal area Issues in river basin Rainfall & water availability Storage & distribution Sharing in space & time – quantity & quality
GNR 639 GNR 624 : Water Resource and River basin management Prof. R. Nagarajan, CSRE , IIT Bombay
Factors influencing river basin system • Size • Shape • Physiography • Climate • Drainage • Land use • Vegetation • Geology and Soils • Hydrology • Hydrogeology • Socioeconomics 10.1
GNR 639 GNR 624 : Water Resource and River basin management River Basin structure Components of river basin Catchment area Utilization area – command area Coastal area Issues in river basin Rainfall & water availability Storage & distribution Sharing in space & time – quantity & quality Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management Prof. R. Nagarajan, CSRE , IIT Bombay
River types Perennial river – flow throughout the year • Permanent rivers • Exotic rivers Non-Perennial rivers – flow in rainy seasons • Periodic rivers • Episodic river Channel types Source courtesy: acegeography.com • Straight channel Source courtesy: acegeography.com • Braided channel numerous distinct channels that repeatedly divide and then merge again downstream • Meander channel consists of single main channel that bends and loops
GNR 639 GNR 624 : Water Resource and River basin management Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management Catchment factors Topography - plays a big part in how fast runoff will reach a river. Rain that falls in steep mountainous areas will reach the primary river in the drainage basin faster than flat or lightly sloping areas (e.g., > 1% gradient). Shape - Shape will contribute to the speed with which the runoff reaches a river. A long thin catchment will take longer to drain than a circular catchment. Size will help determine the amount of water reaching the river, as the larger the catchment the greater the potential for flooding. It also determined on the basis of length and width of the drainage basin. Soil type will hel determine how much water reaches the river. Certsandy soils are very free-draining, and rainfall on sandy soil is likely to be absorbed by the ground. soils containing clay can be almost impermeable and therefore rainfall on clay soils will run off and contribute to flood volumes. If the surface is impermeable the precipitation will create surface run-off which will lead to higher risk of flooding; if the ground is permeable, the precipitation will infiltrate the soil. Land use can contribute to the volume of water reaching the river, in a similar way to clay soils. rainfall on roofs, pavements, and roads will be collected by rivers with almost no absorption into the groundwater. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management • Water in the form of rain or snow falling returns to the atmosphere by evaporation from the leaves of plants and from the ground, and by transpiration by plants. • Surplus water eventually makes its way through the drainage system - stored first on the surface, in depressions and ponds, or in the soil as soil moisture and groundwater. • Overland flow, occurs when not all the precipitation can infiltrate the soil. It moves quickly to streams and rivers. Infiltrated water moves more slowly — as through flow and interflow in partially saturated soils, and as groundwater flow in saturated soils. • Basin channel run-off is the combined result of quick flow (overland flow plus interflow) and base flow (groundwater flow). Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management Types of flow in stream channel Laminar flow - Under very low velocities water flows through a stream as smooth sheets running parallel to the bed In this type of flow the direction of water in the stream is not altered in its direction. Only the finest particles kind be detached, so laminar flow is basically non erosive. Turbulent flow - under higher flow velocities, resistance within the flow and that caused by the bed and sides of the channel (channel topography) cause the flow to break down into separate currents. - More erosive than laminar flow and help suspend material in the stream. Helical flow - spiral flow in a stream, Caused by channel shape. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management Stream Gradient – the downhill slope of the stream bed. The difference in elevation between two points on a stream divided by the distance between them. The stream gradient is one of the factors that controls a stream’s velocity. The steeper the slope, the faster the velocity of flow and the more the energy of the stream will be to erode materials Channel Shape and Roughness - The shape of the channel also controls stream velocity. In wide, shallow channel water flow slowly and in narrow channel it flows rapidly. The roughness of the channel also controls velocity. Roughness creates more friction and slows flow. Roughness of the channel In streams in humid climates, discharge increases in the downstream as river water evaporates into the air and soaks into the dry ground. In an arid climate, a river’s discharge can decrease in a downstream direction as 1. Water flows out of the ground into the river through the streambed. 2. Small tributary streams flow into a larger stream along its length, adding water to the stream as it travels. Discharge - is the volume of water that flows past a given point in a unit of time. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 624 : Water Resource and River basin management WEATHERING Freeze Thaw • Water enters cracks, freezes and expands. Ice thaws. Weakens rocks. Most effective in areas where the temperature fluctuates around 0 C during the diurnal range. Biological Weathering • Growing trees or animals dislodge or break up rock. Chemical Weathering • Chemicals break down rocks into smaller pieces which can fall into the river. Acid rain on limestone is an example. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 624 : Water Resource and River basin management GNR 639 River Erosion Attrition is the collision of rock fragments in the water against one another. The rocks are broken into smaller pieces and become smoother the longer the process continues. Abrasion is the grinding of rock fragments carried by the river against the bed and banks of the river. causing the channel to widen and deepen. This grinding is most powerful in flood time. In Hydraulic action rocks are dragged away from the bed and banks by the force of the running water. Corrosion/solution is the process by which river water reacts chemically with soluble minerals in the rocks and dissolves them. River Erosion is dependent on Stream velocity – the distance water travels in a stream per unit time and material through which it flows. Prof. R. Nagarajan, CSRE , IIT Bombay
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