River characterization Prof. R. Nagarajan, CSRE , IIT Bombay - - PowerPoint PPT Presentation

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

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

• f 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.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

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

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Source Courtesy: Indiana.edu

River basin components  Catchment area  Command area  Coastal area Issues in river basin  Rainfall & water availability  Storage & distribution  Sharing in space & time – quantity & quality

Source courtesy: iss.k12.uc.us

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

10.1 Factors influencing river basin system

• Size
• Shape
• Physiography
• Climate
• Drainage
• Land use
• Vegetation
• Geology and Soils
• Hydrology
• Hydrogeology
• Socioeconomics

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

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

River Basin structure

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

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

• Straight channel
• Braided channel numerous distinct channels that repeatedly divide and then merge again downstream
• Meander channel consists of single main channel that bends and loops

Source courtesy: acegeography.com

Source courtesy: acegeography.com

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

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.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

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
• n 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).

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

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.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Stream Gradient – the downhill slope of the stream bed. The difference in elevation between two points

• n 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.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

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.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

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.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : River basin management

WATER AS AN AGENT OF DEGRADATION

Running water is the important geologic agent in eroding, transporting and depositing sediment. Landscape is the result of stream erosion or deposition. Water erosion is a process involving the detachment and transport of weathered materials. Surface Erosion - Water moving on the surface without being confined to a channel. The two forms are : splash and sheet erosion . Splash Erosion - First step in the erosion process. Raindrops typically fall with a velocity of 20-30 feet per second. Disaggregating and displacement of wet surface soil creating small craters in bare soil. Energy of these impacts is sufficient to displace soil particles as high as two feet vertically Sheet Erosion - Gradual removal of a uniform layer of soil from the surface. Entrainment of loose particles in overland flow. dependent on the soil type, velocity, vegetation, gradient and volume of flow over the surface. Long slopes, steep slopes, and slopes that carry higher volumes of runoff are more susceptible to sheet erosion Channel Erosion - Water is confined to long trough-like depressions called channel Rill Erosion - The first stage of channel erosion and intermediate process between sheet and gully erosion. They are many closely spaced, innumerable and small shallow channels eroded by threads of turbulent flow Gully Erosion - Larger versions of rills. Most gullies extend up slope as a result of headwall migration. It is the collapse and slumping

• f the sidewalls, which usually contributes the greatest proportion of soil loss.

Stream Erosion - Eventually gullies develop into streams. Streams/Rivers contain more water and have more capacity to do the work of erosion, transportation and deposition. Stream channel erosion consists of both streambed and stream bank erosion.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

River Deposition - A river drops its load when the speed or volume of the river decreases or competence is reduced. Competence - the size of the largest particle that can be transported by a stream. Capacity - the maximum load that a stream could transport under given conditions; its potential. -The heavier material is deposited first and the finer material carried further. Rivers reduce their speed when they enter flat land, enters a lake or the sea or reach an arid area or with change in gradient or as channel widens or changes direction. The volume can be reduced during a dry season or when the river passes over more porous landscapes e.g. sand or limestone. Some of the depositional land forms include levees, flood plain, delta, alluvial funs, back swamp, point bars and etc. Materials deposited by river are known as

• Alluvium. -Most alluvium is deposited into quiet water (ocean or lake).

Rivers Transport their Sediments

• Pebbles, Cobbles and Boulders (Bedload):Travel by rolling, sliding and bouncing along the

streambed.

• Sand-Sized Particles (Bedload):Move by Saltation. Small grains bounce along the river bottom, in

a colliding and jumping motion.

• Silts and Clay(Suspended Load):These are carried in Suspension.
• Salts and Ions (Dissolved Load):Are carried in Solution.

Sediment Speed

• Sediments never travel faster than the river water itself.
• Dissolved salts travel at the same speed as the water.
• Bedload and suspended sediments always travel slower than the river water.

Increased River Velocity = Larger Sediments + Increased Volume of Sediments + Increased Erosion Decreased River Velocity = Smaller Sediments + Decreased Volume of Sediments + Increased Deposition

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Sediment Transport - A river carries or transports eroded materials such as mud, sand, boulders and dissolved materials on its journey. These materials are known as its load. Bed load: heavy sediment particles that travel on the streambed - sand and gravel. These particles move along the bottom, travel individually or in groups. They will be deposited whenever the local flow conditions will not entrain. Suspended load: are fine or light enough to remain lifted indefinitely above the bottom by the water turbulence. e.g. silts and clays . Dissolved load: soluble products of chemical weathering process can make up a substantial dissolved load in a

• stream. Most streams contain numerous ions in solution. Such as bicarbonate, calcium, potassium, sodium, chloride,

and sulphate. Generally, most material is transported in the suspended load; the least, in bed load. The load is carried along by four processes Traction is where boulders or stones are rolled or sliding along the stream bed by the force of the water Saltation: the speed of the water lifts the fragments (tiny pebbles ) of the river bottom, and they bounce along and leapfrog over each other. It is a combination of traction and suspension. Suspension is when very fine particles (clay, silt and fine sand) are carried along in the river. The small particles are held up by the water as they float because they are very, very small

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Drainage system is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land. Geo-morphologists and hydrologists often view streams as being part of drainage basins. A drainage basin is the topographic region from which a stream receives runoff, through flow, and groundwater flow. Drainage basins are divided from each other by topographic barriers called a watershed. A watershed represents all of the stream tributaries that flow to some location along the stream channel. The number, size, and shape of the drainage basins found in an area varies and the larger the topographic map, the more information on the drainage basin is available

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Hypsometric analysis Source courtesy: www2.geog.soton.ac.uk

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

• The river systems within drainage basins are a type of network, and it is networks that can be analyzed

with respect to either topological or geometrical properties.

• Topology is a branch of geometry referring to certain spatial relationships between phenomena, e.g.

relative position and contiguity, rather than those of distance or direction.’ (Whittow, 1994).

• Topology focuses on the structural nature of a network, rather than its geometrical form, and is

therefore often particularly useful when analysing function and process.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

TYPE STRUCTURAL CONTROL

Dendritic Lack of structural control; rock/sediment of uniform resistance Parallel Closely spaced faults; steep topography; non-cohesive (erodible) sediments Radial Volcanic cones, domes Trellis Tilted or folded alternately resistant/weak sedimentary units Rectangular Joints or faults Annular Eroded dome in alternate resistant/weak sediments Centripetal Calderas, craters, tectonic basins Deranged Glaciated or highly disturbed terrain

Drainage pattern Source courtesy: www2.geog.soton.ac.uk

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

• Streams tend to form drainage patterns: dendritic, rectangular, radial, centripetal, and trellis. The

patterns result from the type of soil in the area of drainage and the erosion of the soil by flowing water.

• Dendritic, branching patterns form in areas of flat sedimentary rock, while areas with high central peaks,

such as volcanoes, exhibit radial drainage patterns.

• Water flows into a bowl- shaped valley by centripetal drainage and creates a lake, or erodes areas

between ridges to create deep valleys, as seen in trellis drainage.

• Where run-off concentrates, the land surface is eroded to form a channel. Drainage channels form a

network that collects water from all parts of the basin and carries it to a single river at the basin outlet.

• The pattern formed by the network is influenced by climate and land relief, but the underlying geological

structure is usually the most important determining factor.

• Drainage patterns are generally so closely related to geology that they are widely used by geophysicists

to identify rock faults and interpret structure.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

The geometry of a trellis drainage system is similar to that of a common garden trellis used to grow vines. As the river flows along a strike valley, smaller tributaries feed into it from the steep slopes on the sides of mountains. These tributaries enter the main river at approximately 90 degree angles, causing a trellis-like appearance of the drainage system. Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America Rectangular drainage develops on rocks that are of approximately uniform resistance to erosion, but which have two directions

• f jointing at approximately right angles. The joints are usually less resistant to erosion than the bulk rock so erosion tends to

preferentially open the joints and streams eventually develop along the joints. The result is a stream system in which streams consist mainly of straight line segments with right angle bends, and tributaries join larger streams at right angles. In a radial drainage system the streams radiate outwards from a central high point. volcanoes usually display excellent radial

• drainage. Other geological features on which radial drainage commonly develops are domes and laccoliths. On these features

the drainage may exhibit a combination of radial and annular patterns. A deranged drainage system is a drainage system in drainage basins where there is no coherent pattern to the rivers and lakes. It happens in areas where there has been much geological disruption. The classic example is the Canadian Shield. During the last ice age, the topsoil was scraped off, leaving mostly bare rock. The melting of the glaciers left land with many irregularities

• f elevation, and a great deal of water to collect in the low points, explaining the large number of lakes which are found in
• Canada. The watersheds are young and are still sorting themselves out. Eventually the system will stabilize

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Strahler’s stream ordering

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GNR 624 : Water Resource and River basin management

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Important Watershed Characteristics Drainage Area (A) is the probably the single most important watershed characteristic for hydrologic design. It reflects the volume of water that can be generated from rainfall. Watershed Length (L) of a watershed is the second watershed characteristic of interest. The length of a watershed is important in hydrologic computations. Watershed length is usually defined as the distance measured along the main channel from the watershed outlet to the basin divide. The straight-line distance from the outlet point on the watershed divide is not usually used to compute L because the travel distance of floodwaters is conceptually the length of interest. Thus, the length is measured along the principal flow path. Since it will be used for hydrologic calculations, this length is more appropriately labeled the hydrologic length. Watershed Slope Slope is an important factor in the momentum. Both watershed and channel slope may be of

• interest. Watershed slope reflects the rate of change of elevation with respect to distance along the principal flow
• path. Typically, the principal flow path is delineated, and the watershed slope (S) is computed as the difference in

elevation (E) between the end points of the principal flow path divided by the hydrologic length of the flow path (L): S = E/L

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Watershed Shape have variety of shapes reflecting the way that runoff will “bunch up” at the outlet. A circular watershed would result in runoff from various parts of the watershed reaching the outlet at the same time. An elliptical watershed having the outlet at one end of the major axis and having the same area as the circular watershed would cause the runoff to be spread

• ut over time, thus producing a smaller flood peak than that of the circular watershed.

The following are a few typical parameters: Length to the center of area (Lca): the distance in miles measured along the main channel from the basin outlet to the point on the main channel opposite the center of area. Shape Factor (Ll) Ll = (LLca)0.3 Where L is the length of the watershed in miles Circularity ratio (Fc): Fc = P/(4A)0.5 Where P and A are the perimeter (ft) and area (ft2) of the watershed, respectively. Circularity ration (Rc): Rc = A/Ao Where A0 is the area of a circle having a perimeter equal to the perimeter of the basin. Elongation Ration (Re): Re = 2/Lm(A/)0.5 Where Lm is the maximum length (ft) of the basin parallel to the principal drainage lines. Generally, the shape factor (Ll) is the best descriptor of peak discharge. It is negatively correlated with peak discharge (i.e. as the Ll decreases, peak discharge increases)

Source courtesy: coolgeography.co.uk

Youthful River:

• River flowing down a steep gradient.
• Channel is V-shaped due to down cutting rather than lateral erosion.
• Velocity is fast and strong and Capable of moving all sediment sizes from

ions in solution, to silts and clays, also cobbles and boulders.

• Steep sided cliffs flank the river.
• floodplain does not exist. There are no grassy areas beside the river
• Rapids may be present due to the water velocity and the presence of

boulders in the channel. Waterfalls are also a feature of a young river.

• Erosion is prominent over deposition

Source courtesy: sswm.info

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Streams develop their valley through Down cutting – the process of deepening a valley by erosion of the streambed. it can cut a narrow slot canyon down through the rock. The limit of down cutting is known as base level; Lateral erosion is a stream deepening its channel by cutting while part of its energy is also widening the valley by lateral erosion. The erosion of a stream’s bank and valley walls as the stream swings from side to side across its valley floor. Head ward erosion :a stream can also lengthen its valley by head ward erosion. The slow uphill growth of a valley above its original source through gulling, mass wasting, and sheet erosion. Stream capture is an event where a portion of the flow of one stream is diverted into that of another by natural processes. Graded stream has regulated its depth, width, slope, velocity, etc. for flow and sediment transport in maintain a steady-state condition. Characterised by slope of the longitudinal profile is concave upward, steeping upstream, absence of falls within the channel profile and no net erosion or deposition occurs along its channel. Non-graded stream Energy within the system is not evenly distributed along the profile; contains falls and

• basins. Falls result in a concentration of energy, which promotes erosion.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Young Stage of a river has steep-sided and narrow V-shaped valley created by vertical erosion characterized by waterfalls and rapids. Water is often quite clear because the river is not carrying much load in suspension. Velocity is high; Down cutting and head ward erosion are the major processes of river erosion and head ward erosion is dominant V shaped Valley profile in the upper course Long Profile of a typical stream is a depiction of the down slope gradient of stream. Gorge is a steep, V-shaped valley formed by the vertical (down ward) erosion of the land by the river. The Indus Gorge in Kashmir is the deepest in the world (about 5180 m.). If the region is arid where there is little weathering and mass wasting on the valley sides, the gorge will be impressively deep. If such a gorge is deep, long and U- shaped, we call it canyon. Canyon is deepened more than they are widened. Slot-canyon: Young stream, eroding down and no mass wasting.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

RAPIDS

• Found where there is a sudden increase in the slope of the slope of the channel or where the river

flows over a series of gently dipping harder bands of rock

• As the water becomes more turbulent its erosive power increases.

WATER FALLS

• Found where there are marked changes in geology in the river valley.
• Where resistant rocks are underlain by less resistant beds, the plunge pool at the foot of the fall

experience the force of the swirling water around the rocks, leading to more erosion

• This undercuts the beds above, leaving them overhanging and prone to collapse
• The waterfall therefore retreats upstream.

PROCESS AND IMPACT OF REJUVENATION

• Causes the river to increase its down cutting activity.
• Isostatic or eustatic change result in increased amounts of energy available to the river for erosive

processes, because it has to go down further to reach the base level.

• The river is working towards having a smooth gradient down its course.
• Knick points are breaks in gradient along the profile, usually marked by rapids or waterfalls. This

signifies the current progress of regression

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Potholes

• Circular depression on the river bed carved out of solid rock.
• Formed by a drilling action as pebbles are caught in eddy currents and whisked around

within a small natural crack or hollow.

• As time passes, the drilling action enlarges the hollow to form a pothole.
• Commonly found below waterfalls or rapids, where hydraulic action is a significant

process.

Rapids

• Small series of waterfalls associated with very disturbed turbulent water.
• Forms when rocks or varying resistances cut across a valley and erosive process create a series of

steps.

Waterfalls

• Sudden step in a river’s long profile.
• Often the result of a tougher, more resistant band of rock cutting across the valley.
• Unable to erode the rock at the same rate as neighbouring rocks, a step is formed and a waterfall

results.

Mature River

• River flows down a moderate gradient.
• Channel is U-shaped due to moderate downcutting but also lateral erosion
• Velocity is greater than an old age river but less than a youthful one
• Capable of moving many sediment sizes from ions in solution, to silts and clays, also

cobbles, but normally not boulders unless peak flooding occurs.

• Cliffs may flank the river at a distance. Floodplain exists with grassy areas beside the

river.

• Meanders may be present though they will not be as curvy
• Erosion is present though deposition of sediments also occurs.
• river has a greater discharge than the youthful river. The river is capable of carrying more

a greater volume of sediment.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Floodplain are relatively flat area that borders a stream, which is periodically inundated with water during

high flow periods. The resulting decrease in velocity causes sediment carried by the stream, such as gravel, sand, silt, and clay, to deposit as alluvium on the floodplain. Large particles are deposited first, and much of this material is laid down alongside both banks.

Bluff a relatively steep slope at the outer edge of a floodplain, marking the outer limit of lateral erosion and

undercutting.

Natural levee is a narrow ridge of alluvium deposited at the side of the channel. During high discharge

periods when the stream floods, coarse sediment settles out near the stream channel and grades to finer material further away.

Back swamps located some distance away from the stream channel on the floodplain. When water spills

• ver onto the floodplain, the heaviest material drops out first and finest material is carried a greater
• distance. The fine-grained alluvium holds much water and drains rather slowly creating wetland areas. >

Stream terraces are elevated portions of a floodplain created when the stream down cuts and creates a

new floodplain at a lower elevation. Paired terraces occur at same elevations on opposite valley sides; produced by intermittent down cutting with changes in discharge, load or base level.

Old Age River

• river flows down a very shallow gradient
• Channel is wider than its depth with a very broad and U-shape due to extensive lateral erosion.
• Velocity is quite slow
• Small sediments are suspended in the slow-moving water giving the river a "muddy" appearance.

Dissolved salts and ions are carried in solution.

• The general landscape surrounding the river is flatter and less steeply sloped.
• floodplain is often marshy and swampy due to flooding of the river valley.
• S-shaped" Meanders are abundant and prominent features of an older river.
• Oxbow Lake sexist within the floodplain. Meanders were cut off from the main stream due to extensive

erosion and deposition.

• Natural Levees, ridges formed by successive floods that deposit sediment over time, flank the outside

meander curves.

• Point bars are areas of deposition on the inside curves of a meander.
• The discharge is quite large as it is fed by many smaller tributaries join the main river at various locations
• Erosion is present on the outside curves of meanders while deposition of sediments occurs on the inside

curves.

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Straight stream channels are rare. Where they do occur, the channel is usually controlled by a linear zone of weakness in the underlying rock, like a fault or joint system. Even in straight channel segments water flows in a sinuous fashion, with the deepest part of the channel changing from near one bank to near the other. Velocity is highest in the zone overlying the deepest part of the stream. In these areas, sediment is transported readily resulting in pools. Where the velocity of the stream is low, sediment is deposited to form

• bars. The bank closest to the zone of highest velocity is usually eroded and results in a cutbank.

Source courtesy: videoblocks.com

Matured river

Source courtesy: coolgrography.co.uk

• Prof. R. Nagarajan, CSRE , IIT Bombay

Braided Channels - In streams having highly variable discharge and easily eroded banks, sediment gets deposited to form bars and islands that are exposed during periods of low discharge. In such a stream the water flows in a braided pattern around the islands and bars, dividing and reuniting as it flows downstream. Such a channel is termed a braided channel. During periods of high discharge, the entire stream channel may contain water and the islands are covered to become submerged bars. During such high discharge, some of the islands could erode, but the sediment would be re-deposited as the discharge decreases, forming new islands or submerged bars. Islands may become resistant to erosion if they become inhabited by vegetation

Source courtesy: tulane.edu

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Meandering Channels - Because of the velocity structure of a stream, and especially in streams flowing over low gradients with easily eroded banks, straight channels will eventually erode into meandering channels. Erosion will take place on the outer parts of the meander bends where the velocity of the stream is highest. Sediment deposition will occur along the inner meander bends where the velocity is low. Such deposition of sediment results in exposed bars, called point bars. Because meandering streams are continually eroding on the

• uter meander bends and depositing sediment along the inner

meander bends, meandering stream channels tend to migrate back and forth across their flood plain.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Terraces are exposed former floodplain deposits that result when the stream begins down cutting into its flood plain (this is usually caused by regional uplift or by lowering the regional base level, such as a drop in sea level). Alluvial Fans - When a steep mountain stream enters a flat valley, there is a sudden decrease in gradient and velocity. Sediment transported in the stream will suddenly become deposited along the valley walls in an alluvial fan. As the velocity of the mountain stream slows it becomes choked with sediment and breaks up into numerous distributry channels.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Deltas - When a stream enters lake or ocean, again there is a sudden decrease in velocity and the stream deposits its sediment in a deposit called a delta. Deltas build outward from the coastline, but will only survive if the ocean currents are not strong enough to remove the sediment. As the velocity of a stream decreases on entering the delta, the stream becomes choked with sediment and conditions become favorable to those of a braided stream channel, but instead of braiding, the stream breaks into many smaller streams called distributary streams. Floodplains and Levees - As a stream overtops its banks during a flood, the velocity of the flood will first be high, but will suddenly decrease as the water flows out over the gentle gradient of the floodplain. Because of the sudden decrease in velocity, the coarser grained suspended sediment will be deposited along the riverbank,ventually building up a natural levee. Source courtesy: riverrestoration.wikispace.com

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Source courtesy: riverrestoration.wikispace.com

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Delta is a landform at the mouth of a river produced by the sudden dissipation of stream’s

velocity and the resulting deposition of the stream’s load. Distributaries: branching stream channel that crosses a delta. The following conditions are needed:- large sediment load, low velocity and loads must be deposited faster than it can be removed by the action of tides &

• currents. The shape of a delta depends on the rate of sediment supply, wave action and coastal

currents reworking the deposited sediment, and the rate at which the alluvial deposits subside.

Arcuate Delta are fan or inverted cone-shaped delta. In areas of significant wave activity

sediment will be redistributed laterally along the delta front to form a smooth arcuate shoreline with many sand bars, beach ridges and/or barrier islands. Where delta formation is river-dominated and less subject to tidal or wave action, a delta may take on a multi-lobed shape which resembles a bird’s foot. Tend to have one or a very few major distributaries near their mouths.

Cuspate Delta - tooth-shaped delta formed by a river that usually has one distributaries'

emptying into a flat coastline with wave action hitting it head-on. This tends to push the sediment back on both sides of the mouth.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Estuarine Delta - Developed when a river that

empties into a long, narrow estuary that eventually becomes filled with sediment inside the

• coastline. Mountain streams carrying a heavy

stream load loses their kinetic energy as they flow

• ut on to the flat plain depositing alluvium.

Alluvial fans are quite common in arid regions

where water is lost to evaporation and infiltration into coarse surface material when the stream exits the mountain front, forms when several individual alluvial fans merge into one broadly sloping surface

Source courtesy: geocaching.com

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

• 1. Mississippi delta is dominated by fluvial
• processes. The abandoned distributary ceases

to grow and is eroded back by wave action. Abandoned river channels and inactive subdeltas have developed on each side of the present river.

• 2. Nile delta is dominated by wave action

which produces an arcuate delta front.

• 3. Mekong delta is dominated by tidal forces

which produce wide distributary channels.

• 4. Niger delta has formed where stream

deposition, wave action, and tidal forces are about equal. An arcuate delta front and wide distributary channels are thus produced.

Source courtesy: explanet.info

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Lena river flowing into arctic Ocean. Lena delta refugee for wild life (source courtesy: pinterest.com)

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : River basin management

Major drainage basins of the world

Ocean basins - About 48.7% of the world's land drains to the Atlantic Ocean. In North America, surface water drains to the Atlantic via the Saint Lawrence River and Great Lakes basins, the Eastern Seaboard of the United States, the Canadian Maritimes, and most of Newfoundland and Labrador. Nearly all of South America east of the Andes also drains to the Atlantic, as does most of Western and Central Europe and the greatest portion of western Sub-Saharan Africa, as well as Western Sahara and part of Morocco. The two major mediterranean seas of the world also flow to the Atlantic Largest river basins - The five largest river basins (by area), from largest to smallest, are the basins of the Amazon, the Río de la Plata, the Congo, the Nile, and the Mississippi. The three rivers that drain the most water, from most to least, are the Amazon, Ganga, and Congo rivers. Endorheic drainage basins - are inland basins that do not drain to an ocean. Around 18%

• f all land drains to endorheic lakes or seas or sinks.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Source courtesy: grida.no

• India has 2% of world’s land, 4% of freshwater, 16% of population, and 10% of its cattle.
• Geographical area = 329 Mha of which 47% (142 Mha) is cultivated, 23% forested, 7%

under non-agri use, 23% waste.

• Out of cultivated area, 37% is irrigated which produces 55% food; 63% is rain-fed

producing 45% of 200 M t of food. India’s water Requirement in 2050 (Km3 = BCM)

• For growing food and feed at 420 to 500 million tonnes = 628 to 807 BCM
• Drinking water plus domestic and municipal use for rural population at 150 lpcd and for

urban population at 220 lpcd = 90 to 110 BCM

• Hydropower and other energy generation = 63 to 70 BCM
• Industrial use = 81 to 103 BCM ; Navigational use = 15 BCM
• Loss of water by evaporation from reservoirs = 76 BCM ; Environment and ecology = 20

BCM

Basin Area (sq km) Indus (Up to border) 321289 Ganga 861452 Brahmaputra 194413 Barak and others 41723 Godavari 312812 Krishna 258948 Cauvery 81155 Pennar 55213 East flowing rivers between Mahanadi and Pennar 86643 East flowing rivers between Pennar and Kanyakumari 100139 Mahanadi 141589 Brahmani and Baitarni 51822 Subernarekha 29196 Sabarmati 21674 Mahi 34842 West flowing rivers of Kutch and Saurashtra including Luni 321851 Narmada 98796 Tapi 65145 West flowing rivers from Tapi to Tadri 55940 West flowing rivers from Tadri to Kanyakumari 56177 Area of inland drainage in Rajasthan Minor rivers draining into Myanmar & Bangladesh 36202

Classification of rivers

Catchment area size

River basins are grouped, based on the size of their catchment areas (CA).

• 1. Major river basin Catchment area > 20,000 Sq.km
• 2. Medium Catchment area <20,000 >2000Sq.km
• 3. Minor (coastal area) <2000 sq.km
• 4. Desert rivers Flow is uncertain & most of them are lost in desert

Based on topography

• Himalayan Rivers flow throughout the year, are prone to flooding.
• Deccan/Peninsular Rivers include the Narmada and Tapi rivers that flow westwards into the

Arabian Sea, and the Brahmani, Mahanadi, Godavari, Krishna, Pennar & Cauvery that fall into the Bay of Bengal.

• Coastal Rivers are comparatively small in size and numerous in number, with nearly 600 flowing
• n the west coast itself.
• Inland Drainage Basin are centered in western Rajasthan, parts of Kutch in Gujarat and mostly

disappear before they reach the sea as the rainfall here is scarce. Some of them drain into salt lakes or simply get lost in the vast desert sands.

• Island Rivers Rivers of our islands: A&N islands & Lakshadip group of islands

• Himalayan Rivers Water: 300 utilizable, 1200 BCM available.
• Himalayan large dams presently store 80 BCM. New dams under consideration could

store 90 BCM.

• Peninsular Rivers Water: 400 utilizable, 700 BCM available.
• Peninsular large dams presently store 160 BCM.

New dams under consideration could store 45 BCM.

• Large dams presently store 240 BCM. New dams under consideration could store 135

BCM.

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Aggravates

Long-term shortage of water Floods Dependence on sophisticated technology for development Unsustainable development of fresh waters Mismanagement of irrigation schemes Conflicts arising from depletion of renewable resources Inadequate integrated freshwater management Water-related hazards and dangers Desiccation of rivers Conflicting uses of water

Aggravated by

Unethical practice of hydrology Loss of water to industrial uses Lack of international accord on water use Ignorance of ecoregions

Broader

Lack of international cooperation

Narrower

Water deprivation of downstream locations Environmentally destructive redirection of water flows

Source courtesy: pinterest.com

Source courtesy: Sarojbala.blogspot.com

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 624 : Water Resource and River basin management

Thank you