The Hydrologic Cycle

Runoff

Channel Flow

Sheet Flow

RunoffOverland (Sheet) Flow

Drainage Basindrainage basin - the total land surface drained by a system of

streams leading to the same outflow.drainage system - the streams, tributaries, and other bodies of

water by which a region is drained.drainage divide - the boundary between adjacent drainage basins.

Stream Order

stream order - a classification of relative position of streams in achannel network, assigning each link an integer ordernumber determined by thepattern of confluences in thetributary network headward ofthe given link.

The concept of stream order, the first quantitative method of analysing drainage networks, was developed in the 1940s by American hydraulic engineer and hydrologist Robert Horton.

Streams are ranked hierarchically: headwater streams with no tributaries belong to the first, and lowest, order; two first-order streams unite to form a second-order stream; two second-order streams form a third-order stream, and so on.

Horton subsequently developed a number of laws of drainage network composition, which relate stream order and a number of associated indices, such as stream length and number.

Stream Order

The bifurcation ratio and drainage area.

Stream number is the number of streams in each order for a particular drainage basin; the number in each order decreases exponentially, or geometrically, with increasing stream order.

Stream length measures the average (or mean) length of a stream in each order, and is calculated by dividing the total length of all streams in a particular order by the number of streams in that order.

The stream length in each order increases exponentially with increasing stream order.

The bifurcation ratio is the ratio between the number of streams in one order and in the next. It is calculated by dividing the number of streams in the lower by the number in the higher of the two orders;

the bifurcation ratio in most networks is approximately constant, varying between 3 and 5.

Drainage area measures the average drainage area of streams in each order; it increases exponentially with increasing order.

 Order Number of Segments Bifurcation Ratio  1 10  2 3 3.33 3 1 3.00    

Drainage Density (Dd) = StreamLength / Basin Area

Stream System Components

Drainage Patterns

Dendritic

Radial

Rectangular

Trellis

Parallel

Drainage Patterns used to infer underlying geological/other controls

TYPE STRUCTURAL CONTROLDendritic: Lack of structural control; rock/sediment of uniform resistance Parallel : Closely spaced faults; steep topography; non-cohesive 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

In geomorphology, drainage systems, also known as river systems, are the patterns 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. Geomorphologists 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.

The number, size, and shape of the drainage basins found in an area vary and the larger the topographic map, the more information on the drainage basin is available.

Drainage PatternsDendritic

Dendritic drainage systems (from Greek δενδρίτης, dendrites, "of or pertaining to a tree") are the most common form of drainage system.

In a dendritic system, there are many contributing streams (analogous to the twigs of a tree), which are then joined together into the tributaries of the main river (the branches and the trunk of the tree, respectively).

They develop where the river channel follows the slope of the terrain.

Dendritic systems form in V-shaped valleys; as a result, the rock types must be impervious and non-porous.

Most of the rivers of the Indo-Gangetic Plains are of dendritic type.

Drainage PatternsRadial

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 patterns A good example of a radial drainage pattern is

provided by the rivers originating from the Amarkantak Mountain. Rivers like Narmada, Son and Mahanadi originating from Amarkantak Hills flow in different directions and are good examples of radial pattern. This pattern is also found in the Girnar Hills (Kathiwar, Gujarat), and Mikir Hills of Assam

Drainage PatternsRectangular

Rectangular drainage develops on rocks that are of approximately uniform resistance to erosion, but which have two directions of joining 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.

A typical example of this drainage pattern is found is the Vindhyan Mountains of India.

Drainage PatternsTrellis

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 angle, causing a trellis-like appearance of the drainage system.

Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America and in the north part of Trinidad

The old folded mountains of the Singhbhum (Chotanagpur Plateau) have drainage of trellis pattern.

Parallel drainage patternA parallel drainage system is a pattern of rivers caused by steep slopes with some relief.

Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction.

This system forms on uniformly sloping surfaces, for example, rivers flowing southeast from the Aberdare Mountains in Kenya.

Parallel drainage patterns form where there is a pronounced slope to the surface. A parallel pattern also develops in regions of parallel, elongate landforms like outcropping resistant rock bands.

Tributary streams tend to stretch out in a parallel-like fashion following the slope of the surface.

A parallel pattern sometimes indicates the presence of a major fault that cuts across an area of steeply folded bedrock.

All forms of transitions can occur between parallel, dendritic, and trellis patterns

The Stream Valley

Lecture 12III.D.4

Stream Valley DevelopmentEvolution

Lecture 12III.E.iii

Stream Valley DevelopmentBase Level

Lecture 12III.E.i

Stream Valley DevelopmentLateral Erosion

Lecture 12III.E.iii

Stream Valley DevelopmentEvolution – Headward Erosion

Lecture 12III.E.iii

Controls on Stream Function

Lecture 12IV.A

Velocity

Channel Properties

Gradient

Discharge

Controls on Stream FunctionVelocity

Lecture 12IV.A.i

Controls on Stream FunctionChannel Properties – Cross-Sectional Area

Lecture 12IV.A.ii.1

Controls on Stream FunctionStraight Channel

Lecture 12IV.A.ii

Controls on Stream FunctionMeandering Channel

Lecture 12IV.A.ii

Controls on Stream FunctionBraided Channel

Lecture 12IV.A.ii

Controls on Stream FunctionDischarge

Lecture 12IV.A.iv

discharge : volume of water flowing past a point in a given amount of time.

Erosion

Lecture 12IV.B

Sediment Transport

Lecture 12IV.C

capacity: the total volume of sediments a stream cancarry; a function of discharge

competence: the maximum size of sediment the stream can carry

Transport Modes

1Suspended load

2Bed load

3Dissolved load

Flood Plains

Lecture 12IV.D.iv

Meandering Streams and Point Bars

Lecture 12IV.D.iii

Meandering Streams and Point Bars

Lecture 12IV.D.iii

Meandering StreamsMigration

Lecture 12IV.D.iii

Lecture 12IV.D.iii

Meandering Streams and Oxbow Lakes

Flood PlainsNatural Levees

Lecture 12IV.D.iv

Natural levees

Bars

Lecture 12IV.D.i

Braided Streams

Lecture 12IV.D.ii

Deltas

Lecture 12IV.D.v

Deltas

Lecture 12IV.D.v

Alluvial Fans

Lecture 12IV.D.vi

Alluvial Fan (Death Valley, CA)