7 Drainage mapping and Morphometric analysis

Objectives

To understand drainage mapping and morphometric analysis
Method of calculating morphometric parameters

Keywords

Drainage mapping, morphometric analysis, drainage basin, linear aspect, areal aspect, relief aspect.

Introduction

This chapter describes the drainage mapping and their morphometric analysis. Drainage is a system of draining water, passage of water over and through the land surface, ultimately towards the sea. The dictionary meaning drainage is the process of removing the gravitational water from soil, using artificial or natural conditions, such that freely moving water can drain, under gravity, through or off soil (Allaby, 2008). The area that collectswater into the drainage system with single outlet is known as drainage basin. It is an area that gathers water from precipitation and delivers it to a large stream, a lake, or ocean which is limited by a drainage divide and occupied by drainage network.The drainage basin consists of different types of pattern such as dendritic, rectangular, trellis and many more. The drainage system can be sequent or insequent. Sequent drainage system consists of consequent, subsequent, obsequent and resequent, according to the geological structure of the surface.The insequent drainage system has antecedent and superimposed type, where there is a lack of adjustment to geological structure.The term morphometry is used in several disciplines to mean the measurement and analysis of forms characteristics (Gardiner). In 1934 Emmanuel De Martonne defined morphometry in his book ‘Trait de Geographic Physique’, as the numerical systematization of the forms of the land relief as it can be interpreted from a topographic map.Basically, morphometry is the measurement and mathematical analysis of the configuration of the earth’s surface, shape and dimensions of the landform (Clarke, 1966). It provides quantitative description of the basin geometry to understand initial slope or inequalities in the rock hardness, structural controls, recent diastrophism, geological and geomorphic history of drainage basin (Strahler, 1964). According to Horton (1945), drainagemorphometry is a calculation of arange of dimensionless drainage-network relationships, based on a system of stream ordering, i.e. the numerical ranking of channel segments within a channel network. Drainage basin morphometry is measurement of the surface form of a drainage basin, and of the arrangement and organization of the associated river network. Properties such as area, shape, gradient, and relief are important elements of form, while the stream network is investigated through a study of its components and of the ways in which they are related. It enables us to understand the relationship among different aspects of the drainage pattern of the basin, to make a comparative evaluation of different drainage basins developed in various geologic and climatic regimes (Nag et al., 2003).

Need

The mapping of drainage and their basin is most important for the development of land and water resources on a sustained basis and with constant increase in productivity is necessary for the sustainable development. These developments depend on the prudent use of land and water resources, their conservation and development. In the face of the enormity of degradation problems and constraints of resources, a scientific approach to land and water resources development and management calls for a clear identification of critical areas for treatment. Drainage basin is an ideal geo-physical unit needing multi-disciplinary approach to the land and water resource management for ensuring benefit on sustained basis. The characteristics of drainage basin help to understand and model various natural processes occurring in the watershed and these watersheds or hydrologic units are considered more efficient and appropriate for necessary survey and investigations for the assessment of these resources and subsequent planning and implementation of various development programmes like soil and water conservation, command area development, erosion control in catchments, dry land/rainfed farming, reclamation of ravine lands, etc. The hydrologic units are equally important for the development of water resources through major, medium and minor storage projects as well as farm level water harvesting structures. So the watershed approach is more rational because land and water resources have optimum interaction and synergetic effect when developed on the watershed basis.

Since the work cannot be started at the same time in all the watersheds due to manpower and resources constraints, a priority list is to be prepared. In this way morphometric analysis of the drainage basin helps us to prioritize the watershed on the basis of their characteristics. The prioritization of an areas helps in addressing the conservations efforts to secure maximum benefit.

The science of morphometry is concerned with the quantitative measurement and generalization of land surface geometry. The drainage basin and channel morphology are related to the geologic, climatic and hydrologic character of the basin, then it is necessary to describe the features quantitatively in order to investigate these relationships. There are three aspect of drainage basin morphometry such as linear, areal and relief aspects of the watershed characteristics.

Linear aspects

The linear aspect of basin characteristics includes number of streams, stream order, basin parameter, basin length, bifurcation ratio, wandering ratio, overland flow and lengths of channels of all orders. Usefulness of ordering channel system lies on the hypothesis that basin size, channel dimension, and stream flows are proportional to the stream orders provided investigation is made for quite large number of watersheds. Two basins having different linear measures can be compared with respect to corresponding points in their geometry through use of dimensionless order numbers (Table 1).

Stream orders: There are various systems of ordering the stream that are available (Horton, 1945; Strahler, 1957 and Shreve, 1966), Strahler’s system, which has in fact slightly modified Horton’s stream ordering system, was followed because of its depend on the prudent use of land and water resources, their conservation and development. In the face of the enormity of degradation problems and constraints of resources, a scientific approach to land and water resources development and management calls for a clear identification of critical areas for treatment. Drainage basin is an ideal geo-physical unit needing multi-disciplinary approach to the land and water resource management for ensuring benefit on sustained basis. The characteristics of drainage basin help to understand and model various natural processes occurring in the watershed and these watersheds or hydrologic units are considered more efficient and appropriate for necessary survey and investigations for the assessment of these resources and subsequent planning and implementation of various development programmes like soil and water conservation, command area development, erosion control in catchments, dry land/rainfed farming, reclamation of ravine lands, etc. The hydrologic units are equally important for the development of water resources through major, medium and minor storage projects as well as farm level water harvesting structures. So the watershed approach is more rational because land and water resources have optimum interaction and synergetic effect when developed on the watershed basis.

Linear aspects

Figure 1:Stream order by different authors

Stream numbers: The number of streams is calculated in each watershed after assigning the stream order of each stream. The analysis of the study reveals that the number of stream decreases as the stream order increases. There is more first order stream than any other order and that the first order streams on the average are shorter and occupy smaller drainage basins. The stream discharge increases systematically with stream order and these relations indicate that the drainage network has developed in response to the erosive forces acting on the erodable materials that comprise the drainage basin.

Bifurcation ratio:Bifurcation ratio as an index of relief and dissections and it is computed by dividing the number of stream segments of a given order by the number of stream segments of the next higher order (Schumm, 1956). Lower bifurcation ratio values are the characteristics of structurally less disturbed watersheds without any distortion in drainage pattern (Figure 3). The bifurcation ratio between 3 and 5 indicates that geologic structures have not distorted the drainage pattern of the basin.

Figure 2: stream order of drainage basin

Figure 3: Mean bifurcation ratio

Exceeding value pronounced structural control encourages the development of elongate narrow drainage basin. Higher of bifurcation ratio indicates a high run-off, less infiltration and mature nature of topography, which is the result of variation in higher and lower order stream segments. These irregularities are dependent on geological and lithological development of drainage basin (Strahler, 1964). It was calculated by using the given formula;

Where, = Bifurcation ratio; = Total number of stream segments of order ‘u’; + 1 = number of segments of the next higher order

Stream lengths: The length of the various stream segments can be measured order wise and the total length as well as the mean length of each order can be computed. The mean length for the given order can obtained by dividing the total length of the total number of segments of the same order. The mean stream length of a channel is dimensional property and reveals the characteristics size of drainage network components and its contributing basin surfaces (Strahler, 1964). The mean length of stream is an increasing trend with increase in order.

Length of overland flow: Horton (1945) defined as the length of flow path, projected to the horizontal, of non-channel flow from a point on the drainage divide to a point on the adjacent stream channel. It is the length of overland flow of water before it joins a channel. It is reverse relationship between drainage density and overland flow. This factor relates inversely to the average slope of the channel and it quite synonymous with the length of sheet flow to a large degree. The average length of overland flow is approximate half the average distance between stream channels and is therefore approximately equal to half the reciprocal of drainage density.

The analysis reveals that the length of overland flow is varying between 0.10 and 2.26 in WS11 and WS2 respectively. The WS6 to WS13 has low (less then 0.5) overland flow, except WS9 where it is more than one (Figure 4). Horton noted that “length of overland flow is one of the most important dependent variables affected both the hydrologic and physiographic development of drainage basins”. It is calculated as;

Where, = Length of overland flow; D = Drainage density

Wandering ratio: The ratio between main stream length along the course to the straight line distance between the two extremes outlet and farthest point in the basin boundary. While this factor broadly indicates the amount of deviation of main stream from straight line path, it does not necessarily explain the meandering of the main stream. The wandering ratio in the watershed is varying between 1.09 and 1.89 in WS3 and WS4 respectively (Figure 5). The low wandering ratio shows the less time of run-off and vice versa. It is calculated as;

Where, Rw = Wandering ratio; Msl = Main stream length along the course; = Basin length

Figure 4: Length of overland flow

Figure 5: wandering ratio

Table 1: Linear aspect of Son-Karamnasa interfluve

Table 2: Number of stream and bifurcation ratio of the watersheds

Areal aspects

The areal aspect of the drainage basin includes the drainage area, drainage density, drainage texture, basin shape configuration, constant of channel maintenance (CCM) etc. (Table 7.3).

Drainage area: It represents the area enclosed within the boundary of the watershed divide. The watershed-wise analysis reveals that among thirteen watersheds, the WS12 has lowest drainage area i.e. 3,328.4 hectares and WS1 has the largest drainage area i.e. 191,209.1 hectares. The drainage area a probably the single most important characteristics for hydrologic design. It reflects the volume of water in the watershed that can be generated from rainfall and the length of the stream draining it.

Watershed shape factor:The watershed shape factor was defined as the ratio of the main stream length to the diameter of the circle having the same area as of watershed (Figure 6). The analysis reveals that the watershed shape factor is varying between 1.59 and 4.73 in WS12 and WS3 respectively. The lower value shows the higher run-off and circular in shape and the higher value shows low run-off and elongated shape of the watershed. It also reflects the drainage pattern of the study area. It is calculated as;

Sw = L / D

Where, Sw = Watershed shape factor; L = Main stream length; D = Diameter of the basin

Figure 6: watershed shape factor

Table 3: Areal aspect of Son-Karamnasa interfluve

Source: Generated by Author

Drainage density: It expresses the closeness of spacing of channels. It is defined as the ratio of total length of channels of all orders in the basin to the drainage area of the basin. It is affected by factors which control the characteristics length of the stream like resistance to weathering, permeability of rock formation, climate and vegetation etc. The low value of drainage density is observed in regions underlain by highly resistant permeable material with vegetative cover and low relief. High drainage density is observed in the regions of weak and impermeable subsurface material and sparse vegetation and mountain relief (Figure 7). The drainage density is calculated by using formula:

Whereas,D = Drainage density; Lu = Total stream length of all orders; A = Area of the basin in square kilometer

Stream frequency: Stream frequency is defined as the number of streams per unit area (Figure 8). There is close relationship between stream frequency and run-off. The higher stream frequency has more run-off and vice-versa.

Whereas, Fs = Stream frequency; Nu = Total number of streams of all orders; A = Area of the basin in square kilometer

Constant of channel maintenance (CCM): It is defined as the ratio between the area of a drainage basin and total lengths of all the channels expressed as square kilometre per kilometre. It is equal to the reciprocal of drainage density. This parameter indicates the number of square meters of watershed surface required to maintain one linear metre of channel. Constant of channel maintenance is inverse to the drainage density. The analysis reveals that the values of the constant of channel maintenance are varying between 0.21 and 4.51 in WS11 and WS2 respectively (Figure 9). It means that 0.21 and 4.51 square metre surface require maintaining 1 metre of the channel in WS11 and WS2 respectively. The higher value indicate that the channel capacity should be large enough to carry higher discharge resulting from the bigger drainage area.It is calculated as;

Whereas, C = Constant of channel maintenance; D = Drainage density

Drainage texture: It is the total number of stream segment of all orders per perimeter of that area (Horton, 1945). It is the coarseness or fineness of the dissection of the drainage network. The drainage texture of the watersheds is varying between 0.17 and 12.01 in WS9 and WS7 respectively (Figure 10). Smith (1950) has classified drainage density into five different texture i.e. very coarse (<2), coarse (2 – 4), moderate (4 – 6), fine (6 – 8), and very fine (> 8). According to Smith’s classification method, WS1, WS2, WS4, WS5 and WS9 has very coarse; WS3 and WS6 has coarse; WS4 has moderate; WS12, WS13 has fine; and WS7 and WS8 has very fine drainage texture. Horton recognized infiltration capacity as the single important factor, which influences drainage texture and considered the drainage texture to include drainage density and stream frequency. It is calculated as;

Whereas, Rt = Drainage texture; Nu = Total number of streams of all orders P = Perimeter in kilometer

Figure 7: drainage density

Figure 8: stream frequency

Figure 9: Constant of Channel Maintenance

Figure 10: drainage texture

Form factor: It is defined as the ratio of basin area, to the square of basin length (Horton, 1945). The value of form factor would always be less than 0.7854 (for a perfectly circular basin). In the study area it ranges between 0.04 and 0.69 in WS3 and WS12 respectively. The WS9 and WS3 has low; WS2, WS4, WS5, WS6, WS7, WS10 and WS13 has medium; and WS1, WS8, WS11 and WS12 has high form factor (Figure 11). The analysis also reveals that the smaller the value of form factor, more elongated will be the basin. The basins with high form factors have high peak flows of shorter duration, whereas, elongated sub-watershed with low form factors have lower peak flows of longer duration. Flood flows of such elongated basins are easier to manage, than those of the circular basin. The form factor is a dimensionless parameter and is computed as;

Whereas, Rf = Form factor; A = Area of the basin in square kilometer; Lb = Basin length

Circulatory ratio: Basin circularity ratio is defined as the ratio of the basin area to the area of a circle having circumference equal to the perimeter of the basin. It is influenced by the length and frequency of streams, geological structures, land use/cover, climate, relief and slope of the basin. The basin shape approaches to a circle, the circularity ratio approaches to 1. The circularity ratio in the study area is ranging between 0.12 and 0.74 in the WS1 and WS12 respectively (Figure 12). It is computed as the ratio of basin area to the area of a circle having same perimeter as of the basin. The higher circularity ratio also indicates the larger amount of flow and vice-versa. It is calculated as;

Whereas, Rc = Circulatory ratio; A = Area of the basin in square kilometer; P = Perimeter in kilometer

Figure 11: form factor

Figure 12: circulatory ratio

Elongation ratio: Schumm (1956) defined as the ratio between the diameter of a circle with the same area as the basin and basin length. The value of elongation ratio approaches to 1 as the shape of the basin approaches to circle. A circular basin is more efficient in run-off discharge than an elongated basin (Singh and Singh, 1997). The value of elongation ratio in the study area varies between 0.23 and 0.94 in the WS3 and WS12 respectively, associated with a wide variety of climate and geology (Figure 13). Values close to 1.0 are typical of regions of very low relief whereas that of 0.6 to 0.9 are associated with high relief and steep ground slope (Strahler, 1964). Higher value of elongation ratio indicates mature to old stage topography. Higher values of elongation ratio have circular shape. It is calculated as.

Elongation Ratio (Re) = 2√ (A/Pi) / Lb

Where, Re = Elongation ratio; A = Area of the basin in square kilometer; Pi = Pie value i.e. 3.14; Lb = Basin length

Figure 13: elongation ratio

Relief aspects

Basin relief:It is themaximum vertical distance from the stream mouth to the highest point on the divide. Basin relief has been defined in several ways. Schumm (1956) measured it along the longest dimension of the basin parallel to the principal drainage line whereas Strahler (1954, 1957) obtained it by determining the mean height of the entire watershed divide about the outlet. In the Son-Karamnasa interfluve basin relief is ranging between 38.44 metre and 593.96 metre in WS1 and WS7 respectively. WS1, WS2 and WS5 has low; WS9 to WS11 and WS12 has medium; and WS3, WS4,

WS6 to WS8 and WS13 has high basin relief (Figure 14). Relief is an indicative of the potential energy of a given watershed about a specified datum available to move water and sediment down slope. It is calculated as;

Maximum basin relief = He – Le

Where, He = Highest point in the basin; Le = Lowest point in the basin

Relief ratio: The ratio between the basin relief and the basin length is known as relief ratio. In a normal shaped basin the relief ratio is a dimensionless height – length ratio equal to the tangent of the angle formed by the intersection at the basin mouth of a horizontal plane passing through the highest point on the divide. The relief ratio in the watershed is varying between 0.03 and 1.75 in WS12 and WS2 respectively (Table 4). The WS1 and WS2 has highest; WS5 has medium; and others has low relief ratio (Figure 15). This parameter permits comparison of the relief of the two basins without regard to the scale of the toposheet. It measures the overall steepness of the watershed and can be related to its hydrologic characteristics. It is calculated as;

Relief ratio (Rh) = H / Lb

Where, Rh = Relief ratio; H = Total relief (relative relief) of the basin in kilometers; Lb = Basin length

Area elevation relation: Distribution of areas between contours in a drainage basin is of interest for comparing drainage basins and to understand the storage and flow characteristics of the basin. For the purpose an area distribution curve can be obtained by computer system itself in between contours. The mean elevation is determined as the weighted average of elevations between adjacent contours. In the Son-Karamnasa interfluve about 73.26 per cent area below 200 metre above mean sea level which is almost plain. The 26.74 per cent area is above 200 metre above mean sea level, which is very high slope (Figure 16).

Figure 14: basin relief

Figure 15: relief ratio

Table 4: Relief aspect of Son-Karamnasa interfluve

Source: Generated by researcher.

Figure 16: Area – Elevation of the Son – Karamnasa interfluve

Relative relief: It is defined as the ratio of the basin relief, to the length of the perimeter. Relative relief is an indicator of the general steepness of a basin from summit to mouth. The analysis reveals that the value is ranging between 0.16 and 10.97 in the WS1 and WS12 respectively (Figure 17). It has an advantage over the relief ratio in that is not dependent on the basin length. It is calculated by using the formula given by Melton (1957) as below:

Rr = 100H / 5280 P

Where,Rr = Relative relief; H = Basin relief,P = Perimeter.

Figure 17: Relative relief

Ruggedness number

It is the product of basin relief and the drainage density. It describes the quality of the slope steepness with the length.This is a dimensionless measure and combines slope and length characteristics into one expression. The areas of low relief but high drainage density are as ruggedly textured as areas of higher relief having less dissection. It is calculated by

?? = ?D

Whereas, Rn = Ruggedness number; H = Basin relief; D = Drainage Density.

Stream sinuosity index

it is a ratio between river channel length and length of river valley. It represents the degree of deviation of stream actual path from expected theoretical straight path. The value of index indicate the river course such as tortuous (index value 2.1), irregular (1.7), regular (1.5), transitional (1.2) and straight (1.0). The value also indicates the stages of basin development and landform evolution. It is calculated by the formula:

Whereas, SI = Stream sinuosity index; CL = Channel length; BL = Basin Length

Conclusion

The drainage basin and their morphometric parameters of different aspects like linear, areal and relief show the different characteristics of the watershed.These different characteristics can be used to interpret the geologic conditions responsible for and the pattern is controlled by, and in turn has an influence on, the hydrology of the drainage basin. Drainage patterns refer to spatial relationship among streams or rivers, which may be influenced in their erosion by inequalities of slope, soils, rock resistance, structure and geologic history of a region.

Linear parameters have a direct relationship with run-off and erodability. Higher the value more is the erodability.On the contrary, as the shape parameters have an inverse relation with run-off and erodability. Lower the value more the erodability. More the relief value higher the run-off and more erodability. Basically, remote sensing and GIS have has an efficient tool in drainage delineation and their morphometric analysis. These morphometric parameters can also be used for prioritization of the watershedsfor land and water resource development plan.

you can view video on Drainage mapping and Morphometric analysis

References

All India Soil and Land Use Survey, 1991. “Methodology of Priority Delineation Survey”. AIS & LUP Technical Bulletin 9, All India Soil and Land Use Survey, Ministry of Agriculture, New Delhi.
Bali, Y.P. and Karale, R.L., 1977. A Sediment Yield Index for Choosing Priority Basins. IAHS-AISH Publ. 222.
Biswas, S. et al., 1999. “Prioritisation of Subwatersheds Based on Morphometric Analysis for Drainage Basin: A Remote Sensing and GIS Approach”. Journal of the Indian Society of Remote Sensing, Volume 27(3), pp. 155-166.
Clarke, J.I., 1966. Morphometry from Maps, Essay in Geomorphology, Elsevier Publication Company, New York.
Dutta, D. et al., 1996. “Comparative Quantitative Analysis of Watershed Geomorphology and Land Characteristics for Priority Rating Using Remote Sensing and GIS”, Indo-US Symposium on Remote Sensing and its Application, IIT, Mumbai.
Dutta, D. et al., 2002. Watershed Characterization, Prioritisation, Development Planning and Monitoring – Remote Sensing Approach. Indian Space Research Organisation, Bangalore.
Horton, R.E., 1945. “Erosional Development of Streams and Their Drainage Basins. Hydrophysical Approach to Quantitative Morphology”. Bull. Geol. Soc. Am. Volume 56, pp. 275-370.
Melton, M.A., 1957. “An Analysis of Relations Among Element of Climate, Surface Properties and Geomorphology”. Project NR 389-042. Technical Report number 11, Columbia University, Department of Geology, NR Geography branch, New York.
Nag, S.K., 1998. “Morphometric Analysis Using Remote Sensing Techniques in the Chaka Sub-Basin, Purulia District, West Bengal”. Journal of the Indian Society of Remote Sensing, Volume 26(1 & 2), pp. 69-76.
Nag, S.K. et al., 2003. “Influence of Rock Types and Structures in the Development of Drainage Network in Hard Rock Area”. Journal of the Indian Society of Remote Sensing, Volume 31(1). pp. 25-35.
Schumm, S.A., 1956. “Evolution of Drainage Systems and Slopes in Bad Lands at Perth Amboy, New Jersey”. Bull. Geol. Soc. Am., Volume 67, pp. 597-646.
Shreve, R.L., 1966. “Statistical Law of Stream Numbers”. Jour. Geol., Volume 74, pp. 17-37.
Singh, S. and Singh, M.C., 1997. “Morphometric Analysis of Kanhar River Basin”.
National Geographical Journal of India, Volume 43(1), pp. 31-34.
Smith, K.G., 1950. “Standards for Grading Texture of Erosional Topography”. Am. Journal Science, Volume 248, pp. 655-668.
Strahler, A.N., 1954. “Statistical Analysis in Geomorphic Research”. Jour. Geol., Volume 62, pp. 1-25.
Strahler, A.N., 1957. “Quantitative Analysis of Watershed Geomorphology”. Trans. Am. Geophs. Union, Volume 38, pp. 913-920.
Strahler, A.N., 1964. “Quantitative Geomorphology of Drainage Basins and Channel Networks”. in Handbook of Applied hydrology, Ven Te Chow (ed.), McGraw Hill, New York, Section 4-11, pp. 4-39.
Wischmeier, W.H. and Smith, D.D., 1978. Predicting Rainfall Erosion Losses – Guide to Conservation Planning. United States Department of Agriculture, Agriculture Handbook No. 537. Washington, D.C.
Allaby, Michael. 2008. Dictionary of Earth Science. Third edition. Oxford University Press, New York.