The Sinuosity Index

Sinuosity index

The shape and pattern of streams can be easily identified and classified from its planform nature through the visual analysis. Though the planfrom nature of the river can be inferred from the topographical sheets or satellite images, it lacks the scientific background to compare with the standard classification proposed by Schumm (1963) and Rosgen (1994). In order to classify and characterize the shape of the stream, sinuosity index measured from the segment of stream under consideration were used (Schumm, 1963; Leopold and Wolman, 2013). The sinuosity index (SI) is a dimensionless parameter, which can be calculated by ratioing the length of stream segments measured through the streamline to the air (straight line) distance

From the selected segments, different channel reaches are used to calculate the sinuosity indexes and the values of the index are varying from 1.3 to a maximum of 2.8 indicating the transition of stream segments from normal sinuous nature to irregular meander. In the lowland segment analysed, the sinuosity index varies from 1.3 (sinuous) to 2 (meandering). A similar trend was also noted in the midland segment with the sinuosity index, ranging between 1.4 (sinuous) to 1.9 (meandering). At the same time, it was noted that the maximum sinuosity index was shown by the highland segment of the river, which varies from 1.3 (sinuous) to 2.8 (meandering with channel bars). The high value of sinuosity indexes represents a change in the planform pattern of river in this region. The characteristic stream pattern shown by the whole river and the segments analyzed vary from irregular meander to tortuous meander. It was noted that the tortuous meandering nature of the river was found in the midland and highland segments and indicating differential characteristics of the stream bed, which might have been influenced by the geological process than

Cross profiles are capable of expressing the variation in stream bed characteristics and stream valleys by showing the trade-off between symmetric to asymmetric and paired to unpaired characteristics of the river valleys and also showing different types of valleys such as ‘V’, ‘U’ and open valleys. In order to understand the cross-profile characteristics of the river channel, three cross profiles were generated from the lower, middle and upper reaches and are shown in figure 8. In the lower segment of the river Akah, among the three cross profiles generated the middle section shown smooth, uniform ‘U” shaped valley whereas all others shown variable bottom characteristics with unpaired terraces. At the same time the cross profiles of the middle reach segment shown more or less similar characteristics with broad open valleys. Among this the profile segment at the highest elevation shown a wide open valley with left side inclination. But while considering the cross sections of the river segments in the upper catchment region, it is shown open ‘V’ shaped valley to broad “U’ shaped valleys. This indicates changes in the channel pattern in different segments of the river which was reflected as misfit channel cross profile