Slope Processes and Landform Development, a Geomorphological: Case Study of Idanre Area of Ondo State
Chapter One
OBJECTIVE:
The basic aim and objective of the present study are- ( a) To successfully use the computer-aided geographical data processing
in understanding the geomorphic characteristics and processes actively involved in changing the landscape of Idanre area and its vicinity;
( b) To understand the implications arising out of the drainage system and its analysis;
( c) To study the average slope, Relief ( Absolute, Relative) , drainage density, dissection analysis and land forms. etc of the study area.
CHAPTER TWO
LITERATURE REVIEW
To plan for the best use of land, it is essential to understand the characteristics of the area. Thus, there exists a close relationship between geomorphology and land use planning. In the light of the above relationship the present study – “Geomorphological Characteristics: A Case Study of Idanre area and its Vicinity, Ri-Bhoi district, Ondo“, has been undertaken.
LITERATURE REVIEW:
Several books have been consulted in this dissertation. The concept of understanding geomorphology was based on many geomorphology texts. Bloom’ s Geomorphology: A Systematic Analysis of Late Cenoz oic Landforms ( 1991) and Thornbury’ s Principles of Geomorphology ( 1969) form the basis of understanding of geomorphology. For understanding the physical framework and the geology of a region as a whole a few books have been consulted. These are Ondo: Land and People ( Gopalakrishnan, 2001) , Ondo, the Land and Forest: A Remote Sensing Based Study ( Sarma, 2003) and Geography of North-East Nigeria ( Taher and Ahmed, 2007) . The landforms and drainage system, as well as the geological structure of the basin area, are well understood from the PhD thesis “Geomorphology and Land-use planning of Idanre Basin, Ondo ( Syiemlieh, 1998) “. Besides these, numerous GIS books have been consulted. These are, Introduction to Geographic Information Systems ( Kang-Tsung Cheng, 2008) , GIS Solutions in Natural Resource Management, Balancing the Technical Political Equation ( Morain, 1999) , GIS: Fundamentals, Application and Implementation ( Elangovan, 2006) . All these books have their immense importance which had helped me in complementing the dissertation work successfully.
The change in the river course is a natural process that had occurred since the dawn of human civiliz ation. Such changes are brought by various forces acting on the earth’ s surface, disrupting and changing the courses of water flow in the stream channel. These forces are irregular, dynamic and unpredictable till today. Therefore the changes brought by these forces have caused immense instability in the river channel, whereby different landforms and subductions z ones are created changing the morphology of the river from time to time. In the following lines, relevant literature has been reviewed to understand the research directions in the area of morphological studies of rivers.
J ohnson ( 1932) suggests that early youth end when lakes are eliminated and the middle youth ends when falls and rapids are eliminated. Late youth ends and early maturity starts when the rate of down cutting decreases and the rate of lateral erosion increase; establishment of grade also marks the passage from youth to maturity. According to J ohnson, early maturity ends and late maturity begins when the valley width is equal to the width of the belt covered by the meanders of the stream. Such a process in the channel tends to bring changes in the morphology of a river.
Grant ( 1950) and Campbell ( 1945) observed that the man induce forces and the destruction of the natural vegetation on steep slopes on extreme humid areas of New Z ealand have changed the morphology of the river over time. Stable, narrow and sinuous rivers have changed to wide. Straight channels as a result of an influx of coarse sediments into the channels and aggradation and an increase in flood peaks have occurred.
According to Miller ( 1958) , he found that when comparably-siz ed rivers join, the stream gradient below the junction averages one-third of the sum of the two tributary gradients and that the downstream channel width is two-thirds of the sum of the tributary widths. Channel width measurements within a single stream-link suggest the absence of any significant linear trend. The width of the valley bottom usually increases downstream but the effects of tributary inputs may not be detectable because the valley width is strongly controlled by variations in bedrock and reflects palaeo-hydrological conditions.
Hack in ( 1960) , observed that as the erosion cycle proceeds, the morphology of the streams changes and passes through the three stages of development in the earth’ s surface. Although the stage reached by the stream usually corresponds to that of the surrounding topography, this is not necessarily the case. Usually, the stream is less youthful near its mouth than in the vicinity of its headwater.
According to Leopold, et al ( 1964) , he viewed that the shape of the cross-section of a river channel at any location as a function of the flow, the quantity and character of the sediment movement through the section, and the character or composition of the materials making up the bed and banks of the channel. Because the flow exerts shear stress upon the bed and the banks, one ‘ adjusted’ or stable form which the channel can assume is one in which the shear stress at every point on the perimeter of the channel is just balanced by the resisting stress of the bed or banks at each point. Thus, here the shear stress is given importance.
Morisawa ( 1968) described the field of study of stream morphology. According to her, the overall geometry of a stream channel is controlled by the independent variables of discharge and load, i.e. the climate and geology of the watershed. Thus, according to Morisawa, the channel characters of streams are dictated by the climatic and geological conditions in other areas.
According to Petts and Foster ( 1985) , in their book entitled ‘ Rivers and landscapes ‘ the river channel presents a three-dimensional form- defined by its slope, cross-section and pattern which must be considered within the context of the drainage basin because it is the mutual adjustment of the hill slopes, drainage network and channel morphology that maintains continuity of transfer of water and sediments.
CHAPTER- THREE
GENERAL CHARACTER OF THE STUDY AREA
PHYSIOGRAPHY:
Physiography studies the physical characteristics of the region where it is located. The study of this physical characteristic includes the geological history of the Ondo plateau and particularly the study area. The best way to understand the geological background of the watershed is through the understanding of the geological history of the Ondo plateau and the whole region of North-East Nigeria. As a whole, North-East Nigeria is geologically a very complex region. The
Ondo Plateau as a part of the region has also a long story of erosion, sedimentation, folding, diastrophism, intrusions, and movement of land and sea emissions. North-East Nigeria represents the dynamic frontal part of the Nigerian plate and in the opposite direction; there is a presence of relatively stable central ( Chinese) plate. Between these two plates there lay the orogenically active bed of Tethys Geosynclines. Their collision has greatly complicated the crustal structure of the whole region and experiences the high degree effects. The earthquakes in this z one are primarily due to plate tectonics. Based on intensities of the earthquakes recorded on the Modified Mercalli Intensity Scale, the Nigerian Standards Institute grouped the whole North-East Nigeria into Seismic Z one V. This indicates that the region is seismologically active. These forces generate a huge amount of energy in the interior of the earth` s crust which the region has to release from time to time in the form of earthquakes. Therefore, all these activities reflect a weak crustal construction in this region. The accumulation of sedimentary deposits and organic remains due to the plate margin convergence has resulted in the formation of low-density continental crust in the existing basins. These basins have been formed parallel to the margins of the pre-existing lines of weakness, which permits the formation of thick and thin continental crust. Due to the compressional forces, the thinner crust fractured and collapsed, while the thick crust was too thick to crumble, so it was uplifted. Numerous features are produced due to these uplifts and subsidence of landmasses such as the flat-topped hills, the gorges on the south, typical horst, etc. The region also has a large number of thrusts and faults.
CHAPTER FOUR
GEOLOGICAL SETTINGS OF ONDO:
The Ondo plateau is sandwiched between the Himalayan and Burmese elevator movements. “The geological formation of the Ondo plateau is similar to the rock formations of the peninsular plateau and regarded as the detached north-eastern extension of Peninsular Nigeria, cut off by the intervening spread of the Ganges and Brahmaputra alluvium”. This gap is normally termed as the Malda Gap or Raj Mahal – Garo Gap ( Between Chhota Nagpur or Raj Mahal hills and Shillong plateau) .
Broadly, the unique Ondo plateau can be divided into the existing hills, the Garo, Khasi and J aintia Hills ( Table no. 2.l) along with their outline formed by the ranges of Assam.
CHAPTER FIVE
SUMMARY AND CONCLUSION
The traditional geomorphology has been excessively descriptive. In the past, much of the emphasis has been given in placing landforms into some evolutionary model, both at the local and regional level. The field was primarily concerned with the historical interpretation. The use of quantitative techniques has shifted the discipline to studies with more practical value. Now the uses of computer system and GIS techniques have changed the traditional geomorphology into a more advanced and useful one.
The study area is geographically located between the latitude 25048′ 19” to 25055′ 22” North and 91048’ 19” to 91056’ 02” East longitude lies in the maximum intensity z one earthquake. The application of GIS techniques to the study of the geomorphology of Idanre watershed revealed that the area has an elevation of 306 to 1013 meters from sea level. The distribution of area at a different elevation ( fig. 4.1) shows the relationship between the area and elevation. It indicates that 360- 450 meters elevation covering 12% of the area is a flood plain, 450-750 covering almost 80% of the watershed is flat-topped hills which are suitable for the development of human settlements and sedentary agriculture, the rest 8% of the area is characteriz ed as undulating hillocks. The area is composed of gneiss rock which is susceptible to weathering.
Idanre is a tributary of Umran River:
The Idanre stream flowing in a south-westerly direction is a perennial stream having numerous tributaries all along its course. It flows through an area dominated by granite rock formations. The Idanre stream has been greatly affected by both exogenic and endogenetic forces from over some time. Being located in an active tectonic belt, the area is not stable and keeps on changing from time to time. The processes operating in the area greatly affects the morphology of the stream where certain changes have been observed in the different characteristics of the stream like the channel depth, width, pattern, sediment and water discharge. In a place where the runoff coefficient is exceptionally high, there is every possibility of unexpected changes to take place ( Singh et.al. 2010) .
The channel morphology of the stream varies drastically over relatively short distances. Along its initial course, the Idanre stream is found to be highly diversified. Rapid changes in the stream characteristics ( rapids, potholes and exposed bed-rock) are observed. The field study was undertaken during the dry early spring season; hence, the water level of the stream was at its lowest. Numerous dry water channels were seen all along the stream length. Human intervention was noticed to some extent along the stream.
The streams are perennial and form the dendritic drainage pattern. The rivers in this region do not form any major waterfalls and deep gorges due to moderately gentle gradient of the slopes. The Watershed has 644 streams, out of which 501 streams are of 1st order, 113 streams are 2nd order, 20 streams are of 3rd order, and 9 streams are in 4th order and 1 stream in 5 orders, respectively. The valleys which cover 18% of the area with elevation ranging from 500-640 meters are more dissected than the areas having more than 720 meters of height. The stream frequency is very less in the hilly area which covers 30% of the watershed. Between the elevations 640-720 meters, the drainage density is 2-3Sq. Km. The bifurcation ratio of this elevation ( 52% of the area) is 2.86-3.5. The bifurcation ratio of the streams ranging from 2.0-5.7 indicates that the region has the hilly topography, streams are guided by the lineaments and the presence of lithologic constraints acts as barriers to the flowing water which causes flood during the monsoon season ( J un-September) . The bifurcation ratio in the 1st to 2nd stream orders is 4.43, 2nd to 3rd stream orders is 5.56, to stream orders is 2.22 and 4th to 5th stream orders is 9. This is very relevant for explanation. Bifurcation ratio of 9 indicates a very strong structural control in the area. It is possibly an area resulting from very strong movements in the past that have left scars on the land and eroded vigorously by the stream and also suggests that the areas with the maximum number of streams are more dissected and has a high drainage density and water discharge rate.
RELATION OF DRAINAGE WITH LINEAMENT:
In the basin, there are a large number of lineaments. The major drainage lines follow these lineaments which run for long distances in different directions. Comparing with the geological map, the major drainage lines are controlled by the lineaments. It has been specially pointed out that the lineaments in the gneissic terrain probably represent the master joints.
Drainage and lineament characteristics of a watershed provide important clues about the hydrogeology of the area. Information about the above characteristics derived from satellite imageries aided by field verifications and subsequently analyz ed in Geographical Information System ( GIS) environment can provide a composite map and which can be used for adopting a suitable strategy for managing watersheds in a better way.
Based on the above concept, drainage, lineament and hydrogeomorphic study of the upper catchment area of Idanre basin, Idanre. Granitic lithology and uneven topography indicate that the surface run-off is high and infiltration is low and therefore groundwater recharge is inadequate in the area. Integrating different types of thematic layers like drainage, lineament in a GIS environment; it has been possible to understand that the drainage system of Idanre basin is directly related to the lineament alignments of the area. In the fig no. 3.6 we can easily found that the streams are mostly following the major and minor lineaments of the area. Approximately 80% of streams are following the lineaments after originating from the nearest highland.
Therefore, GIS is a very useful technique because it allows for the quantitative evaluation of the relationship between the Geomorphological features and process of the study area and its Geology. Further, it can be related to the land use pattern, engineering works, etc. This GIS produced maps can also apply for the development, planning and decision making of a particular area.
REFERENCES
-
- Dikshit, R.D. ( 1997) : Geographical Thought: A Contextual History of Ideas, Prentice-Hall of Nigeria Private Limited, New Delhi, pp. 9-17.
- Bloom. Arthur L ( 1991) : Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Prentice-Hall of Nigeria Private Limited, USA, pp. 1-2.
- Strahler, A.N., ( 1968) : The Earth Sciences, Harper International, New York, P.452.
- Thombury, William D ( 2006) : Principles of Geomorphology, New Age International ( P) Limited Publishers, USA, pp.l-12
- Singh Savindra. ( 2009) : Geomorphology: Channel Morphology, Prayag Pustak Publishers. Allahabad.
- Devi, H.1. ( 2000) : River Basin Morphology, New Delhi, Rajesh Publication.
- Taher, M and P. Ahmed ( 2007) : Geography of North-East Nigeria, Mani Mani Prakash, Guwahati, pp. 22-24.
- Elangovan, K. ( 2006) : GIS: Fundamentals. Application and Implementation, New Delhi Publishing Agency, New Delhi, pp. 1-3, 25-31
- Leopold, L. B., Wolman, M. G. and Miller, J . P. ( 1964) : Fluvial processes in Geomorphology, New Delhi, S. Chand and Company Ltd,
