CONCEPT OF CHANNEL PLANFORMS CHANGES ON POTENTIAL RIVER FLOODING

ABSTRACT


INTRODUCTION
Rivers have been a focus of man's activities since his sojourn on earth.So important to humanity are the benefits derived from rivers, and so necessary is the protection against floods and other river disasters, that pursuit for knowledge of riverine systems has advanced in leaps and bounds.Their irrigational use has provided the basis for powerful bureaucratic territorial governments typified by those that flourish in the Wang Ho in China, the Tigris and Euphrates in Mesopotamia (the area of land covering today's Iraq mostly, but also part of modern-day Iran, Syria, Turkey and Kuwait), the Nile in Egypt, and the Ganges-Brahmaputra in India (Xiufang et al., 2013;Conniff et al., 2012).Rivers have formed political boundaries between and within nations, and their vicissitudes have frequently led to disputes, for example, the Nile water problems between Egypt and Sudan, and the Mekong Basin Disputes in Vietnam and Cambodia (Russell, 2010).
A group researcher observes that the behavior of rivers, their channel network and interfluves and the character of their associated sedimentary deposits are of interest to a variety of engineers, geologists and geographers as well as individuals losing their property, cornfield or pasture to an aggressive river (Lords et al., 2009).Economically, rivers provide routes of commerce; they are important in terms of the petroleum, uranium, gold and placer minerals obtained from their sedimentary deposits.Channel planform is the two-dimensional appearance of a river in map view or the channel pattern as seen from an airplane (Jagers, 2003).Some researchers suggest that channel patterns (planform) include straight, meandering and braided forms (Lords et al., 2009).Straight river segments, as described by Jagers are those that are seldom longer than 10 times their channel width (Jagers, 2003).The meanders are winding curves or bends in a river, resulting from both lateral erosion and depositional processes and while the braided segment as a system of channels, splitting and rejoining around islands (Jagers, 2003).
The impacts of river planform changes on cultural features; bridges, culverts, and socio-economic holdings; agriculture and other investments and how they relate to flooding have attracted the attention of many scholars who have made immerse contributions on the impact it has on flooding and socioeconomic activities within a catchment (Yearwood, 2010;Kondolf et al., 2002;Larsen and Greco, 2002).Adjustments in river planform are also known to have adversely affected the ecosystem (Lord et al., 2009;Petts and Amoros, 1996).Several studies have revealed that invertebrates, fish, riparian vegetation, and wildlife adjust to the channel form, hydrologic and sediment transport regimes following adjustment in river planform (Naiman et al., 1993;Hughes, 1997;Ward, 1999;Holburt, 1984;Tiegs and Pohl, 2005).Hence, this attest to the fact that having a firm understanding of the planform dynamics of river channels has important implications for maintaining biodiversity and minimizing flood damage.
diastrophism, and land use act as upstream controls.Sediments eroded from the drainage basin flow through the tributaries and the mainstream, the hydraulic geometry of the stream channels and their longitudinal profile are altered to cope with the additional load.Rivers dictate landscape evolution, exert controls on erosional processes, set boundary conditions for hillslope processes, and govern the height limits of mountain ranges.The materials eroded through hill slope processes and bedrock channel incision are eventually transported by alluvial channels and that while these activities take place the channel morphology is also governed by a number of drivers including tectonic processes, climate, and local lithology that influence the river system over a range of time scales (Garde, 2006;Selander, 2004;2015).
Floods are natural occurrences that have been considered as a tragedy in some parts of the world for instance in Nigeria, but they have presented great opportunities in others for instance in Egypt.Floods move large amounts of sand, silt and debris downstream onto adjacent land, and eventually deposit water and suspended sediment over vast areas.These sediments have helped replenish topsoil components particularly valuable to agricultural lands and in some places, it has gradually elevated the landmass above sea level (Abowei and Sikoki, 2005).The causes of riverine flooding in most developing countries (including Nigeria) have been attributed to factors such as prolonged rainfall and urbanization with an attendant increase in runoff, but little attention has been paid to river channel changes as they influence floods.Therefore, this study attempts to assess Changes in Channel Planform and flooding in River Kaduna, Kaduna State, Nigeria.

Related Work
Lateral abrasion, accretion and lateral channel migration are the most important geomorphological processes, which affect river stability.Understanding the dynamics of lateral abrasion, accretion and lateral channel migration of rivers is significant to practical issues such as predicting channel migration rates for engineering and planning purposes as well as soil and water management.Lovric and Tosic assessed the rate of lateral abrasion and accretion, as well as the rate of lateral channel migration of the Bosna River in Bosnia and Herzegovina using remote sensing and GIS (Lovric and Tosic, 2016).Their investigations revealed that the river's shape and position have changed significantly during the period of study, with less erosion on the left bank and more erosion on the right bank.Accretion was more on the left bank and less on the right bank.They were able to estimate the average lateral channel migration per year.
Fashae and Faniran is a work on the alluvial section Lower Ogun River in Nigeria.They examine the morphologic variables collected through field measurements which included cross-section, depth and width, velocity and other field data (Fashae and Faniran, 2015).Analysis of Variance and Pearson Product Moment Correlation respectively revealed that downstream morphological characteristics of the river vary distinctively at each cross-section with bed slope as the most significantly varied among all other morphologic parameters.Fashae and Faniran found out that bank-full width had a strong positive correlation with wetted perimeter and cross-sectional area, bank-full depth (maximum) also enjoyed a positive correlation with hydraulic radius, wetted perimeter and cross-sectional area and yet another strong positive correlation existed between gradient and discharge (Fashae and Faniran, 2015).The study ascertains the extent of variability in the morphologic characteristic of River Ogun which provides a sound basis for river maintenance and management.
A group researcher compare the morphology of braided and meandering threads of streams from the Bayanbulak Grassland, Tianshan, China; a basin where meandering and braided gravel-bed streams coexist under the same climatic and geological settings (Me tivier et al., 2015).They carried out measurements of the rivers discharge, width, depth, slope and grain size at two different periods and for the same month of the year, during high flow season to enable comparison.A group researcher measure the cross-section and the water discharge of large streams, using a 2Mhz acoustic Doppler current profiler (ADCP, Teledyne-RDI StreamPro) and in shallower streams, they used wading rods, rulers and floats to measure the surface velocity and estimate the vertically-averaged velocity from it (Me tivier et al., 2015).Topcon theodolite with a laser rangefinder was used to measure the long profile of the streams and estimate their slope.They also measured the grain-size distribution from surface counts and extracted the median grain size and the size of the 90th percentile from these distributions.Some researchers carried out a study on how the large wood in rivers influenced flood hazards (Ruiz˗Villanueva et al., 2014).They observed that in terms of flood hazard, the presence of large wood (logs, trees, branches and roots) in rivers may aggravate the consequence of flood events as these materials may affect infrastructure such as bridges, weirs and culverts, especially those intersecting forested mountainous rivers.They suggest that the presence of these woody materials in rivers must be managed and included in flood hazard and risk analysis rather than the practice of systematically removing wood debris from river channels as preventive measure, since studies have shown that this practice may be useless as the materials are transported and deposited after each flood and may not even be of benefit to the long-term natural balance of the river ecosystem.
Hence, present a comprehensive methodological approach to studying the role of large wood in rivers with a focus on flood hazard, which involves firstly, understanding the dynamics of wood recruitment, the contributing areas delivering wood to the stream have to be delineated and the recruitment mechanism studied (Ruiz˗Villanueva et al., 2014).This enables estimates to be obtained of the potential volume of deliverable wood.Then to analyze wood transport they present a numerical model, which allows simulation of the behavior of individual pieces of wood together with hydrodynamics.Finally, they analyze the impact of wood on the magnitude of flood events (in terms of water level, flow velocity or flooded areas) using a known flood event.They found out that the upstream water level rises by up 2 meters and reduces the flow velocity which favored debris and sediment deposition.Large wood in rivers can clog the channel and certainly influence flooding but as stated above, this is prominent in heavily forested areas not in areas where sediment transportation and deposition are the dominant processes.
River systems provide critical ecosystem sources to large populations and considerable pressure is exerted by population on these river systems through water abstraction for irrigation, pollution through industrial and urban expansion, as well as reduction in connectivity and alterations of hydrologic regimen by the construction of dams, barrages and related engineering structures.Aisuebeogun and Ezekwe attempt to explain the channel processes and dynamics of two river systems, the Sombreiro River and New Calabar River running through a rapidly urbanizing humid tropical deltaic environment in Nigeria, with visible threats from industrialization and consequent pollution (Aisuebeogun and Ezekwe, 2014).
Hydraulic processes and parameters are compared with established power function relations for hydraulic geometry, and it is discovered that the fundamental relations between channel-geometry dimensions, velocity, and flow can be expressed for the catchments.Ten gauging stations in each catchment are studied and results show that the studied catchments adjust their geometry to changing discharges.High values of coefficients of determination among variables indicate that much of the downstream variation in channel width to depth ratio can be accounted for by changes in discharge.Also in the study, the width/depth ratio is found to be related to the percentage of silt and clay in channel perimeter and that downstream hydraulic-geometry relations are in general agreement with previously published hydraulic and channel adjustment data.The Kaduna River is a major tributary of the Niger that rises from the Jos Plateau, flows in a north-westerly direction, through Kaduna State and its capital Kaduna and then southwards to join the Niger downstream at Wuya and Pategi.The river is the second trunk river within the Niger Central hydrological Area (HA II) rated after River Niger covering a total length of 612.6km as measure on satellite image as opposed to 550km reported in Wikipedia.This study is limited to that portion of the Kaduna River upstream of the Shiroro Reservoir, geographically located between latitudes 9°52ʹ38ʺN and 10°39ʹ07ʺN and between longitudes 6°52ʹ33ʺE and 8°28ʹ50ʺE as shown in Figure 1.The Kaduna River Basin lies between the 1000 mm and 1500 mm isohyets, which places the Basin within Nigeria's sub-humid zone.

Dry
To study the changes in channel planform of River Kaduna, the main type of data needed were on the river planform characteristics, these data were obtained from topographic maps covering the entire course of the river, from which the study reaches were selected.The topographic maps provided information for earlier periods of the study for which satellite images were not available.Multi-temporal satellite images covering the study were also used.To verify the reliability of the satellite images some direct ground measurements were taken on the field that was used to compare correspondent measurements on the images.Details of the topographic maps and satellite images used for the study are shown in Table 1 and Table 2 respectively.A Montana Garmin 650 handheld Global Positioning System (GPS) was used for logging the start point and endpoint of each bridge.A 30m Surveyor tape was laid in iterations until the entire width of the river was covered, and then the total width of the bridge was obtained by summing up all iterations and their excesses.The ground measurements and their corresponding measurements on the images are presented in Table 3.

Data Processing
Topographic maps and satellite images were processed to extract spatial data on the river planforms.The detailed methodology of the processes employed is discussed as follows:

Processing Topographic Maps
To extract data from topographic maps for analysis the relevant analogue maps were scanned to convert to digital format.When scanning of paper maps is carried out the resultant maps lose spatial reference and can't be subjected to analysis in Geographic Information System (GIG) domain.To analyze the scanned maps, spatial reference through the process of georeferencing were provided.Georeferencing the scanned maps define their location using map coordinates by assigning the coordinate system of the data frame to selected control points.This process allows the georeferenced raster data to be viewed, queried and analyzed with other geographic data.After georeferencing, a measure of the error-the residual error is returned.The error is the difference between where the "from point" ended up as opposed to the actual location that was specified that is, the "to point".The total error is automatically computed by taking the root mean square (RMS) sum of all the residuals.This value describes how consistent the transformation is between the different control points.

Image Processing
The satellite images utilized for this study were pre-processed as of the time of acquisition, that is, all forms of corrections, enhancement and georeferencing had been carried out on them.However, further processing was required for the images to be analyzed and this postprocessing included subset, mosaic and re-projection processes.

Data Analysis
In order to characterize the various planform variables on River Kaduna, nine reaches were selected on the portion of the river upstream of the Shiroro Reservoir.The reaches that were selected for the studies and their locations geographically defined as: The river bank limits for the study reaches were traced from the topographic maps and the satellite images.Further GIS analyses performed on the delineated bank limits involved the establishment of the centerline, based on which the channel length, sinuosity index, channel width and channel migration were calculated.Other calculations that were based on the extracted bank limits are the braiding index.

Analysis of Topographic Maps and Satellite Images
The channel outlines or bank limits of the defined segments of the river were delineated from the scanned georeferenced maps and satellite images using ArcGIS 10.3.1.Each of the digitized reaches was stored in a separate shapefile using procedures (Downward et al., 1994).Errors of exaggeration and generalization were avoided so that such errors do not yield misleading results.Based on the delineated bank limits further analyses were carried out to determine changes in planform of River Kaduna following the procedures (Clerici and Perego, 2016).

Characterization of Channel Planforms Variables
To describe the river channel planform variables the procedures of Clerici and Perego were adopted (Clerici and Perego, 2016).After delineating the bank limits the procedure is concentrated on the establishment of the centerline.The centerline was defined by joining a set of points that are plotted at equidistance from the opposite banks, created from successive iterations of parallel lines from the opposite banks of the river.The channel width is commonly defined as the length of the line from bank to bank orthogonal to the channel centerline.The same procedure as described in the script was used by Clerici and Perego and is adopted in this work for calculating river width, Sinuosity Index, Braiding Index and Channel Lateral Migration (Clerici and Perego, 2016).The rest of the procedure explains; Parallel lines tracing from bank limits in a series iteration, Centerline extraction, Equidistance point setting on the centerline, Orthogonal transect tracing on the centerline.

RESULTS AND DISCUSSION
The natural and anthropogenic processes acting on the river that brought about changes in the planform variables for the period 1962 to 2017 are presented and discussed under channel width, sinuosity index, braiding index, channel migration and channel length.

Changes in Channel Width
The derived statistics for the changes in channel width are shown in River Kaduna is a natural alluvial river characterized by channel boundary roughness.Its hydraulic geometry is determined by the stability of the channel banks, the availability of sediment for transport, and vegetative cover, in addition to the magnitude and variability of flow (Singh, 2003).
The boundary conditions of the river provide the friction needed to reduce the viscosity of flow and slow down the lift and drag processes of the river thereby affecting the movement of sediments (bed and bank material, and cohesive material).In the absence of scouring of the riverbed the slope of the river is gradually reduced by deposition thereby affecting the flow velocity.The types of sediments being transported have also influenced the amount of deposition.Very fine sediments are carried in suspension, which can be seen in the brown colour of water during flood flows in River Kaduna, but the coarse sands and gravels are moved by lift and drag processes that rely much on the Stream Energy.
Thus, rather than River Kaduna widening regularly in response to floods or as a long-term change due to increases in surface water runoff resulting from upland development or climate change according to Konrad, assertion or in response to riparian vegetation removal from agricultural activities as asserted by the channel width was narrowing due to deposition that follows the reduction in Stream Energy (Konrad, 2012;Brooks et al., 2003;Eaton, 2006).On June 20th, 1990, the Shiroro Dam was inaugurated and this further impacted on the velocity of the river.The decrease in Stream Energy that resulted from these processes further reduced the capacity of the river to transport its load, thereby increasing sedimentation (narrowing the channel) and reducing the capacity of the river to cope with flood flows.
The situation experienced in the reaches during the period of study was exacerbated by human intervention through various forms of agricultural activities upstream as well as urbanization.The agricultural activities expose the land cover that should naturally reduce sediment yield in the basin.Particularly, meander reaches 2 and 3, straight reach 3 and braided reaches 2 and 3, had to cope with the effect of urbanization, as high runoff from the Kaduna metropolis added to the water and sediment load transported by the river.Hence, the narrowing of these reaches during the period of study is explained by sedimentation.The narrowing channel implies that more of the discharge of the river is converted to storage which results in flooding.Tiegs and Pohl examined the planform channel response of a portion of the Upper Colorado River Delta in the United States America using aerial photography and Geographic Information System analysis, while Velcu and Morosanu studied the dynamics of the minor river bed of Teslui River Romania, in relation to human factors, and they got similar results in their analyses (Pohl, 2005;Velcu and Morosanu, 2015).

Changes in Sinuosity Index
The results in Tables 6 and 7 show that sinuosity index values for meandering reach 1 in 1962, 2005 and 2017 were 1.24, 1.25 and 1.25 respectively.For meandering reaching 2 the values in 1962, 2005 and 2017 were 1.50, 1.50 and 1.49 respectively and in the years 1962, 2005 and 2017 the sinuosity index values for meandering reach 3 were 1.24, 1.24 and 1.24 respectively.The results indicate that for the 56 years being examined there were no significant changes in sinuosity in all the three meandering reaches.For straight reach 1 in 1962, 2005 and 2017 sinuosity index values of 1.03, 1.06 and 1.09 respectively were obtained.
For the same years in straight reach 2 the sinuosity values were 1.02, 1.05 and 1.06 respectively, while sinuosity values of 1.01, 1.00 and 1.00 respectively were obtained for straight reach 3 for the same period.
The results of the sinuosity index show no significant changes in sinuosity for all the reaches studied not even in straight reaches 1 and 2 that developed meandering thaweg and the river at those reaches was beginning to erode material from the outer bend and depositing them in the inner bend.This process was not significantly active in any of the reaches studied as the sediment yield to the channel was mainly of watershed/hill slope origin.However, those sinuosity values that were analyzed for both meandering and straight reaches agreed with the sinuosity ranges proposed by Sapkale and Chougule for both meandering and straight reaches (Sapkale and Chougule, 2014).
A group researchers carried out experiments to detect the effects of the changing slope and changing sediment discharge to river patterns (Petrovszki et al., 2014).They observed that slope is related to sediment discharge; and that a river will be straight if the slope and sediment discharge are low.If the slope, the water and sediment discharge increase, the river starts to meander or could become braided.It starts with the development of a meandering thalweg, and then a real meandering channel evolved, with the sinuosity of at least 1.3.Previous observations had shown that the slope reduced but sediment yield did not reduce, and the results show that the sinuosity index did not change for all the reaches.As observed by Tiegs and Pohl in their study of planform channel response of a portion of the Upper Colorado River Delta in the United States America, sinuosity adjustments were also limited during the timeframe of their study, the Upper Colorado River Delta did respond with large adjustments in channel width.River Kaduna responded by narrowing its channel (Tiegs and Pohl, 2005).

Changes in Braiding Index
The results of changes in braiding are shown in Figures 2 -4 and the derived statistics for changes in braiding are shown in Table 8.The statistics in Table 8 shows that in 1962, 2005 and 2017 in the braided reach 1, the braided index values were 0.12, 0.53 and 1.45 respectively and for the same period, in braided reach 2 the values were 0.02, 1.16 and 6.25 respectively, while for the same period in braided reach 3 the index values were 0.39, 2.79 and 9.74 respectively.
In braided reach 1, braiding as observed in 1962 was in the form of isolated few bars occurring within the channel, transforming from a more or less straight channel to a braided one.As observed in 2005 and 2017 the reach developed more alternate bars with sinuous thalweg.This is what was referred to as river metamorphosis (Schumn, 1985).The explanation for this change is that there has been an increase in peak discharge, sediment size, and sediment load causing the river to deposit its load.In braided reach 2, the river channel was quite broad in 1962 with few lateral and longitudinal bars.In 2005 and 2017 it was observed that portions of the reach had developed islands that were more than three times the width of the channel, referred to as anabranching (Schumn, 1985).Braided reach 3, showed multiple channel systems in portions of the reach that separate and rejoin the main channel to form a network.The channels were separated by islands that are more than three times the width of the channels and are therefore anastomosing (Schumn, 1985).
The reason for the braiding is that the reaches are laden with bedload, and the slope, velocity and the stream power have reduced resulting in more deposition of sediment.In addition to the sediments generated from various agricultural activities upstream and the runoff and sediment discharge from Kaduna metropolis, dam construction is another human activity that has affected the flow of the river.It was observed that the backwater effect of the Shiroro reservoir has reduced the velocity particularly, in braided reach 3 intensifying the braiding of the river in that reach.Braiding changes channel geometry so rapidly, thereby modifying the channel boundaries and floodplains.Issues and problems of braiding channels have presented management challenges particularly as economic and ecological considerations and the desire to reduce hazards (flooding) are competing.
Management strategies that have been proposed for controlling braided rivers include protecting the developed floodplain by engineered structures, mining gravel from braided channels, regulating sediment from contributing tributaries, and afforesting the catchment.Sand mining and quarry activities were already taking place in few places in braided reach 2. Sand mining could help in reducing braiding because the mined areas serve as sediment traps.When sand is mined the river deposits some of its load in the mined area and that reduces braiding and clogging of the channel.This activity leaves very deep borrow pits that serve as flood flow collection points.During floods, a considerable amount of water is trapped in the pit and this helps in reducing the effect of flooding because it increases the lag time of floods.
These results agree with those of Tiegs and Pohl who observed that channel planform response during their study was mainly channel narrowing (Tiegs and Pohl, 2005).The results also agree with the studies in which increased braiding was observed (Scorpio et al., 2015).The same causes identified for sinuosity are also responsible for braiding (Petrovszki et al., 2014).As the slope increase and the water and sediment discharge increase, the river starts to meandering became braided with time.(Mongaldip et al., 2015).
The statistics in Table 9 shows that for meander reach 1 between 1962 and 2005 the average distance of channel migration was 82.35m and between 2005 and 2017 the distance was 61.88m.For the same period meander reach 2 had average channel migration distance of 97.01m and 69.47m respectively, while meander reach 3 had average channel migration distance of 50.06m and 36.87mrespectively.The statistics in  1962 and 2005, and 56.36m between 2005 and 2017.In all meandering and braided reaches studied there was no evidence of channel expansion and bend cutoffs this was because there was minimal lateral abrasion in most of the reaches.The dominant process responsible for channel migration was the gradual migration of channel bends (Knighton, 1998).
Figures 5 -7 show gradual channel migration for meandering and braided reaches 1, 2 and 3 Channel position shifts was negligible in straight reach 3 but very pronounced in straight reaches 1 and 2. It was observed that lateral abrasion was active in straight reaches 1 and 2 which implied that slope and Stream Energy were higher being in the upper course of the river.
It was further observed that meandering thalweg developed in these reaches particularly from 2005 to 2017.Rapid vegetation removal, constant erosion and deposition of sedition from high flow discharge during floods as well as anthropogenic influences particularly agriculture favoured channel migration in the reaches.The results obtained from this study are comparable with those of Velcu and Morosanu who studied the dynamics of the Minor Riverbed of Teslui River in relation to the human factor in Romania; those of on river channel adjustments and implications for channel recovery in Southern Italy; those of on Bank Erosion and Migration Nature of the Hooghly River in India; those of on Assessment of Anthropogenic Factors and Floods using Remote Sensing and GIS on Lower Regimes of Kangshabati-Rupnarayan River Basin in India; those of who studied the Geomorphological processes and river migration in Bangladesh and the studies of Barman and Goswami who evaluated sinuosity index of Dhansiri (South) River Channel and Bank Erosion in India using Geographic Information System (Velcu and Morosanu, 2015;Scorpio et al., 2015;Mongaldip, et al., 2015;Lovric and Tosic, 2016;Das et al., 2013;Barman and Goswami, 2015).
Velcu and Morosanu attributed the channel migration to human intervention which followed the construction of a dam for irrigation (Velcu and Morosanu, 2015).The confluence points for the river Teslui and Olt were moved and this triggered a migration to the new position of the confluence.A group researcher considered channel migration to have emanated from the natural process of erosion which was attributed to limited woody riparian vegetation along the channel (Scorpio et al., 2015).

Changes in Channel Length
In this study, the length of the centerline was considered as the valley length of the river at the various reaches.The statistics in Table 6 and Table 7 show the valley lengths for meandering and straight reaches respectively.The length of the river in meander reach 1 in 1962, 2005 and 2017 was 10172.17m,10325.31mand 10267.01mrespectively.For the same period, the length of the river for meander reach 2 was 8708.30m,8599.74m and 8628.86mwhile for meander reach 3 the length of the river was 14108.35m,14062.40 and 14034.86mrespectively.The length of the river in straight reach 1 for 1962, 2005 and 2017 was 3837.29m,3926.95m and 4023.99mrespectively.For straight reach 2 in the same period the length of the river was 4880.66m4846.15m and 5117.58mrespectively and for straight reach 3 in the same period the length of the river was 4313.06m,4298.65 and 4298.97mrespectively.
A strong link exists between sinuosity and channel length such that as sinuosity decreases, the length of the channel decreases.For instance, sinuosity decreases to a minimum when an avulsion or a series of cutoffs straightened a channel.Such changes may be related to major changes of sediment load or an increase of peak discharge, but they may also be due to a progressive increase of sinuosity-with an accompanying reduction of channel gradient-to the point that aggradation and cutoffs or avulsion results.There were no significant changes in sinuosity for all the reaches studied and consequently, there were no significant changes in channel length.Velcu and Morosanu experienced a decrease in the length of the study river and explained that it was due to the migration of the confluence point of the rivers Teslui and Olt (Velcu and Morosanu, 2015).The migration of the confluence point had the effect of a meander cut-off judging from the relics of abandoned river arms and oxbows of the old river course.Barman and Goswami found that a neck cut-off had resulted in a shortening of the channel course, as it was observed that the river course in 2008 became shorter than that in 1999 (Barman and Goswami, 2015).

CONCLUSION
The results of the analysis of changes in channel planform of River Kaduna have shown that there have been significant changes.There has been a considerable amount of contraction in the meandering and straight reaches that have greatly altered the width of the river and there has also been an increase in braiding.The hydraulic geometry as expressed by Singh (2003) asserts that there is a direct relationship between channel width and discharge.The reduction in the width of the river has adversely affected the discharge pattern of the river which is manifested in an increase in water storage (floods) and erosion.Also, there is huge deposition of finer sediments in the river and this has adversely reduced the water retention potentials of the river which can result in flooding as experienced in similar locations.

Figure 1 :
Figure 1: Map of the study Area.

Figure 5 :Figure 6 :
Figure 5: Changes in Channel Migration from 1962 to 2017 for Meandering Reach 1

Table 1 :
Details of the Topographic maps

Table 2 :
Details of the Satellite Images Acquisition of Topographic Maps and Satellite Images: Topographic maps used were derived from aerial photographs of 1962 and published in 1965 by the Northern Nigerian Survey as indicated in the map reliability diagram.The maps were obtained from the Federal Survey Map Depot in Kaduna.Seven Map Sheets at scale 1:50,000 covering the study area were used namely, Kaduna Sheet 123 S. E., Kakuri Sheet 144 N. E., Kajuru Sheet 145 N. E., Kafanchan Sheet 167 N. E., Igabi Sheet 124 S. W., Geshare Sheet 146 S. W. and Alawa Sheet 143 S. E. Mosaic of SPOT 5 satellite images (5m resolution) of 2005 for the whole country was collected from the National Population Commission State Office Jos and Sentinel-2 image (10m resolution) was downloaded from Glovis-USGS free download site.Field Observation: The reliability of satellite images was verified by ground measurements using a 30m Surveyor's tape on four bridges that cross River Kaduna at Nasarawa, near Ahmadu Bello Stadium, the one popularly known as Yakowa Bridge and the Gadan Danbushiya at Unguwan Rimi.The measurements obtained, were compared with correspondent measurements on the satellite image and found that the ground measurements and the measurements on both SPOT and Sentinel images were close.Hence, the measurement of the river parameters from satellite images could be reliable.The photograph on Plate IV shows measurement being taken on the Nasarawa Bridge.

Table 3 :
Ground Measurements and Their Corresponding Measurements on The Images

Table 4 :
Statistics of Average Width of Meandering Reaches in meters

Table 5 :
Statistics of Average Width of Straight Reaches in metres

Table 6 :
Statistics of Channel Sinuosity of Meander Reaches

Table 8 :
Values for Changes in Braiding Index Braided reaches Table 10shows that in straight reach 1 the average distance in channel positional shift between 1962 and 2005 was 79.91m and between 2005 and 2017 was 23.35m.For straight reach 2 the average distance in channel positional shift between 1962 and 2005 was 122.22m and 55.28m between 2005 and 2017.The statistics in Table11shows that in braided reach 1 between 1962 and 2005 was 99.70m and between 2005 and 2017 was 86.06m.

Table 9 :
Statistics of Average Distance of Channel Migration of Meander Reaches in meters.

Table 10 :
Statistics of Average Distance Channel Migration of Straight Reaches in meters.

Table 11 :
Statistics of Average Distance Channel Migration of Braided Reaches in meters.