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INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES
Volume 7, No 1, 2016
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article ISSN 0976 – 4380
Submitted on May 2016 published on August 2016 43
Integrating GIS and remote sensing in environment impact assessment of
Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri1, Charles N. Mundia1
1-Dedan Kimathi University of Technology, Institute of Geomatics, GIS and Remote Sensing
ABSTRACT
GIS is increasingly being used worldwide within Environmental Impact Assessment (EIA);
However, the extent has not been well documented and therefore not well appreciated in the
scientific fraternity. In this case study the National Water Conservation and Pipeline
Corporation (NWCPC) on behalf of the Kenyan government engaged a consultant to identify
a suitable site for a mega dam to supply water to the proposed Isiolo resort city. The
consultant decision in siting the dam was not based on a comprehensive scientific analysis, as
required of such a project. This could be one of the many other projects being implemented in
the wrong premise courtesy of politics, and influence of leaders. The objective of this study
was to review the E.I.A process carried out by the consultant to determine whether any
scientific technique was employed on the identification of the ideal site for the dam. The
Ewaso Nyiro basin was identified and the relevant data on dam siting collected and processed.
Spatial analysis was used to inform the location of the dam based on weights realized through
the Analytical Hierarchical Process (AHP). The analysis realized three suitable dam sites that
were further subjected to analysis based on the local conditions to finally settle at the most
suitable site for the Mega-Dam. The site slightly differs from the one fronted by the
consultant in terms of capacity, inundation area, and dam crest length. The study has revealed
that the most ideal site was within vicinity to the site identified by the contractor. Decisions
taken regarding the length of the dam wall were noted to be misleading since no scientific
approach was adopted. There is danger of implementing very noble, gigantic and capital
intensive projects in the wrong premise when wrong decisions are made based on unscientific
means.
Keywords: AHP, Dam Siting, EIA, Spatial Analysis, Remote Sensing and GIS.
1. Introduction
The principles of sustainable development are aimed at balancing between economical, social
and environmental issues. This balance is achieved by conducting a critical examination on
the effect of the project on the three issues. Environment Impact Assessment (E.I.A) is one
method of enhancing sustainable development. Effective EIA study is used as an integral
strategy for building control and assurance throughout the project. Project proponents can
failed to scientifically determine the suitable site as required. If the E.I.A is not properly
conducted it would not be possible to successfully predict the likely changes on the
environment as a result of a development. It would also not be possible to select the best
alternatives from the available options. The compatibility of the project with the environment
would also not be determined. Without proper E.I.A, it would not be possible to propose
mitigation measures due to impacts on the Environment. Dam construction has a potentially
serious effect on the floodplain forests and their resources which indirectly affect the
discharge downstream (Adams, 1989).There are three main steps of working in a project i.e.
Investigation of the site, design and construction. This case study mainly dwelt on the
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 44
investigation part of the project. The investigation includes the meteorological, hydrological,
topographical and geological investigations on the watershed basin being considered for dam
construction (Narita, 2000). A dam project is determined by considering various factors
associated with topography and geology of the dam site. Detailed information regarding the
topography, drainage network, channel length, water divide, geo-morphological and
geological set up of the area for proper watershed management and implementation plan for
water conservation measures are evaluated (Singh et.al, 2014).
Ewaso Nyiro basin falls on an arid and semi – arid landscape which is a fragile ecosystem,
sensitive to degradation and desertification. Loss of productivity results from complex
interaction between climate impacts and unsustainable land use practice. Different factors
play a greater role depending on the specific situation. There are certain parameters that apply
globally while others vary depending on the local conditions. It is therefore very necessary
that in-depth study is carried out to determine what parameters apply in prevailing conditions
and how to get the best out of such conditions. GIS and Remote sensing technology provides
economics of scale for monitoring, analyzing, and in some cases quantifying the parameters
needed to characterize natural and human-induced environmental changes (Michael, 2000).
Macharia et.al (2015) noted that expert opinion ought to be sought from different groups of
experts based on their professional knowledge. The Analytic Hierarchy Process (AHP) is a
multi-criteria decision- making approach solve complex decision process (Saaty, 1980).
2. Study area
The Area under study shown in Fig.1 covers four counties in the Kenyan Rift Valley and
Upper eastern regions of the country comprising Isiolo, Meru, Laikipia, and Samburu
counties, covering an area of 25 336.1 square Kilometers. The population in the study area
was 143,294 according to 2009 population census. Ewaso Nyiro is the largest catchment
basin in Kenya with the least population. The spatial distribution of rainfall varies from
800mm/year in the highlands to 400mm/year in the Arid and Semi Arid Lands (ASAL) areas.
The Ewaso Nyiro is the main river in the basin and the name is derived from the Maasai
name for brown or muddy water. Ewaso Nyiro is the third largest river in Kenya and has
twenty tributaries. The main economic activity for the region is pastoralism and the Ewaso
Nyiro River provides a livelihood to the community living in the region. Isiolo town where
the resort city is proposed is currently served by Isiolo water supply constructed in 1980 -
1983 to serve a population of 15,000 persons. The population has been on the increase and
has since grown to 60,000 persons according to 2009 population census (KNBS, 20`0), and
as a result the water demand has far exceeded the production capacity of the existing water
supply. It is important therefore to mitigate on the water shortfall currently being witnessed in
the region partly because of the proposed resort city and for reasons of future generation.
3. Methodology
The study has employed a number of processes to determine the suitable sites as shown in
Fig.2. Literature obtained from different sources singles out four (4) main factors that should
be considered during the process of dam siting. These are geological, topographical, climatic
and demographic factors. The Kenya counties map was sourced from survey of Kenya.
Scanning, digitizing and georeferencing were done on the hard copy to come up with the geo-
referenced county map in soft copy. The boundary outline for the four counties being
considered for the study i.e. Isiolo, Laikipia, Meru, and Samburu were used to clip all other
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 45
data sets that were included in the study. The acquired climatic data composed of rainfall and
temperature in an excel spreadsheets. The spreadsheets were converted to ‘csv’ format for
uptake in ArcGIS. Interpolation was carried out to predict values of the unmeasured locations
by using Kriging method. Kriging interpolation assumed that the interpolated surface was
homogenous across the surface and applied weighting based on the distance. Reclassification
was done by assigning zones with higher rainfall output as suitable because of water supply
to the dam, while compared with low rainfall. Zones with low temperatures were considered
prime zones for dam construction because of lower evaporation when compared with zones
of higher temperatures. Population data obtained from the Kenya National Bureau of
Statistics was in excel spreadsheet.
Figure1: Study area
A column of Population density was deduced from the total population and the areal extent.
The spreadsheet was converted to ‘csv’ and rasterized. Zones that are sparsely populated
were considered more suitable than areas that are densely populated, because of reduced mass
transfer of population during construction. Data containing soil drainage and texture was
defragmented to deduce the individual characteristics. Excessive well drained soils were
considered more suitable than poorly drained soils because of retention reasons. The
reclassification was then done. Soil texture with high concentration of clay are considered
more ideal for dam construction because they provide better permeability and water loss
retention than sandy soils.
Six (6) LandSat 8 images (accuracy of 30m) were downloaded from USGS website. The
images were uploaded to Erdas Imagine 10, where radiometric and image enhancements were
first carried out (Pre-processing). Layer stacking was done where different spectral bands
were combined for the layer; for example band 1, 4, 7 were used for the forest. The stacked
imagery mosaic was created and used to create a subset using the study area boundary map.
Supervised classification was done by first identifying the specific homogeneous
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 46
representative samples of different land cover types of interest. These ‘training sites’ were
isolated and mapped during ground truthing. Signatures were created from these training sites
vide the signature editor. The classification was then done to achieve the eleven (11) classes
of the land cover i.e. woodland, towns, swamp, plantation, grassland, forest, bush land
(sparse, bush land (dense), barren land (S/G), barren land (R), agriculture (sparse), and
agriculture (dense). The supervised classified image was converted to a polygon in ArcGIS
10.3. The Catalog was used to create an inventory for the processed data. Expert opinion was
sought through a questionnaire from different sources. Pair wise comparisons were
formulated to determine the relative importance of each criterion. These comparisons were
used to obtain the weights of importance of the decision criteria, and the relative performance
measures of the alternatives in terms of each individual decision criterion.
These pair wise comparison were based on the Thomas Saaty scale of 1-9.Spatial modeling in
ArcGIS Model builder analyzed the different variables independently and collectively to
obtain the suitable site map as a weighted overlay. To pinpoint the exact position to locate the
dam, further analysis was required to identify the most suitable site guided by Food and
Agriculture Organization (FAO) guide on dam siting. A comparison between the contractor’s
site and the ideal site identified by the analysis was done to determine whether the two sites
differ in terms of elevation, capacity and crest length. The comparison highlighted the
differences and similarities between the two sites.
4. Results and discussion
4.1 Variables criteria results
The slope of the Ewaso Nyiro river basin as shown in Fig. 3 is predominantly flat with gentle
slopes covering the large section of the basin. The low lying areas (1° - 20°) are preferred
more for dam construction than the high lying areas (40° - 78°). The largest proportion of the
study area comprise of bush land 60.6% as shown in Fig. 4. The statistics on land cover
show that 1% is under swamp, 5% woodland, 10% plantation, 5% grassland and less than1%
settlement. Agriculture takes paltry 4% of the area being considered for dam construction.
This will definitely improve with irrigated agriculture from surplus water from the dam.
The soil distribution in the area under study as shown in Fig. 5 indicates that the largest
proportion of the soils is well drained and amounts to 75%. Excessively drained soils
constitutes -7%, poorly drained -5% ,moderately drained -11%, very poorly drained - 1% ,
very poorly drained and imperfectly drained soils constitutes a dismal 1% of the soil
distribution.
Well drained soils are preferred in the construction of the dam because of water retention
consideration. The soil texture distribution shown in Fig. 6 indicates that the area under
study has good clay. The statistics on soil texture demonstrates that clayey soils constitute
75.5%, very clayey 8%, loamy 6.5% and sand 10%. Soils with high concentration of clay are
considered to be good for dam construction because they provide permeability necessary for
water loss prevention. Very clayey soils in the component are therefore given more
preference than sandy soils that have poor water retention capabilities.
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 47
Figure 2: Slope Mape Figure 3: Land use cover map
Figure 4: Drainage map Figure 5: Soil texture map
Climate data obtained from the meteological department comprised of rainfall and
temperature. The mean of each component for the past thirty (30) years was used to deduce
the climatic condition for the basin. Temperature contributes to the evaporation of the water
mass and therefore must be considered. Over 90% of the basin is covered by mean
temperatures of above 24°C, however cooler zones (19°C - 24°C) constituting the 10% was
given more preference than zones of higher temperatures. Ewaso Nyiro river basin falls
generally on a semi-arid area that experiences little rainfall of not more than 360mm within
the year. Areas with prevalent higher rainfall were considered more ideal for siting the dam
than areas with less rainfall (below 50mm annually). Rainfall provides water that fills up the
dam and without rainfall rivers will not flow, and therefore makes dam construction along the
river impossible.
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 48
Figure 6: Temperature map Figure 7: Rainfall distribution map
The Population density for the catchment area and the entire Ewaso Nyiro river basin was
considered. Zones with scanty population (0-138 persons per Km2) would have minimal
relocation to the population to pave way for the dam construction and are therefore preferable
more than areas with dense population (415-554 persons per Km2).The Euclidean distance to
the river was considered among the other variables to determine the ideal site for the dam.
The ideal site was considered to be within a radius of one kilometer from the river.
Figure 8: Population Density Figure 9: Map showing distance to the river
4.2 Weighting
To determine the weights for use in modeling, the expert opinion extracted from the
questionnaires was analyzed, assembled and tabulated as pair wise comparison between the
eight variables considered. The independent comparisons between the eight variables were
tabulated to form the 8*8 matrix as shown in Table 1.
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 49
Table1: Tabulation of Eigen variables
Population Soil
Texture Slope Temperature Rainfall
Distance
to River Drainage
Land
Cover
Population 1 1 2 8 6 5 3 8
Soil Texture 1 1 5 3 8 4 1 6
Slope 0.5 0.2 1 5 8 8 0.2 8
Temperature 0.125 0.333 0.2 1 0.333 7 0.167 9
Rainfall 0.167 0.125 0.125 3 1 3 0.125 5
Distance to
River 0.2 0.25 0.125 0.143 0.333 1 0.125 0.5
Drainage 0.333 1 5 6 8 8 1 3
Land Cover 0.125 0.167 0.125 0.111 0.2 2 0.333 1
Weights were deduced from the normalized matrix by carrying out calculations based on the
Saaty dissertation. The outcome of the weights as shown on Table 2 indicates that the experts
considered population, soil texture and drainage to be of more importance than slope,
temperature, rainfall and distance to the river. The degree of preference is as indicated as a
percentage and the weights are derived there from. The obtained weights were then used in
the spatial modeling process in the weighted overlay of the model builder.
Table 2: Final variable weights from AHP
4.3 Modeling
The spatial analysis was executed on the model builder to achieve the suitability map shown
in Fig. 11.The suitability map shows various zones within my study area with varying
suitability outcomes. Areas covered by blue shades are more suitable for the dam than zones
covered by pink shades. The analysis demonstrated graphically in Fig.12 indicates that less
suitable sites constitute the biggest margin (53.8%) of the areas sought for dam suitability.
Moderately suitable followed with 34.8%; Suitable site managed 9.6%; Unsuitable site tailed
together with the most suitable site with 1.5% and 0.3% respectively. It was envisaged at the
beginning that the dam will be located on the most suitable site but because of the marginal
score (0.3%), it was found necessary to consider the next available option of suitability i.e.
Weights %
Population 0.232978 23%
Soil Texture 0.210137 21%
Slope 0.145848 15%
Temperature 0.10196 10%
Rainfall 0.05379 5%
Land Cover 0.015914 2%
Drainage 0.220581 22%
River
Distance 0.01879 2%
Total 1 100%
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 50
the suitable site which had a good score of 9.6%. The ideal dam site has been considered in
these two zones (i.e. most suitable-0.3% and suitable-9.6%).
Figure 9: Suitability Map Figure 11: Suitability Graph
4.3 Site analysis
The maximum crest length for the wall on sub-surface dams depends on the geological
formation and stability thereof. Based on statistics on a number of reservoirs done in Kenya,
the maximum crest length for the dam to achieve 215 Million Cubic Metres is approximated
to be 1000m.Thorough investigation on the suitable sites that can achieve this condition is
conducted by investigating the behavior of contours along the identified suitable sites. The
contours were generated within the suitable sites, and a close scrutiny on the curvature done
in view of identifying the sites where contours bounds themselves by leaving a minimal neck
of not more than 1000m.
Figure 12: Contour Polygon on TIN Figure 13: Analysis on contours
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 51
The feature polygon was created by closing the contour at the neck identified as shown in Fig.
14. The neck of the uploaded contour was identified and measured to determine whether it
meets the desired criteria in terms of length. All the contours enclosed by the outer contour
(ideal contour forming the reservoir) are selected and removed to pave way for a single
polygon. The contour line was then closed at this point to create the Dam wall and the
polygon was used in volume calculation. The best ideal dam site attained the desired volume
and even exceeded the mark by 20.5 Million cubic Metres. Three tributaries of the main river
met at the main channel at this site making the dam site more desirable for maximum storage
capacity. However, before concluding that this would be the ideal site, it was prudent to
investigate the discharge of the river at this site and determine whether the flow would meet
the demand of filling the dam within one year.
Figure 14: Volume calculation on the reservoir
Figure 15: Graph showing the mean discharge of Ewaso Narok (Depattas) and Ewaso Nyiro
River at the confluence of Ewaso Narok and the Main Ewaso Nyiro tributary.
The ratio of annual inflow of water to the storage capacity was considered according to
(Nicholas, Undated). This should not be too high or too low. The ratio should range from 1:1
to 1:5 otherwise the reservoir would never fill up or have a situation where large outflows are
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 52
witnessed on the spillway. To attain this volume a discharge capable of attaining the 235.5
Million cubic metres was required. The minimum annual discharge = (235500000/
(364*24*60*60) = 7.46 M3/Sec. To investigate this matter, discharge data from River gauge
station 5DC01 (Confluence of the Ewaso Narok and Ewaso Nyiro) and station 5BC04
(‘Depattas’) were obtained from the WARMA in full and analyzed to determine the
suitability of the site in terms of the discharge capability.
To ensure that the reservoir is filled up within one year, discharge values from 1963-2013
were investigated. The level of discharge capable of filling the reservoir was not attained in
1970, 1972-74, 1984, 1991 and in 1999-2006, as demonstrated in Fig.17. A dramatic increase
in discharge has been noted from 2007-2012, although a huge drop was witnessed in 2013,
though not significant to affect the required flow to the reservoir. The discharge between 199-
2006 was too low even in some instance below the discharge of the Ewaso Nyiro tributary at
Depattas. It is therefore evident from the flow regime of the Ewaso Nyiro River that the
required capacity can be achieved. My ideal dam site falls on the same area considered by
CAS Consultant Ltd. The consultant had considered elevation 1580m asl as the dam crest
elevation and maintained that at this level, it was possible to attain a dam crest length of
850m. The minimum crest length that can be attained at this level is however 1.14 Kms and
not 850m as alleged.
That is the reason why I have adopted contour whose elevation is lower (1570m asl) to
achieve a crest length of 785m which is below the maximum value adopted. Reducing the
crest length to the proposed 850m will mean additional cost to the project and compromise
the stability of the wall. The storage capacity on the 1580mm asl dam site proposed by the
CAS Consultant Ltd is of course higher by 76.5 million cubic meters from my proposal. It
also covers a larger area than what I had achieved for inundation (905.6 Ha.). The sites are
well elevated to provide natural flow (gravity) of water from the reservoir to the resort city.
My site offers an opportunity for the National Water and Pipeline Corporation (NWPC) to
engage an engineering firm to carry out designs and engineering works on the two sites and
immediately embark on the construction of the Mega Dam as envisaged by the Vision
2030.The dam site identified, meets all the desired criteria identified for the dam siting. The
site also offers a better opportunity because the elevation of 1400m asl is well above the
resort city. The proponent should also consider drilling wells downstream to allow people
living downstream to access water that may otherwise be lost through seepage. Fencing the
dam and reservoir may be required to prevent access to the embankment and reservoir.
Involvement of the beneficiaries in any remedial or mitigation works also engenders a sense
of responsibility in using and maintaining the water resource provided. Dam construction
disturbs the landscape around the dam and these should be kept to a minimum. It should be
part of any contract for the contractor to remove and store the topsoil of any area to be
disturbed and then return such topsoil to the site to allow normal vegetation to re-grow and
prevent any subsequent erosion.
Community participation is important for the successful implementation of the projects. The
communities downstream are not actually opposed to the project as such, but they feel
sidelined in the planning stage for this noble vision 2030 project. From the complaints raised
on this project, it is evident that the views obtained from the stakeholders were not
representative as demonstrated on the report. Representative views, not just that of land
owners but also those who will be most directly affected or benefit from the dam should be
consulted to determine their needs and views. The issue of river Ewaso- Nyiro drying up
downstream due to the construction of the dam is a non-issue because an investigation during
Integrating GIS and remote sensing in environment impact assessment of Ewaso Nyiro Mega dam in Kenya
Daniel Maina Mukiri et al.,
International Journal of Geomatics and Geosciences
Volume 7 Issue 1, 2016 53
ground revealed that the river had dried up even before reaching Archers post bridge and the
dam is yet to be constructed.
5. Conclusion
This study sought to investigate using spatial analysis a suitable site for the dam among the
five sites speculated by project proponent. The E.I.A report did not adduce any scientific
evidence to demonstrate on how they arrived at their conclusion to locate the Mega –Dam at
‘Crocodile Jaw’ dam site. The decision could be based on past experience, influence from
powerful personalities in the society, local politicians, and administrators. There is danger
therefore if a project of such a magnitude of investment is located in the wrong location
because it would fail to attain its desired objectives. The aim of the study was to demonstrate
how GIS and Remote Sensing applications could be integrated in Environment Impact
Assessment (EIA). It has addressed the three research questions on criterion of dam siting
and whether the dam site identified by the contractor was ideal or not. Expert opinion and
literature materials were relied upon to determine the criterion to site the dam. Four primary
factors namely geological, topographical, climatic and demographic were identified as the
most critical areas to consider while siting a dam site. Data sets related to these factors were
sought and collected respectively as follows: - Soil data vector layer, topographical maps,
LandSat 8 and SRTM image, climatic and population data.
The output was applied in the Analytic Hierarchical Process (AHP) technique to derive the
weights used on the weighted overlay. Each variable was independently treated in modeling
and collectively on a weighted overlay to produce the suitability map. Among the most
suitable sites, three sites were identified and further analyzed to determine their suitability in
terms of size, volume and capacity. They were then compared with the site identified by the
project consultant. This case study has demonstrated that GIS and Remote sensing techniques
are valuable tools in decision making process for the determination of suitable site within a
given environment. Both GIS and remote sensing provides a wealth of environmental data
over a range of spatial and temporal scales and therefore play a major role in the provision of
indicators on environment conditions.GIS has a powerful visualization capability that allows
themes to be viewed in a spatial context and enable alternative viewpoints like deciding on
the contour line to adopt for the dam. The entire river flow and release in the dry season
should be further investigated to ensure the maintenance of downstream watercourse in as
natural condition as possible. The enquiry should put to end the fears of the pastoralists living
downstream.
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