Browsing by Author "Mireri, Caled"

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    HEC-RAS Modeling for the Determination of Highest Water Mark as the Reference Surface for Delineation of Riparian Reserve: Case Study of Nairobi River-Kenya
    (African Journal on Land Policy and Geospatial Sciences, 2025-05) Odongo, Malachi; Mireri, Caled
    Context and background: Highest Water Marks (HWM) has often been used as the points of reference for measurement of the width of the riparian reserve. Its determination is usually a challenge and, in most cases, its often approximated manually by physically going to the river banks during heavy rainfall seasons. This has often caused a huge challenge when delineating riparian reserves for purposes of protecting and conserving it. Hydrological Engineering Centreline River Analysis System (HEC-RAS) has proven to provide accurate simulation of the highest water mark over a long period of time using both geomorphological features and climatic data. Goal and objectives: The main aim of this study was to apply HEC-RAS model to determine the highest water mark (HWM) for Nairobi River for a flood return period of 30 years. Methodology: HEC-RAS version 6.3 was used to simulate the HWM with inputs of the Digital Terran Model (DTM), River Discharge and rainfall gauge station data. The model was found to very suitable for determining the HWM after conducting validations during the high rain fall periods of April/May 2024 which caused a heavy flood in Nairobi City. The HWM was then used to offset the different set back distances of 2m, 6m and 30m as per the legal framework and laws governing riparian delineation. Levels of encroachment was then established within those delineated riparian reserves. Results: The upper river segment, the highest water mark was found to range between 2-3m above the river bed on a well V-shaped river slope hence not susceptible for flooding while the middle river segment the highest water level was above 5m on a U-shaped river slope rendering it a flood plain where as the lower river segment the highest water mark was found be 1.5m above the river bed on a widened U-shaped river slope making it very prone to huge floods.
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    Land Use and Land Cover Changes Using Orfeo Tool Box Open-Source Classifier within an Urban River Riparian Reserve of Nairobi River, Kenya
    (Journal of Geography and Regional Planning, 2025-03) Odongo, Malachi Atieno; Mireri, Caled; Mwangi, Patricia
    Urban riparian reserves are a vital source of ecosystem services for urban dwellers. These zones support urban food production, environmental quality, and are home to rich biodiversity of flora and fauna. Even though urban riparian zones offer many benefits to the urban dwellers, the same zones are under tremendous threats from increased anthropogenic activities resulting from Land Use Land Cover (LULC) changes. Nairobi River is a perfect example where urban pressure emanating from the expansion of Nairobi City has undergone immense LULC changes for the past 20 years. Therefore, remotely sensed data could be used to provide detailed information for changes caused by human activities especially within riverine environment using open-source classifiers such as Orfeo Tool Box (OTB). OTB is an essential open-source Remote Sensing tool in assessing the impacts of changes in urban LULC on the environment. High resolution aerial imagery epoched at 2000, 2010 and 2020 was used to detect and assess information about the predominant LULC, their changes over the years and their potential causes. Four LULC classes of bare-land, vegetation, built up and water were identified and analyzed over a 28 km stretch of Nairobi River segmented at the lower, middle and upper based on the topography. The lower section had the most drastic land use changes especially for the built up and vegetation which both increased steadily at 1 and 1.5% annually, respectively eating up both bare land and water which declined at the rate of 1.7 and 0.8% respectively. Likewise, the middle section was equally found to be invaded by double increase of both built up and vegetation at 2 and 3% for the same 20-year period. On the contrary, the upper section of the Nairobi River area was dominated by urban agriculture which covered almost 50% and increased further to 62% over the period registering a growth of approximately 12% translating into 1.2% per annum. This signifies rapid depletion of the riparian reserves which needed an enforcement mechanism and harmonization of various laws and policies for riparian conservation.