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ORIGINAL RESEARCH article

Front. Water
Sec. Water Resource Management
Volume 6 - 2024 | doi: 10.3389/frwa.2024.1455763

Urbanization and hydrological dynamics: A 22-year assessment of impervious surface changes and runoff in an urban watershed

Provisionally accepted
Omwoyo Ongaga Omwoyo Ongaga 1*Mary Makokha Mary Makokha 1Kennedy Obiero Kennedy Obiero 1Isaac Kipkemoi Isaac Kipkemoi 2*
  • 1 Kenyatta University, Nairobi, Kenya
  • 2 University of Embu, Embu, Kenya

The final, formatted version of the article will be published soon.

    The frequency and intensity of flooding has been increasing in urban watersheds. Urbanization disrupts natural landscapes by replacing vegetated areas with impervious surfaces thus reducing infiltration and increasing runoff. The objective of this study was to evaluate the relationship between change in impervious surface area and runoff amount of Mihang’o watershed located in the outskirts of Nairobi from the year 2000 - 2022. The specific objectives of this study were: To determine change in impervious surface area of Mihang’o watershed, trend of precipitation amount in the watershed and the trend in runoff amount, a major source of flood water from the watershed. Supervised classification was done on Landsat images to determine percentages of impervious surface cover for the study period and linear regression analysis was used to establish the trend. CHIRPS rainfall data was retrieved from Google Earth Engine then processed to produce monthly and annual rainfall totals then Mann-Kendall trend tests were used to establish the rainfall trend for the watershed. The HEC-HMS model was used to simulate runoff from the watershed with the rainfall data and impervious surface area percentages as inputs then linear regression analysis was done to establish the runoff trend. The Impervious surface area increased by 87.03% from 2.88% (0.49 km2) of the total surface area of the watershed in 2000 to 22.21% (3.91 km2) in 2022 demonstrating an approximate increment of 3.96% (0.88 km2) each year. The Mann-Kendall trend tests results (Sen’s slope results (β = .832), Kendall’s tau results (τb = .146), and p-value (.625)) confirmed that there is no significant change in rainfall amounts. Runoff increased by 84.75% from 0.18 mm in 2000 to 1.18 mm in 2022, otherwise an approximate increment of 3.85% (0.045 mm) each year. Besides the impervious surface area, the HEC-HMS model factors in length of slope, length of reach, soil type, size of sub-basins, and longest flow path, thus producing accurate estimations of runoff.

    Keywords: HEC-HMS model, Rainfall - runoff, Impervious and pervious layers, Urban, Watershade, Hydrological dynamics

    Received: 27 Jun 2024; Accepted: 31 Oct 2024.

    Copyright: © 2024 Ongaga, Makokha, Obiero and Kipkemoi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence:
    Omwoyo Ongaga, Kenyatta University, Nairobi, 00100, Kenya
    Isaac Kipkemoi, University of Embu, Embu, Kenya

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