River Flood Modelling with Mike 11: Case of Nzoia River (Budalangi) in Kenya

This paper presents a one-dimensional unsteady flow hydraulic model used for the simulation of flow in rivers: the MIKE 11 model from the Danish Hydraulic Institute (DHI). The approach used for this model leads to unsteady flow simulations along river channel reach. The study case applied to the model is the lower Nzoia River, about 25 km in length. The study’s focus was the development of a MIKE 11 river model based on surveyed river cross-section data. The flooding problem in the lower Nzoia (Budalangi floodplains) in Kenya has been perennial each time causing a reversal of gains on economic and social development. The main objective of this study is to implement a one dimensional hydrodynamic model for the lower part of Nzoia river using the MIKE 11 modelling software. This was done with an aim of investigating the nature of the 2008 Budalangi floods. Two scenarios were considered, namely; reference case (intact dyke) and the breached dyke case. Longitudinal river stretch profiles were produced for the two cases and it was conclusive that the 2008 flooding was mainly necessitated by dyke breach. Further, the optimal computational spatial step (?x) and time step (?t) for the model were found to be 500m and 1 minute respectively. For this condition no instability of the model simulation was observed. Key words: Nzoia River, MIKE 11 hydrodynamic model, Budalangi, floodplains, river hydraulics, unsteady flo

Analyses of rainfall trends in the Nile River basin

Trends in rainfall at 39 locations of the Nile River Basin (NRB) in Africa were analyzed. Comparison was made between rainfall trend results from the long-term data and those of short-term series selected over different time periods. The bias on trend results from series of short-term records was quantified. Homogeneity test was conducted to assess the coherence of the trend directions on a regional basis. Based on an assumed population (for simplicity) of rainfall data time periods in the range 75–100 years, bias in the short-term trend analysis was noted to reduce by about 10% for every 10% increase in record length. Under some conditions if respected, it was possible to derive trends at stations with short rainfall records based on those at nearby stations with longer term records but in the same region. Using the same data record length and uniform time period at all the selected stations, an improved regional coherence of rainfall trend results was obtained. In the equatorial region, trend in annual rainfall was found mainly positive and significant at level α = 5% in 4 of the 7 stations. Collectively for Sudan, Ethiopia and Egypt, trends in the annual rainfall were mostly negative and significant at α = 5% in 69% of the 32 stations. Heterogeneity in the trend directions for the entire NRB was confirmed at α = 1% in 13% of the 39 stations. These findings are vital for water and agricultural management practices.publisher: Elsevier articletitle: Analyses of rainfall trends in the Nile River Basin journaltitle: Journal of Hydro-environment Research articlelink: http://dx.doi.org/10.1016/j.jher.2015.09.002 content_type: article copyright: © 2015 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.status: publishe