Assessing Morphological Changes of the Msimbazi River Using Satellite Images

Abstract

This study assessed historical morphology changes of the Msimbazi River in Dar es Salaam City, Tanzania, following heavy rainfall events using historical Google earth images. The erosion and sedimentation processes that cause morphological changes of a river are also associated with flooding within the river catchments. In this study, the bank-line movement, erosion and sedimentation areas and changes in river section width were analyzed under three-time periods: 2005- 2012, 2012- 2018, and 2018- 2020. Data shows that, the timing for floods coincides with the historical records for heavy rains. It was found that, area in the upper reaches of the river such as Kinyerezi suffer from river bank erosion most, as indicated by the large increase in river width. This has resulted into washing away of infrastructure including houses and loss of land. The river channel width at Kinyerezi has widened a lot since 2005, with some sections having widths of more than 90 m. On the lower reaches for example around Kigogo and Jangwani areas, deposition of the soil materials prevails, resulting into raised river bed and reduced river widths. As the river section an hence carrying capacity is reduced, inundation of river banks occurs. This is among the causes of river bank flooding reported at these areas whenever there is a heavy storm event. It is therefore recommended that interventions to solve the flooding events in Dar es Salaam city should also include preventing catchment and river bank erosion on the upstream areas.

Analysis of Msimbazi River Banks Erosion with Regards to Soil Erodibility

“…Some of the sample collected at Kigogo and Jangwani had no clay content while other had only sand as it can be seen from Table 2. The result of soil analysis for this section is in agreement with the fact the downstream of Msimbazi River suffer from high load of sediment and di culty of dredging that obstruct the natural river ow (Izdori et al, 2022;Valimba & Mahe, 2020).…”

“…4, 5 and 6. Some sections especially from the Kinyerezi area faces severe river bank erosion due to morphometric change of the Msimbazi River (Izdori et al, 2022;Thakur et al, 2012).…”

“…3C. The river has a variable river width (Izdori et al, 2022) where Kinyerezi section had a wider river section with very high terrace than other two sections (Fig. 3).…”

“…Kinyerezi section, which is at the edge of rapid change in elevation from upper basin to lower basin (Figure 2a), Kigogo section, which is the highly encroached section (Figure 2b) and Jangwani section upstream of the mouth of the river, crossing the major road connecting the city centre and other sub-urban areas (Figure 2c). The lower Msimbazi basin has been experienced rapid geomorphological changes, meaning the selected study area was subject to recurrent erosion and sediment deposition (Izdori et al, 2022;Paul et al, 2020). River bank characterization was done to understand the physical parameters of the selected river section and its relation to river bank erosion.…”

“…(Izdori et al, 2022;Thakur et al, 2012). Large part of the river is encroached with housing right on top of the banks (Fig.…”