Resilience Scanner

Msimbazi River Water Level and Conductivity Monitoring System

Solution Overview

A water level logger was installed underneath the Selander Bridge at the outfall of the Msimbazi River to measure water levels and conductivity (salinity) for a period of at least one month.[1][2][4] This monitoring technology formed part of a comprehensive survey campaign conducted by the Tanzania Urban Resilience Program, which employed an innovative combination of Light Detection and Range (LiDAR) UAV surveying and bathometric surveying to support flood modelling within the flood-prone Msimbazi river basin.[5] The approach addressed critical data gaps in understanding flood dynamics in an area experiencing frequent, severe flooding at least twice a year during every rainy season, with nine major flood events taking place in 2019 alone.[9]

Technical Components

The water level logger installation prioritized vertical referencing to link measured levels to terrain heights, a consideration deemed very important for accurate flood modeling.[1] Water level and salinity measurements were executed as part of an integral survey campaign that also included setting out Ground Control Points and Benchmarks, RTK-GNSS River bathymetry profile measurements, UAV (Drone) LiDAR Survey and UAV (Drone) Photogrammetry Survey.[2] OpenMap Development Tanzania (OMDTZ) teamed with Resilience Academy partner Delft University of Technology (TU Delft) to investigate if a new low-cost, dual-frequency GNSS receiver could be deployed for collecting very precise geographic position data for river cross-section surveys.[3] OMDTZ deployed two units that use the real-time kinematic (RTK) mode of the new, low-cost hardware that are able to provide centimeter precise surveys.[3] A team of 6 people (4 mappers and 2 technicians) was deployed to the field equipped with an Android smartphone with Open Data Kit (ODK) installed for data collection of Msimbazi River cross-sections.[3]

Implementation Details

The entire survey campaign including the water level logger installation took place from 14th until 20th of February 2019, with only the retrieval of the water level logger done after this period.[1] The German International Cooperation Agency (GIZ) worked with OpenMap Development Tanzania (OMDTZ) and Dutch knowledge institute Deltares to collect cross-section surveys of the Msimbazi River, extending an existing flood model for the Lower Msimbazi to include a much larger upstream portion of the river.[3] In collaboration with Deltares and with funding from GIZ, OMDTZ collected accurate and precise river cross-section surveys of the Msimbazi River using an innovative, low-cost technique developed by the Resilience Academy and OMDTZ.[3] OMDTZ developed a hydrological data collection protocol for ODK with Deltares, and carried out their first field survey with Deltares associates Bobby Russell and Hessel Winsemius, both of whom were experienced in hydrological surveys.[3] This first field exercise enabled OMDTZ to refine methods and safety precautions, after which the team was able to scale up and rapidly collect over 80 cross-sections of the river.[3]

Benefits and Impacts

The OMDTZ survey of river cross-sections and hydraulic structures along the Msimbazi River supported the creation of a comprehensive hydraulic model of the area that has led to the development of a more realistic flood hazard map of the most vulnerable areas.[3] This improved flood modeling capability addressed critical information gaps in the Msimbazi River Basin, which is located in Dar es Salaam Region of Tanzania, begins in Kisarawe ward, Kisarawe District and eventually drains into Zanzibar Channel at the border of Upanga West ward of Ilala MC and Hananasif ward of Kinondoni MC.[8] The 35-kilometer river system had been experiencing increasingly severe flooding over the past decade, with major flood events experienced in seven out of the last 10 years.[8][9]

Climate Adaptation Relevance

This monitoring and surveying approach directly addressed extreme precipitation and flooding hazards in the Msimbazi Basin, where the middle and lower portions had been experiencing frequent, severe flooding at least twice a year during every rainy season.[9] The comprehensive hydraulic modeling enabled by the water level logger data and associated surveys provided essential information for understanding flood dynamics in this economically important and flood-prone area. The Government of Tanzania, with a $200 million credit from the World Bank Group's International Development Association (IDA), established the Msimbazi Basin Development Project (2022-2028) to strengthen flood resilience and integrate urban development efforts in this area of Dar es Salaam.[9]

Sources