January 12, 2018

Water and sediment: news from the Mara Wetland, Tanzania

Posted by larryohanlon

By Francesco Bregoli 

Where the Mara River leaves the Serengeti National Park, Tanzania, a meandering reach expands to form a delta and a wide wetland before flowing into Lake Victoria. The wilderness of Serengeti dissolves into rural areas that envelope the swamps (Fig 1), but still the riverine system provides unique water resources and essential ecosystem services that should be preserved.

Fig. 1 Aerial photo made with an UAV flight showing crops and grazing lands replacing the riparian and floodplain vegetation on the north bank of the Upper Mara River Wetland. Picture by Francesco Bregoli


Water and sediment are the raw materials necessary to build up the wetland habitat and are vectors of nutrients feeding the ecosystem. When their natural equilibrium is broken, the habitat morphology is altered and the ecosystem health is likely jeopardized. Previous studies report an increment of sediment supply to the wetland due to increasing deforestation, farming and grazing activities along the basin. New river structures are planned and the river management will become an important challenge for the area.

Motivated by the great opportunity to picture the current condition in a changing environment, I went for a three weeks mission on the Mara Wetland to gather data on morphology, water discharge and sediment transport. I built up the field data collection from two past missions of Paolo Paron and Ken Irvine, when they used drones to collect data on hydrology and ecosystems. The data are important to understand the current configuration and to model the future evolution of the wetland under different scenarios of climate, water use and land use changes along the river basin. The measurements will support an analysis of the water and sediment balance within the area of the Lower Mara floodplain. Furthermore the model will serve as a tool to improve the water resources and land use management in order to prevent the deterioration of the Mara wetland habitat and ecosystem.

Fig. 2 Drone selfie of Francesco operating with the LVBO team on the South West bank of the Lower Mara Wetland. During the dry season, grazing is intense on the floodplain. Picture by Francesco Bregoli

During the mission I deployed UAV flights to observe areas otherwise unattainable from the ground and to represent the wetland morphology features at high resolution (Fig 2 and 3). I measured water discharges with an ADCP (Fig 4) in several key channels of the network, cruised the wetland to map the bed topography with a sonar and gathered suspended sediments samples.

Fig. 3 Example of orthophoto taken at the Upper Mara Wetland with a DJI Phantom Pro 4 from a height of 200 m with a resulting resolution of 5 cm/pixel. Photo by Francesco Bregoli

I realised that even in remote areas you are never alone. Thanks to the support of BirdLife International I had the chance to talk with people of the local communities. In many cases I have noted the awareness that the organizations are creating among the communities: I have found them curious, participative and willing to preserve their territories. I have witnessed their perception of the importance of the ecosystem services the wetland provide them. Still, there is a number of ongoing human activities that might modify the environment and particularly the river network: riparian vegetation burning to create new croplands and to provide fisherman access to the river, livestock paths and wades as well as banks opening for land irrigation are among the reasons of natural levees destruction and therefore river bifurcation or deviation.

Fig. 4 Measuring the flow with an OTT Qliner2 in the main stream of the Upper Mara River Wetland. Here the river is rich in suspended sediments. Riparian vegetation is absent. Picture by Francesco Bregoli

The knowledge to which extent the human actions change the natural water-sediment balance of this delicate ecosystems will be the object of further analysis of my research.


Francesco Bregoli is a researcher of the River Basin Development chair group of IHE Delft Institute for Water Education. His research activity is funded by IHE Delft and EU through the Experienced Water Postdoc Fellowship COFUND Programme.
IHE Delft partnered for this mission with the Lake Victoria Basin Water Board (LVBWB) of Tanzania and BirdLife International.
LVBWB is the authority in charge of monitoring the water resources and the water allocation of the Tanzanian part of the Mara basin and provided support to IHE Delft for water discharge measurement and sediment analysis.
With its presence on the territory, Birdlife International is doing an essential job of creating awareness on water resources use among the local users. Birdlife International introduced IHE Delft to the local communities along the Mara Wetland and provided support for the field work.