Since 2015 the NGOWP has systematically explored the major rivers that sustain the Okavango delta namely the Cuito, Cuanavale, Cubango and Cuando. This entailed land-based expeditions to rediscover the river sources in the highlands of Angola followed by mekoro (traditional dugout canoes) expeditions all the way to the rivers’ ends whilst recording data on biodiversity, ecosystem health and socioeconomics.
The team soon recognised the importance of what has now been termed the Okavango-Zambezi Water Tower, a giant pile of Kalahari sand rising to 1.8km with a footprint larger than Greece. Ample annual rainfall over this water tower (to learn more about water towers in Africa click here) percolates into the sand to be discharged slowly and consistently into the rivers that flow from it. The Okavango delta would not exist without this steady recharge of water, yet in the face of economic development and climate change, water flows require careful monitoring in order to predict adverse changes in the hydrological functioning of these rivers – and ultimately the continued livelihoods of people and wildlife downstream.
Previous attempts at hydrological monitoring of these rivers have largely been hampered by war, extreme inaccessibility and a lack of robust technology. Thus, hydrological models lack the data that are required to inform decision makers on how to best manage the water. For instance, how much water can be abstracted from the rivers before the Okavango delta is negatively affected? What impacts will new dams have on people living down river? Furthermore, such monitoring serves as an early warning for potential floods, detects changes in water quality and improves our general understanding of river hydrology and ecosystem functioning.
Hydrological Monitoring Plan
Through exhaustive consultation, workshops and symposiums with relevant stakeholders, experts and institutions, the NGOWP and its partners devised a hydrological monitoring plan that records water discharge, water quality and climate at several strategic locations throughout the Okavango Basin.
These solar powered stations are deployed on bridges and take hourly readings that are communicated via satellite link to the end user in real time.
Water discharge is monitored by an RQ30. This cutting-edge device is suspended below the bridge and calculates river discharge from water level and velocity using pulse radar signal and doppler frequency shift respectively. To calibrate the RQ30, the ‘wet’ and ‘dry’ riverbed profiles are first measured using an acoustic doppler current profiler and a laser distance measurer respectively and uploaded to the device.
Long term monitoring of water quality is more challenging, as it requires a logging device to be permanently submerged in the river. We chose the InSitu Aquatroll 600 multiparameter sonde measuring pH, oxygen reduction potential, rugged dissolved oxygen, turbidity, conductivity and temperature, all of which are indicators of potential changes in water quality. The device requires periodic maintenance and re-calibration and thus has to be accessible from the top of the bridge as well as remain safe from floating debris.
We solved this by installing the device in a perforated pipe mounted on a down-current bridge pillar on a closed-loop pulley system.
To monitor rainfall, wind, temperature, barometric pressure and humidity, we installed a Vaisala WXT530. This compact device does not have moving parts and thus requires less maintenance than conventional weather stations.
To power the station we used an 80W solar panel secured in a vandal proof housing and the data logger, communication device and battery were housed in a bulletproof enclosure.
The resultant monitoring station was assembled and programmed by Campbell Scientific Africa.
Divundu Bridge Installation
Recently, the team installed the first station at Divundu Bridge in Namibia. Team members included Rainer von Brandis and Götz Neef (NGOWP); Leonard van der Merwe (Campbell Scientific Africa); Allan Craw and Arno Janse van Rensburg (Access and Rigging Services); Victor Lehmann and Guillio Kröhne (Namibian Ministry of Agriculture, Water and Forestry) and Christoph Lohe and Stephanus Markgraff (Water Associates of Namibia). Together the team successfully deployed and configured the monitoring station over a period of 5 days.
Once verified, analysed and modelled by expert hydrologists, the data will be used by the governments of Angola, Botswana and Namibia and their various partners and advisors (OKACOM, KAZA, EU, GIZ, KFW, UNEP, USAID, World Bank, WWF, CI, TNC, etc) as a decision support tool for sustainable development, wise water management and early flood warning. Furthermore, any interested party will be able to access the real-time readings and data visualisations by following this link. It is important to note that the data and visualisations portrayed in this link are unverified.
Neither the NGOWP nor any of its employees, contractors or subcontractors make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any data portrayed.