Abstract ID
biodiv25
Type
Oral
Theme
biodiv
Full title
Environmental flows and wetland restoration in the Lower Zambezi River basin: progress and prospects
Abstract text
The Lower Zambezi basin supports nearly 4 million people and features the Zambezi Delta, Mozambique’s
premier Wetland of International Importance under the Ramsar Convention. Over the past century,
hydropower and infrastructure projects have substantially altered hydrological patterns and processes in the
lower Zambezi basin and delta, reducing ecosystem services, rural livelihoods, and biodiversity in the system.
A new partnership between Mozambique water management authorities, dam operators, development planning
authorities, research institutions, and conservation NGOs was established to assess the opportunities and
constraints for implementing environmental flow releases (EFRs) to restore the ecological health of the river
basin and key wetlands. A preliminary environmental flow process, building on more than a decade of
bio-physical and socio-economic research, was undertaken to identify potential conflicts/tradeoffs among water
users/water use concerns in the Zambezi Delta with respect to EFRs (flood-related small-scale agriculture,
commercial large-scale agriculture, estuarine ecology, coastal fisheries, freshwater fisheries, livestock, large
mammals, waterbirds, floodplain vegetation, invasive vegetation, natural resource utilization, water quality,
groundwater recharge/water supply, in-channel navigation, settlement patterns, human health) and to explore the
potential for improving delta conditions through EFRs from Cahora Bassa Dam. The low capacity to inflow
ratio (0.67) for Cahora Bassa (mean annual inflows ~77.1 Bcm and live storage capacity at normal maximum
operating level is 51.7 Bcm) forces late dry season water spillage most years to protect the dam wall, according
to a design flood rule curve. Simulation modeling to assess hydrological feasibility of EFRs indicates that
immediate improvement in the delta flow regime could be made with almost no impact on hydropower
production by redistributing those outflows to generate early wet season EFRs that also provide improved
storage capacity to attenuate large, potentially damaging floods (especially when downstream tributaries are in
peak discharge). For example, a 2-week discharge of 4500 cms in December could be achieved in 95.6% of all
years with 97.3% firm power reliability and 99.6% of baseline energy production, and a 4-week discharge of
this magnitude and timing could be achieved with 96.7% firm power commitment and 99.2% of baseline energy
production. Ongoing steps in the operator-driven process aim to (1) engage stakeholders in consensus-building
for EFRs through information exchange and stakeholder education; (2) define measurable objectives and
indicators and prepare initial EFR recommendations in a workshop setting; (3) implement an effective flood
forecasting and warning system for the reservoir and downstream tributaries; (4) establish a robust monitoring
and data collection program (hydrological, biophysical, socio-economic); (5) make water release experiments;
(6) monitor and evaluate releases for adaptive management; (7) define new EFRs as appropriate in follow-up
workshops. EFRs are being closely linked to integrated river basin development planning and protected area
management.
Submission date
2009-10-05
Keywords
land use, flood pulse, flood protection, consensus-building, monitoring, adaptive management
Will be submitting paper?
Yes