Advances in restoring and enhancing ecosystem services in vulnerable lower Tana Delta and coastal communities: amplifying local voices through transdisciplinary science

With an average discharge of 100 m³s^-1, the Tana River is Kenya’s most important river, entering the Indian Ocean via the 160,000 ha Tana Delta Ramsar site, also an Important Bird Area and a biodiversity hotspot for threatened plant and animal species. Its floodplains and mangroves are key nursery areas for a coastal fisheries, both semi-industrial targeting shrimp and artisanal for a wide range of species. 

Since the 1960s, five upstream hydropower dams have reduced peak discharge of the Tana by 30% and a larger dam, capable of storing up to 2 years of the river’s flow, has been planned. The reduced discharge of the Tana has resulted in less flooding of the Delta, exacerbating resource conflicts between sedentary farmers and mobile livestock keepers. Moreover, the fertile floodplains were targeted for large-scale irrigated agriculture (including by interbasin transfer) and its terraces for biofuel production, adding threats to local livelihoods.  

In order to favour tidal rice cultivation in the lower reaches of the delta, just upstream of the mangrove systems, local communities have blocked the Kalota Brook, a major section of the river mouth, dominant prior to the 20^th century. Though these interventions have maintained fresh water in the main riverbed, they have interfered with land-building processes downstream of Kalota and resulted in increased saltwater intrusion and erosion as well as a decline of biodiversity, biological productivity and nursery functions in the central part of the delta. In spite of repeated and expensive engineering attempts, the blockage of Kalota Brook has been unsuccessful, circumvented by new and increasingly deep tidal channels while in turn the central river mouth has been widening, allowing more and more seawater to enter compounded by Sea Level Rise.

Through a participatory science approach developed in DIDEM project, key local observers have been involved in the analysis of the hydrodynamics of the Delta and its impact on its biodiversity values and ecosystem service delivery to vulnerable groups. 

Methods applied include biodiversity surveys, hydrodynamic modelling of impacts of the changes on local agro-ecological systems, geomorphological and palaeo-ecological analysis (through coring), groundwater studies, focus group discussions, in depth interviews and commented field visits, stakeholder feedback and discussion workshops;  the outcomes of which have been communicated at policy and decision-maker level, both locally and nationally.

In addition to the participatory research and monitoring activities, a communication strategy was developed for information sharing and awareness building. Communication products include a documentary, a science festival during World Wetlands Day celebrations, a traveling exhibition, debates at several levels, a stakeholder peace dialogue, as well as numerous popular publications targeting schoolchildren and civil society. 

Our findings suggest that, in contrast to traditional compartmented land use planning, deltas require an adaptive and flexible multi-user approach adapted to climatic and river discharge conditions. In collaboration with the stakeholders, we propose a nature-based solution for Kalota Brook. This would allow a dynamic environmental flow, calibrated in relation to the critical equinox tides, to the central river mouth sufficient to maintain and enhance the land-building mangrove systems.