Hydrology and the functioning of seasonal wetland aquaculture-agriculture systems (Fingerponds) at the shores of Lake Victoria, Kenya

Experimental seasonal wetland-based integrated aquaculture-agriculture systems called 'Fingerponds' were established at two sites (Nyangera and Kusa villages) at the shores of Lake Victoria in Kenya to enhance the wetland fishery potential. This paper examines the hydrological characteristics of Fingerponds. In Fingerponds' design, the water supply is un-regulated and the water balance is maintained by natural losses and gains. At the beginning of the season, flood events are critically important for the initial water supply to the ponds. During their functional period (which lasted for about 6 months into the dry season after flood recession), precipitation accounted for nearly 90% of the total water gains while seepage and evaporation contributed an average of 30-70% of the losses, respectively. Seasonal pond water budgets indicated that the losses outweighed the gains leading to a progressive decline of water depth during the dry season. A prediction of the effect of pond volume and weather conditions on the functional period for fish production was carried out using a dynamic simulation model. The results indicated that the culture period can be extended by 2.5 months by deepening the ponds to an average depth of 1.5 m: this would increase the overall fish harvest. Drier weather accelerated losses and shortened the culture period by 1-2 months.