A dam-breach erosion model: I. Formulation

This paper, Part I in a series of two, develops a mathematical model for earthern dam breach erosion. This model constitutes an extension of the Breach Erosion of Earthfill Dams (BEED) model developed by Singh and Scarlatos (1987). Two aspects are emphasized: the evolution of the dam breach, and the subsequent flood and sediment routing. Simulation of dam breach evolution is based on hydrologic, geometric and geotechnic considerations. Einstein-Brown and Bagnold equations are utilized to compute the rate of erosion in the breached section. A water routing scheme, based on a modified version of the Muskingum method to simulate flow exchange between channel and floodplains, is used to route the resulting breach hydrograph. A sediment routing scheme based on the Muskingum method, modified to simulate deposition in floodplains, and deposition and scouring in the channel, is utilized to route the breach sediment graph. In Part II, the model is tested against historical dam failures, and an analysis is made to determine its sensitivity to various parameters.     

Traditional Management Systems, Poverty and Change in the Arid Zone Fisheries of Northern Nigeria

This paper, based on fieldwork results, explores traditional management systems (TMS) in the arid zone fisheries of north-eastern Nigeria with particular reference to their impact on rural poverty. The first section provides a historical background by tracing the evolution of the TMS since the nineteenth century, with reference to government policy on fisheries management and poverty alleviation. The second gives an overview of TMS, including definitions, distribution, principal objectives, regulatory mechanisms and the impact of TMS on the performance of the fisheries and on the livelihoods of rural people. The third considers the perceptions and attitudes of the fishing communities with regards to the fisheries and TMS. The paper concludes, paradoxically, that while TMS provide a basis for the sustainable livelihoods of many fishing people, they also reflect and enforce the social positions of the rich and powerful members of society who oversee them, at the expense of the poor. In the future, poverty alleviation in fisheries will need to incorporate both sectoral and non-sectoral strategies – dealing with the existing 'paradox of TMS' by encouraging appropriate institutional changes and community development, and recognizing the importance of employment creation in other sectors of the economy as a source of alternative income.     

Een gebrekkig bankwezen

and now remains, That we find out the cause of this effect; Or, rather say, the cause of this defect. For this effect, defective, comes by cause.