Arthur T. Ippen

Ecological Design of Irrigation Canals for Snail Control

The snail hosts of schistosomiasis have found ideal conditions for rapid colonization in many irrigation and drainage canal systems. By studying the hydrodynamic aspects of snail dislodgment it may be possible to devise a control method based on engineering the snails microenvironment. For Australorbis glabratus, a velocity exceeding 33 cm/sec at shell height produces a hydrodynamic drag force sufficient to dislodge the snail from its position on the solid boundary of a canal.

WAVE REFLECTION AND TRANSMISSION IN CHANNELS OF VARIABLE SECTION

The distribution of bed-load sand transport normal to the beach has been measured m a series of field experiments conducted in the surf zone at Fernandma Beach, Florida. Simultaneous measurements were made of the waves and water particle motion at various locations in the surf zone. The energy flux of the waves was resolved Into Its longshore component from the measured directional and energy spectra. It Is found that the bed-load transport is related to the depth of water and longshore energy flux. Insight into the mechanics of sediment transport is obtained by comparing the wave and water particle motion energy spectra, which give a direct measure of the kinetic and potential energy, at various locations in the surf zone. INTRODUCTION A meaningful field investigation of the sand transport processes m the surf zone requires the synoptic measurement of a number of hydrodynamic and sediment variables. Fairly complete and extensive data are required to evaluate the validity of various proposed sand transport relationships and the formulations of new relationships where necessary. This paper describes field experiments conducted m the surf zone at Fernandma Beach, located on the northeastern coast of Florida. The emphasis of this study was to obtain information concerning the distribution of bedload transport perpendicular to shore and the physical processes causing such movement. Sediment transport m the surf zone can be considered as being caused by a combination of shear stresses due to wave and current action. An attempt to correlate sediment transport with physical parameters then must include good wave and current measurements. The experiments were conducted from October, 1966 to May, 1967, a period that encompasses the more intense wave activity along this coast. The beach and nearshore bottom profile is typically a one or two bar system with a gentle slope of two to three per cent. The sand has a mean grain size of approximately 0.2 millimeters. The mean tidal range is 1.7 meters.A summary is given of the results of training sixteen rivers in an endeavour to increase bar depths for navigation. The bars are of simple crescent formation fed by littoral drift. Whilst the training works have improved conditions for navigation they have not resulted in any appreciable increase in bar depths. Despite the complex mechanisms involved in bar formation a consistent simple correlation is found to exist between channel and bar depths. This correlation seems to apply to all rivers and inlets with simple bar systems and extends over a range from a bar depth of two feet to 60 feet. The correlation holds for rivers elsewhere and-- with varying climates of exposure.