The control of anopheline breeding in river beds

Abstract

Abstract The preliminary experiments referred to in this paper, have been carried out with the object of ascertaining practical engineering measures for mass reduction of anopheline breeding in river beds. Sections of the Badulla Oya were selected and a number of devices tried out for reducing pooling along the sandy stretches of the river, and in draining and sealing cavities and permanent pools in the rock and boulder bed of the upper reaches. The experimental work so far carried out has given very encouraging results ; and, with the knowledge gained, it is hoped during the coming year to extend the sections under treatment and to modify the methods where possibilities for improvement have been indicated. Arrangements have been made to extend the experimental work to sections of rivers in other localities where additional devices will be tried out, particularly in connection with the control of channels in sand-bottomed rivers by the use of spur dikes alone, by spur dikes of other types, and with the aid of other materials. In order that work of this nature may be carried out upon an extensive scale, it is essential that simplicity of construction be observed and that the cost of such works shall not be prohibitive. It is necessary that a thorough inspection should be made of the sections to be taken up and the clearing of debris, fallen trees, etc., taken in hand without delay, as until this is done a final survey cannot be made. The importance of primary clearing cannot be over-estimated, as a considerable amount of the pooling, particularly in the tributaries, is due to this cause alone, and in many instances nothing more is necessary to permit the river carrying out its natural functions. The draining of pools cannot always be effected economically, but when possible, the water area should be reduced by drainage, preparatory to filling and sealing. The destruction of islands, where these interfere with natural flow conditions, should where possible be done by the flood waters, the islands being scored by narrow channels to encourage erosion. Back bays formed by the side tracking of flood waters, may in many instances be reclaimed by spur dikes and specially strutted closure fences. The eradication of malaria by any known means is often a protracted and difficult problem requiring patience and perseverance, but so long as temporary measures constitute the chief method of control in river beds little permanent improvement can be expected in the malaria conditions in the vicinity of rivers.