THE PERFORMANCE OF a two-stage river channel is examined from a combination of collected field data on the River Roding and a hydraulic model study. Particular attention is paid to the vegetation on the upper channel berm, including its seasonal effect on hydraulic resistance and the problem of channel maintenance. Recommendations are made with respect to (a) increasing the present capacity of the River Roding, and (b) the future design of two-stage flood channels intended to meet stringent environmental standards.

Aun cuando son, relativamente, incompletas nuestras observaciones sobre este tema debido a la escasez de material patológico y a la condición en que el mismo llegó para su estudio, juzgamos conveniente una descripción para animar a otros observadores nuestros a fin de completar el cuadro anatómico. Otra razón más que no simpele a publicar estos apuntes es el de comparar nunestros resultados con los de varios investigadores y notar sus analogías.

Sir Charles such rivers as the Volga and the Don was almost impracticable, H a r t b . because the slopes opposite those mouths were extremely flat ; the littoral current was almost imperceptible, and the direction of the wind unfavourable to successful treatment. Similar allegations might be made with regard to many tidal rivers entering tidal seas. The river Adour, for example, had hitherto been unamenable to improvement, and the Hooghly would be very difficult to improve, whereas the Thames below London Bridge, and the Scheldt below Antwerp, for the time being a t least, needed no serious improvement, and the same thing might be said with regard to other rivers. It woeld occupy too much time to discuss the relative advantages and disadvantages of tidal and tideless rivers, from Downloaded by [] on [11/09/16]. Copyright © ICE Publishing, all rights reserved. DISCUSSION ON NON-TIDAL RIVERS. [Minutes ofSir Charles there was an increased length in the river below Rome of 45 per Hart'ey* cent., owing to its sinuosities, and that he knew of no tidal valley subject to the disadvantages both of navigation and drainage which that implied. But the length of the Seine between Rouen and the estuary was about twice the distance in a straight line.H e fully agreed with the Author that in river-engineering the fundamental conditions to be studied were at the outfall, but he could not' concur in the opinion that with regard to the Tiher the improvement of its outfall would be very difficult, if not impracticable, for want of sufficient water at ordinary times to keep it clear. On the contrary, remembering the advantages of a comparatively steep slope in front of the mouths, the slow advance of the delta, and observing the direction of the currents, and the comparatively large proportion of the dry-weather flow to the mean flow, he thought that the improvement of the outfall, and the regulation of the lower part of the river would not be very difficult or beyond the ordinary skill of the engineer. Downloaded by [] on [11/09/16].

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