ISO INTERNATIONAL STANDARD 4374 Second edition 1990-03-15 Liguid flow measurement in open channels Round-nose horizontal broad-crested weirs Mesure de debit des liquides dans les canaux decouverts -- Deversoirs horizontaux aseuilépaisarrondi Reference number ISO 4374 : 1990 (E) Not for Resale ISO 4374 :1990 (E) Foreword Iso (the International Organization for Standardization) is a worldwide federation of national standards bodies (Iso member bodies). The work of preparing International Standards is normally carried out through iso technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with Iso, also take part in the work. ISo collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circuiated to the member bodies for approval before their acceptance as International Standards by the Iso Council. They are approved in accordance with Iso procedures requiring at least 75 % approval by the member bodies voting. International Standard iSO 4374 was prepared by Technical Committee ISO/TC 113, Measurement of liquid flow in open channels. This second edition cancels and replaces the first edition (ISO 4374 : 1982), of which it constitutes a technical revision. Annexes A, B and C form an integral part of this International Standard. NOTE - Guidelines for the selection of weirs and flumes for the measurement of the discharge of water in open channels are given in IS0 8368 : 1985, Liquid flow measurement in open channels - Guidelines for the selection of flow gauging structures. ISO1990 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing fromthepublisher. International Organization for Standardization Case postale 56 . CH-1211 Geneve 20 . Switzerland Printed in Switzerland Noreproductionornetworking permited without license fromIHS Not for Resale ISO4374:1990 (E) INTERNATIONAL STANDARD Liquid flow measurement in open channels --- Round-nose horizontal broad-crested weirs 1 Scope 4.1.2 A preliminary study shall be made of the physical and hydraulic features of the proposed site, to check that it con- 1.1 This International Standard deals with the measurement forms (or can be made to conform) to the requirements of flow in rivers and artificial channels under steady flow con- necessary for measurement of discharge by the weir. Particular ditions using round-nose horizontal broad-crested weirs (see attention should be paid to the following features in selecting figures 1 and 2). the site: a) the adequacy of the length of channel of regular cross 1.2 The flow conditions considered are limited to steady section available (see 4.2.2.2); flows which are uniquely dependent on the upstream head. Drowned flows, which depend on downstream as well as b) the uniformity of the existing velocity distribution (see upstream levels, are not covered by this International Standard. annex B); c) the avoidance of a steep channel (but see 4.2.2.6); 1.3 The round-nose horizontal broad-crested weir has a good discharge range and modular limit and is appropriate for use in d) the effects of any increased upstream water level due to small- and medium-sized installations. It is particularly robust the measuring structure; and insensitive to minor damage. e) the conditions downstream (including influences such as tides, confluences with other streams, sluice gates, mill 2 Normative references dams and other controlling features which might cause drowning); The following standards contain provisions which, through reference in this text, constitute provisions of this International f) the imperme