ISO TR 9210:2017 pdf free.Hydrometry一Measurement in meandering river and in streams with unstable boundaries.
This document provides guidelines for discharge measurements in meandering and braided rivers, and from bridges, following the provisions of ISO 748.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 772. Hydrometry — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— I EC Electroped Ia: available at http://www.electropedia.org/
3.1 alluvial river river, which flows through alluvium, formed from its own deposits
Note I to entry: The sediment carried by an alluvial river, except for the wash load, is similar to that in the bed.
3.2 braided river river characterized by a wide and shallow open channel, in which flow passes through a number of small-interlaced channels separated by shoals
Note ito entry: Frequently, there is little or no erosion of the main banks of a braided river.
Note 2 to entry: Generally, there is little or no meandering of the main channel of a braided river, but meandering in the minor channels is usual.
3.3 meandering river channel following a sinuous path, characterized by curved flow leading to bank erosion alternating with shoaling
4 Site selection in rivers
However, when the flow directions during flood and low flow seasons are very different, it is permissible to suitably adjust the orientation of gauging section during that season, taking into account the requirements in ISO 748:2007, 5.1 a) and b).
Iso 748:2007, 5.1 b) further states that the accuracy of the determination of discharge is increased if the flow directions for all points on any vertical are parallel to one another, and at right angles to the measurement section.
iSO 748:2007, 5.1 c) recommends that the bed and the margins of the channels should be stable and well-defined at alt stages of flow in order to facilitate accurate measurement of the cross-section, and to ensure uniformity of conditions during and between discharge measurements.
At a measuring site, even if properly located to satisfy these requirements during flood season, the flow direction can change appreciably during low water season. As far as possible, the basic stream gauging section should not be changed. However, when the flow directions during flood and low water seasons are very different, it is permissible to suitably adjust the orientation of gauging section during the low water season, taking into account the requirements in ISO 748:2007, 5.1 a) and b).
5 Site selection in rivers with relatively stable meanders
in alluvial rivers, the course over long reaches is sometimes comprised of one meander followed by another. Then, finding a sufficiently long straight reach becomes difficult.
In a bend, transverse flow develops, and the resultant direction and velocity of flow are composed of the net effect of normal and transverse flows. The distribution of velocities and depths across the section also becomes extremely heterogeneous. In the transitions between successive meanders, the river course is relatively straight over a short reach. The cross-sections are more uniform and better defined than those in the bends are. A transition therefore provides better site conditions for a gauging station. When a straight reach over a sufficiently long distance is not available, the best alternative is therefore to select a gauging site in the transition between successive bends.
The important factors that affect the accuracy of the discharge measurement in meandering rivers are the scouring, silting and the change in flow direction at the discharge measuring section. The velocity measured at each point should be corrected for angle using a direction-measuring current meter.ISO TR 9210 pdf free download.