4Definition of “minor stream” and “Strahler system”

4 Definition of “minor stream” and “Strahler system”

4 Definition of “minor stream” and “Strahler system”

(1) In this regulation, minor stream means—

(a) a stream for which the location is specified in the hydro line spatial data and that has the following characteristics—

(i) is identified as a first or second order stream under the Strahler system,

(ii) does not maintain a visible flow occurring on a continuous basis, or that would occur if there were no artificial extractions of water or obstruction, of flow upstream,

(iii) does not carry flows emanating from a third or higher order stream under the Strahler system, or

(b) a stream for which the location is not specified in the hydro line spatial data.

(2) A stream is specified in the hydro line spatial data if the stream is identified as a watercourse, however described, in accordance with the legend or terms of the hydro line spatial data.

(3) The method of determining the stream order of a minor stream is the Strahler system.

(4) The Strahler system is as follows—

(a) a watercourse with no other watercourses flowing into the watercourse is classed as a first order stream,

(b) if 2 streams join of different orders, the resulting stream is the same order as the higher order of the 2 streams,

(c) if 2 streams join of the same order, the resulting stream is the order higher than the order of the 2 streams.

Example—

In the diagram below—

(a) if 2 first order streams join, the stream becomes a second order stream (2), and

(b) if a second order stream is joined by a first order stream, the second order stream remains a second order stream, and

(c) if 2 second order streams join, both second order streams form a third order stream (3), and

(d) if a third order stream is joined by a first or second order stream, the third order stream remains a third order stream, and

(e) if 2 third order streams join, both third order streams form a fourth order stream.