Model and Prototype Results for a Sinuous Two‐Stage River‐Channel Design

Abstract

A relocated length of the River Blackwater in Hampshire, UK, has been designed and constructed as a doubly‐sinuous, two‐stage channel. This has been established as a field test site with water level and discharge recording equipment for an ongoing analysis of its hydraulic and ecological performance. Preliminary hydraulic data, which were collected from the site, are analysed and compared with data from two hydraulic models which were built to the same design but at different scales. Results from the prototype, the 1/5, and 1/25 scale models are examined for scaling relationships and scale effects. The small‐scale model was then reconstructed with a 2:1 vertical‐scale exaggeration, and the results were assessed against the others. Methods for the selection of appropriate surface roughness for small‐scale river models are discussed.

An improved method for roughening floodplains on physical river models

“…However the earlier 1 to 5 scale model of the Blackwater had shown all these features, when roughened in a different way, as described above, and these were in agreement with measurements and observations made on the prototype -Sellin et al [18].…”

“…The overall friction factor f, corresponds to the scaled Darcy Weisbach friction factor. = WJifl-p-C, +1 (18) Fig. 7.…”

“…This is dura ble and watertight but too smooth to model floodplain rough nesses found in nature. A specific river model of the two-stage channel on the River Blackwater in Hampshire, UK, ( Sellin, Wil son and Naish [18]) had already shown that a large amount of roughening was required for a floodplain built to such a large scale (1/5 prototype size). A number of methods of roughening floodplains have been used in physical river models.…”

Using an acoustic Doppler current profiler in a small river

“…This section illustrates how the above techniques and equipment have been applied to a 300 m reach of a two‐stage, double meandering channel of the River Blackwater, Hampshire, UK (Fig. 5), which previously had been studied by Lambert & Sellin (1996), Naish & Sellin (1996), Sellin et al (2001), Sellin & van Beesten (2002) and Sellin & van Beesten (2004). The channel was altered and re‐engineered due to a major road construction nearby and the hundred‐year flood design capacity of the channel was 4.3 m 3 /s with a bank full capacity of the main channel of 1.5 m 3 /s (Sellin & van Beesten 2004).…”