An ecologically useful classification of mean and near‐bed flows in streams and rivers

Abstract

I. Mean motion and near-bed flows in streams and rivers can be described using a classification derived from fairly simple field measurements. Our proposed classification is ecologically useful because it incorporates the combined effects of velocity, depth and substrate roughness to provide a means ot quantifying the flow regimes occurring within the microhabitats of stream benthos.2. Mean motion is characterized by the Reynolds number and the Froudc number. Both are easily calculated, and because they are dimensionless they provide a means of comparing flows at different sites.3. Five categories of near-bed flows (i.e. the flow microenvironments of stream benthos) arc recognized. Flow may be hydraulically smooth or hydraulically rough and the latter category is subdivided further into: chaotic flow, wake interference flow, isolated roughness flow and skimming flow. Hydraulically smooth flows occur in sections of a river bed with fine sediments (e.g. sands, muds and clays).overflat sheets of bedrock, or in association with the flat blades of submerged macrophytes. Hydraulically rough flows occur where the substrate elements are larger (e,g. pebbles, cobbles and boulders) and are a function of substrate roughness and the depth of flow relative to the height of the roughness elements. Chaotic flows and wake interference flows predominate in riffles whilst isolated roughness flows and skimming flows are more likely to be a feature of runs.4. Conventional stream sampling methods (e.g. the Surbcr and box or cylinder samplers) may collect across several different flow microhabitats. Our classification should enable different flow microenvironments to be recognized and so sampled more appropriately which, in turn, may reduce apparent clumping and the wide confidence intervals of benthic population estimates. Because our classification identifies 'patches' within the flow regime associated with the stream bed it enables stream ecologists to generate testable hypotheses regarding the distribution and abundance of benthic species in response to flow. 5. Our classification identifies spatial patterns in the flow regimes associ-

Effects of hydraulic conditions and larval size on the microdistribution of Hydrobiosidae (Trichoptera) in two New Zealand rivers

“…The use of water depth, velocity, and substrate size alone to describe flow conditions and conventional sampling tools such as Surber nets have been criticised for not adequately characterising the flow environments experienced by benthic invertebrates or for potentially collecting across several different flow micro-habitats (Nowell & Jumars 1984;Davis 1986;Davis & Barmuta 1989). Quinn & Hickey (1994) found that inferred shear velocity and boundary layer Re best described the abundance of several species of aquatic insects collected in Surber samples in two New Zealand rivers, but this was not evident for the Hydro- biosidae taxa examined in our study.…”

“…Median substrate size and roughness were 5.6 and 3.8, respectively, for the Tongariro River, and 6.3 and 7.1, respectively, for the Mangles River. Ninetypercentile values for Fr were < 1 and for Re were > 2000 indicating that the conditions sampled in both rivers were predominantly subcriticalturbulent (after Davis & Barmuta 1989). Median U*3 and Re* 3 were, respectively, 4.6 and 2604 in the Mangles River samples, and 5.2 and 1452 in the Tongariro River samples ( Table 2).…”

Zoobentos I Dnevne Oscilacije Vrbasa Iznad Banja Luke / Zoobentos and Daily Oscillations of Vrbas Upward Banja Luka

“…Promijenjeni hidrološki uslovi igraju važnu ulogu u prostornom rasporedu organizama (Lindström et Traaen, 1984;Statzner et al, 1988;Davis et Barmuta, 1989;Yong, 1992). Organizmi su suočeni sa periodima suše i poplave, koji se smjenjuju u nepravilnim dužim ili kraćim vremenskim odsječcima, što se odražava na sastav i strukturu njihovih biocenoza.…”

Зообентос Сане И Гомјенице На Ушћу У Сану

“…Велики утицај на дистрибуцију зообентоса имају хидролошки услови који владају дуж тока (Lindström et Traaen, 1984;Statzner et al, 1988;Davis et Barmuta, 1989;Yong, 1992). Основни ограничавајући фактор у текућицама је кретање воде (зависи од нагиба ријечног корита).…”