An emphasis is placed on the importance of understanding the processes responsible for resistance to flow and on the necessity of critically reviewing the assumptions and limitations associated with the methods that are commonly adopted to evaluate resistance to flow in gravel-bed rivers.A commonly applied technique is first presented for estimating the local effective boundary roughness, ks, by the use of data from a vertical velocity profile. Then methods of estimating bulk measures of resistance to flow in a river reach are outlined. Resistance equations in terms of the friction-factor parameter, [Formula: see text],are classified into three main types: dimensional power equations, nondimensional power equations, and nondimensional semilogarithmic equations. The results of seven independent studies are considered when recommending tentative equations for each of the three defined classes of resistance equations. The bulk flow equations are considered to be applicable for the case where d/D50 is greater than 10, there is no bed-load transport, and the flows are in-bank flows. Finally, a brief summary of the problems of estimating resistance to flow for an ice-covered channel is presented. Key words: resistance, flow, hydraulics, rivers, gravel-bed, velocity, friction factor, equations, Manning, Keulegan, classification.
A geochemical field study was conducted on the municipal aquifer in Fredericton, New Brunswick, Canada to determine the cause of increased manganese levels, from 0.02 mg/1 to about 1.0 mg/1 over a 34‐year period, in three of five production wells. The source of water for each of the five production wells has been determined to be infiltrated river water or precipitation, or a mixture of these sources. Wells that are predominately withdrawing infiltrated river water have corresponding high manganese concentrations, and redox potential data indicate that manganese tends to be in the aqueous form Mn2+. Geochemical modeling further suggests that the ground water is undersaturated with several common manganese minerals, while remaining supersaturated with iron oxide‐hydroxide minerals. The primary cause of the temporal increase in manganese concentrations is attributed to increased dissolved organic carbon introduced to the aquifer as a result of the escalating contribution of river water to the aquifer with time. Oxidation of organic matter proceeds in a ground‐water environment, as dissolved oxygen is depleted, by utilizing manganese oxides as electron acceptors.
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