摘要:

AbstractAfter dry summers or drought, eucalypt forest soils at two sites in southeastern Australia developed hydrophobic or non‐wetting surface characteristics that reduced infiltration, measured using a sprinkling infiltrometer. At one site the development of hydrophobic conditions caused the rainfall to runoff conversion efficiency of a forested catchment to increase from 5 per cent to 15 per cent. Under non‐hydrophobic conditions at this site, grassland always generated more runoff than forest. However, one major rainfall‐runoff was recorded at a time of highly hydrophobic forest soil conditions and this storm generated greater runoff on the forested catchment than the grassland catchment.At the second site forest soils have naturally highly conductive surface layers because of a dense network of macropores and pathways for preferential flow. Hydrophobic conditions produced by drought caused soil water movement to be confined to only a few of the larger macropores exposed to surface ponded water. Even so, infiltration rates remained relatively high so that the impacts of hydrophobic soils were not translated into increased catchment runoff as at the first

ISSN:0885-6087    

DOI:10.1002/hyp.3360030302

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractKnowledge of groundwater seepage to and from lakes can be an important component of scientific investigations involving water and geochemical budgets. Measurements of groundwater seepage at Lake Anna, a man‐made lake in central Virginia, show that inflow to the lake occurs even under dry summer conditions. Seepage rates were found to be correlated with the elevation of the near‐shore water table, which responded rapidly to rainfall events in the fractured rock terrane in which Lake Anna is located. Seepage rates did not decline uniformly with distance offshore. This result contrasts with those for lakes underlain by relatively homogeneous porous media where measurements generally confirm the prediction that seepage rates drop off exponentially with distance from shore. The along shore variability of seepage rates in Lake Anna was related to a topographic index that is used to describe drainage from hillslopes. This suggests that seepage in impoundments such as Lake Anna may be strongly controlled by drainage pathways that pre‐date the

ISSN:0885-6087    

DOI:10.1002/hyp.3360030303

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractAnalysis of the bankfull cross‐sections of headwater streams in Ado‐Ekiti region of Southwestern Nigeria and their comparison with data from other tropical environments and temperate latitudes reveal that the channel capacities of streams in the humid tropics are relatively smaller than those of temperate regions, averaging 1.51 m2with a coefficient of variation of 87 per cent. This is attributed to the small stream discharge, the predominantly low and highly seasonal flows of the streams, the low shear stress of stream load, and the stabilizing and protective influence of riparian vegetation and surface incrustations. The chanel capacities of the urban streams (mean = 1.13m2) are about 47 per cent smaller than those of the natural streams (mean = 2.12 m2) in the same ecological zone. In terms of hydraulic efficiency, the urban streams also have relatively inefficient cross‐sections and larger width/depth ratios than their rural or natural counterparts. Resurveys of seventeen monumented cross‐sections reveal that while channel shoulder width increased by only 6 per cent over a one‐year period, channel depth and capacity decreased by 16 per cent and 4 per cent respectively; the observed decrease in channel size occurs entirely in the channel depth dimension. Thus the response of stream channels to the urbanization of small headwater catchments in the humid tropics is probably more of vertical accretion of channel bed and reduction in channel capacity rather than the widely‐reported anomalous enlargement of urban streams through channel widening. The rapid rate of channel aggradation is attributed to excessive rates of sediment production and delivery to streams in urbanized catchments in the humid tropics, rapid deposition of sediments during small runoff events and on the falling stage of storm hydrographs, and the inability of the streams to evacuate the sediments delivered to them despite the increased discharge and peak flow associated with urbanization. The low competence of the urban streams is attributed to the predominance of low flows, very gentle bed slopes, and most importantly the widespread dumping of refuse into the channels thereby reducing flow velocity and promoting backwater flooding, ponding, and sedimentation. The correlations between drainage basin area, a surrogate for stream discharge, and channel capacity are very strong for the rural watersheds, and the regression analysis indicates a tendency towards a steady‐state isometric relationship. Urban channels are, to a large extent, in disequilibrium with the urban hydrological state. However, spatial variations in the degree of urbanization of the catchments, and, therefore in runoff volume and velocity, exercise strong control on channel width, depth, and size. A model of the sequence of stream channel adjustment to the urbanization of small headwater catchments in the humid tropics

ISSN:0885-6087    

DOI:10.1002/hyp.3360030304

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractHorowitzet al.(in press) have reported a quality assurance study for metals for two continuous‐flow centrifuges commonly used for environmental applications in field situations. Their work is at an experimental level and avoids discussion of practical considerations involving portability, flow rates, maintenance, etc. In this paper we examine these practical considerations which should be included in application decision

ISSN:0885-6087    

DOI:10.1002/hyp.3360030305

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractReservoir release wave routing during 33 controlled reservoir releases, along 15 upland boulder bed river channel reaches, on five different regulated rivers were monitored to assess the importance of river channel roughness and reservoir release magnitude on reservoir release wave speeds. Wave speeds varied between 0.52 and 3.01 m s−1. Reservoir release wave translation, steepening, and attenuation occurred. With high channel roughness values reservoir release wave arrival speed is retarded in comparison to peak stage and wave steepening occurs, but with a reduction in channel roughness reservoir release wave front arrival is accelerated producing attentuation. The threshold between reservoir release wave front attenuation and steepening occurs at a pre‐release discharge/channel width of approximately 0.1, an index of channel roughness.The paper also demonstrates, via comparison of observed and calculated reservoir release wave speeds on the River Washburn, Yorkshire, the difficulty of accurately predicting flood wave movement in upland boulder bed channels using existing prediction equations. The calculated values, however, revealed systematic error with pre‐release discharge and reservoir release magnitude. Apparently the equations fail to account for the effects of high channel roughness together with pressure gradient forces, induced by rapid rates of stage change on the rising limb of reservoir releases. In order to accurately predict reservoir release wave movement in regulated rivers, this paper demonstrates that hydraulic studies need to be undertaken and pre‐release discharges prescribed to determine desired reservoir release wave routing behaviour. Manipulation of the reservoir release pattern at the dam alone, cannot dictate reservoir release wave front form downstream or wav

ISSN:0885-6087    

DOI:10.1002/hyp.3360030306

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe molecular weight (M. W.) distributions of iron and manganese species in dam water samples were investigated by use of gel filtration, while the ion‐exchangeable and non‐ion‐exchangeable fractions of these metals were also analysed by ion‐exchange chromatography. For the samples studied, more than 96 per cent of the manganese species present were found to be ion‐exchangeable, whilst less than 35 per cent of iron species were ion‐exchangeable. These results correlated with the finding that all the manganese species had molecular weights less than 700, but that the molecular weights of the iron species were mostly in excess of 5000. Electron paramagnetic resonance (EPR) spectroscopy has been used to support the finding that manganese is almost totally present in the form of simple aquated

ISSN:0885-6087    

DOI:10.1002/hyp.3360030307

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360030308

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360030309

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360030301

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY