摘要:

AbstractBenthic macroinvertebrates were examined over a two‐year period in nonregulated, regulated, and semiregulated reaches of the Clearwater River in northern Idaho. Macroinvertebrate communities in the nonregulated reach above Dworshak Reservoir were taxonomically diverse at all stations. In contrast, the macroinvertebrate community in the regulated reach of the North Fork of the Clearwater River (NFCR) was severely altered with high macroinvertebrate abundance and low taxa richness (2 to 8 taxa). Orthoclad chironomids dominated this reach composing between 68 and 99 per cent of total benthic invertebrate numbers. The mayflyEphemerella infrequenswas the only other macroinvertebrate to be abundant in the regulated reach. The major factors contributing to the simplified macroinvertebrate community are reduced habitat diversity, fluctuating water levels, altered thermal regime, and possibly an altered food supply. The effects of the dam were mitigated in the semiregulated Mainstem of the Clearwater River (MSCR) due to the merger of a nonregulated fork entering 2.5 km downstream from the dam. The macroinvertebrate community in the semiregulated MSCR was more complex than the regulated reach with a community structure resembling that found above the reservoi

ISSN:0886-9375    

DOI:10.1002/rrr.3450060102

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA full computer based investigation of the factors influencing the modelling of overbank flood discharges has been carried out. Several floods of differing magnitudes and peak curvatures were routed down regular channels using an implicit finite difference scheme and the influence of time and distance steps used for the numerical solution of the flow equations were investigated.Spillage over sharp crested weirs was assumed to satisfactorily simulate the overbank flood discharge; the importance of a correct estimation of the coefficient of discharge was also checked. It was shown that sensibly chosen values of the time step had little effect on the simulations. This was also true for the value of the coefficient of discharge when the sideweir flow was predominately drowned, but not for free flow conditions. It was also shown that close spacing of computational nodes was required at the onset of overbank flow to accurately simulate the overflow and also model the occurrence of large water level gradients.

ISSN:0886-9375    

DOI:10.1002/rrr.3450060103

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractChanges in montane meadow vegetation were examined in a previously ephemeral drainage that received flow augmentation as a mitigation measure for a transbasin diversion in southeastern Wyoming. After two years of elevated surface and groundwater levels, the herbaceous vegetation shifted toward more water‐tolerant species. Dry meadows became like moist meadows, moist meadows became more like moist‐wet meadows, and moist‐wet meadows became more like wet meadows. Sedge (Carexspp.) biomass increased from 337 to 456 g m−2in the wet meadows, while tufted hairgrass (Deschampsia cespitosa) biomass decreased from 18 to 3 g m−2in the moist‐wet meadows. Slimstem reedgrass (Calamagrostis neglecta) remained unchanged in the meadows with shallow standing water, but increased from 17 to 88 stems m−2in the dry meadows with an elevated water table. Bare ground also increased as much as 31 per cent in the meadows without a defined dra

ISSN:0886-9375    

DOI:10.1002/rrr.3450060104

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe potamodromous smallscale redfin minnow (Pseudobarbus asper) spawned in the riffle areas of the regulated Groot River, the major tributary of the Gamtoos River system, during controlled releases of water from Beervlei Dam. Water had been released at irregular intervals from this flood control dam solely for irrigating agricultural lands. Flushing flows removed accumulated salts from riverine pools and were followed by reduced flows which initiated spawning of the minnow species. Developing embryos ofP. asperwere found in the riffle zone of the main river channel during the water releases. Ripe‐running males were located under the boulders in the riffles. Several developing embryos ofLabeo umbratuswere found with theP. aspereggs. Very little is known about the effects of man‐made alterations to the river flow regime on the reproductive activity of fishes in the majority of South African river systems. The agriculturally based flooding regime at Beervlei may have increased the recruitment of the redfin minnow species. Water management must give cognizance to the biological and environmental requirements within the regulated river systems. Water release strategies from Beervlei Dam should include instream flow decisions based on the requirements of the aquatic environment as well as for agricult

ISSN:0886-9375    

DOI:10.1002/rrr.3450060105

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMangrove Creek Dam, the eighth highest dam in NSW, Australia has induced a complex response of the downstream, sand‐bed channel. Since dam closure on 1 October 1981, mean daily flows and the peak instantaneous discharge of floods have been reduced greatly (up to 94 per cent) and nearly 100 per cent of the incoming sediment load has been trapped behind the Dam. The magnitude of the hydrologic effects decreases with distance downstream. River response varies in direct proportion to the magnitude of the altered hydrologic regime and includes alternating but localized bed aggradation and degradation as well as channel contraction. Contraction has occurred by a combination of in‐channel bench construction, the formation and bank attachment of longitudinal bars and bank deposition.Leptospermum polygalifoliumhas rapidly colonized these in‐channel deposits and will result in the stabilization of benches. Armouring has not been a significant feedback process to date because of the limited degradation and low gravel supply. It is postulated that the above trends will continue, thus converting the former large, straight, active sand‐bed channel into a small, sinuous, well‐ vegetated sand

ISSN:0886-9375    

DOI:10.1002/rrr.3450060106

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450060107

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450060101

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY