摘要:

A simplified watershed model has been developed to examine and analyze the high rainfall response of a small, steep, and forested watershed in coastal British Columbia. Hourly data for both rainfall and streamflow are used. Rainfall is measured at five points evenly distributed throughout the watershed. The model is found to perform well and indicates that the hydrologic response of the watershed is reasonably linear, except for intense summer rainstorms under dry soil conditions. The linearity and the rapidity of the watershed response is attributed to the response of the subsurface pipeflow. An analysis of a particular case of soil pipe development shows that the pipeflow system can respond linearly and rapidly to the rainfall input.Key words: watershed modelling, hydrologic response, soil piping.

ISSN:0315-1468    

DOI:10.1139/l93-001

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Four snow dump sites in the Ottawa-Carleton region were analyzed for BOD, total and fecal coliforms, chlorides, sulfates, specific conductance, suspended solids, metals, and other parameters. Sites were sampled at various depths during the months of February through May. There was no trend in variation of quality in the dump piles with time. The black crust that formed on the top of the pile was heavily laden with solids and metals.Snowmelt samples were also taken over the same time period and analyzed for the above parameters. The process of snowmelt reduced the concentrations of most metals and suspended solids from the dump by 50–70%. Dissolved constituents in snowmelt are discharged at very high levels during the initial stages of snowmelt and rapidly decrease to low concentrations. Suspended solids and associated metals in snowmelt exhibited variability with snowmelt conditions and the state of the dump pile. The concentrations of a number of metals in settled snowmelt exceeded provincial objectives for surface waters.An analysis of settled snow dump and snowmelt samples for suspended solids and metals was conducted for settling periods of 1, 6, 12, and 24 h. A settling time from 2 to 6 h would achieve most of the removal that could be expected from sedimentation. The overall removal of suspended solids and the metals in settled snowmelt would generally be better than 90%. There were no significant trends in removal behavior as the snowmelt season progressed. The removal of metals lagged slightly behind the removal of suspended solids after settling because of the stronger association of metals with smaller sediment particles. The residue at the dump site is highly contaminated.Key words: snowmelt, runoff, stormwater, sedimentation, road deicing, snow dump, pollution.

ISSN:0315-1468    

DOI:10.1139/l93-002

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Pilot-scale research into the characterization and enhancement of the aerobic digestion of waste-activated sludges was performed. Waste sludge from two sources was aerobically digested at varying operating temperatures; to offset the naturally occurring mixed liquor pH (MLpH) decrease due to nitrification, small amounts of Ca(OH)2or NaHCO3were added to maintain target MLpH levels of pH 6, 7, and 8. Results indicated that volatile mass reduction was severely curtailed at low MLpH, but could be significantly improved through MLpH control, with increases of > 100% in performance over the low MLpH reactor noted. However, the process was found to be very "sludge-specific", in that the two test sludges behaved quite differently under similar operating conditions. A separate mass balance on the nonvolatile sludge fraction illustrated the action of the controlling chemicals in terms of reduction in cell lysis; it was also observed that some precipitation of inorganic materials was occurring, depending on chemical type and dose. While it was not possible to suggest an optimized chemical and dose, it was concluded that this process had very real potential for full-scale implementation, as an effective and simple method for rehabilitation of poorly functioning digesters.Key words: aerobic sludge digestion, Ca(OH)2, enhancement, inhibition, mixed liquor pH control, NaHCO3, volatile and nonvolatile suspended solids.

ISSN:0315-1468    

DOI:10.1139/l93-003

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

During the last two decades, emphasis in transportation planning has shifted from long-term capital-intensive construction projects to short- and medium-term, relatively low capital cost, projects aimed at using existing transportation facilities more efficiently. This shift caused the integration of transportation system management (TSM) activities into the overall transportation planning process. Presently, the TSM endeavours are regarded as a prerequisite prior to initiating major capacity expansion type of capital works.Although the TSM initiatives are undertaken in response to congestion (delay), energy, environment, and safety concerns, reducing delay is a key measure of effectiveness. Despite the importance of this factor, there is a lack of efficient tools that are capable of estimating delay corresponding to TSM endeavours. Most, if not all, of the existing delay models have been developed for detailed operational analysis. These models are data-intensive and require highly specialized human and machine types of resources.In this research, multi-link streets and networks were synthesized and their performance in delay terms was estimated through the use of a microscopic simulation program,NETSIM. The output ofNETSIM, in conjunction with physical and traffic characteristics of networks, were used to develop the multiple regression type of macro-simulation models of delay. The regression models developed are capable of estimating vehicle delay for urban streets. Field data collected by using the videotape technology and maps were utilized to validate the models.Key words: delay, model, simulation, traffic, transportation, urban.

ISSN:0315-1468    

DOI:10.1139/l93-004

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A theoretical and experimental study on unidirectional spreading of oil under solid ice in calm waters is presented. The emphasis of the study is on the dominant spreading mechanism for oil under ice, which is the buoyancy-viscous phase. The equations derived cover both the constant discharge and the constant volume modes. Laboratory experiments were conducted for ice cover roughnesses varying from smooth to rough, using different discharge rates, and oils of different viscosities. The experimental results agree closely with the theory.Key words: oil spreading, oil slicks, oil under ice, buoyancy-viscous phase, constant discharge, constant volume.

ISSN:0315-1468    

DOI:10.1139/l93-005

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A biological process of heavy metals solubilization and sewage sludge stabilization was studied in a batch reactor of 30-L capacity. The acclimatized leaching microflora was composed of two major groups of thiobacilli: less acidophilic and acidophilic. A batch time of 10 days allows a substantial metal solubilization: cadmium (100%), copper (80%), manganese (80%), nickel (46%), and zinc (100%). The bioleaching process also causes a significative decrease in sludge total suspended solids (25%) and volatile suspended solids (32%), and a considerable reduction (under the detection limit of 10 cfu∙mL−1) of indicator bacteria (total coliforms, fecal coliforms, fecal streptococci). After filtration or centrifugation of the leached sludge, the solubilized metals were precipitated by lime neutralization. The phosphorus and potassium sludge contents were not affected by bioleaching process. These results indicate that the process of sludge digestion and metal leaching can be conducted in parallel in the same reactor.Key words: sewage sludge, heavy metals, bioleaching, stabilization, thiobacilli, elemental sulfu

ISSN:0315-1468    

DOI:10.1139/l93-006

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

This paper presents a new method for critical path (CPM) scheduling that optimizes project duration in order to minimize the project total cost. In addition, the method could be used to produce constrained schedules that accommodate contractual completion dates of projects and their milestones. The proposed method is based on the well-known "direct stiffness method" for structural analysis. The method establishes a complete analogy between the structural analysis problem with imposed support settlement and that of project scheduling with imposed target completion date. The project CPM network is replaced by an equivalent structure. The equivalence conditions are established such that when the equivalent structure is compressed by an imposed displacement equal to the schedule compression, the sum of all member forces represents the additional cost required to achieve such compression. To enable a comparison with the currently used methods, an example application from the literature is analyzed using the proposed method. The results are in close agreement with those obtained using current techniques. In addition, the proposed method has some interesting features: (i) it is flexible, providing a trade-off between required accuracy and computational effort, (ii) it is capable of providing solutions to CPM networks where dynamic programming may not be directly applicable, and (iii) it could be extended to treat other problems including the impact of delays and disruptions on schedule and budget of construction projects.Key words: construction scheduling, time–cost trade-off, project cost optimization, scheduling with constraints, project acceleration.

ISSN:0315-1468    

DOI:10.1139/l93-007

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A simple structural model is proposed to evaluate the axial force acting on tie beams interconnecting spread footings or pile caps due to differential ground motion estimated on the basis of the travelling wave assumption. The approach is intended to supplement the "ten percent rule" or similar multipliers specified by seismic codes as design axial forces on tie beams. It is shown that the axial force demand is rather modest. However, shear forces between footing and soil may be quite large depending on maximum column displacements and superstructure rigidity.Key words: foundations, tie beams, earthquake, travelling waves, seismic codes.

ISSN:0315-1468    

DOI:10.1139/l93-008

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The problem of estimating suspended sediment yields from ungauged watersheds is described. Results from regression analyses using hydroclimatic and geomorphic variables are presented for 14 watersheds in Atlantic Canada. Estimates are given for long-term mean suspended sediment yields and for annual suspended sediment yields for a particular year. The effects of incorporating an added constant term in the regression equation are considered. Limited tests are presented for two small watersheds not used in the development of the adopted regression equations.Key words: suspended sediment yields, ungauged watersheds, regression analysis, Atlantic Canada.

ISSN:0315-1468    

DOI:10.1139/l93-009

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A numerical model calledRIVJAMhas been developed to compute the configuration of and water levels caused by ice jams of the "wide" kind, under natural stream conditions and regardless of whether the jam has attained its full potential, known as equilibrium. Account of seepage flow through the voids of the jam enables predictions of grounding conditions to be made, in accord with observations. The model is applied to three case studies of ice jam events and found to perform satisfactorily. The various model coefficients fall within the expected ranges, with the exception of a parameter characterizing the intensity of seepage flow. More field data are needed to elucidate this matter.Key words: grounding, ice, jam, model, numerical, river, seepage, thickness, toe, wide.

ISSN:0315-1468    

DOI:10.1139/l93-010

出版商:NRC Research Press    

年代:1993

数据来源: NRC