FLUVIAL PROCESSES AND MORPHOLOGICAL THRESHOLDS IN INCISED CHANNEL RESTORATION1

ABSTRACT: Incised channels are those in which an imbalance between sediment transport capacity and sediment supply has led to degradation of their beds. This is a frequent response to stream channelization, changes in land use, or lowering of base level. If the degradation causes a critical bank-height threshold to be exceeded, which is dependent on the geotechnical properties of the bank materials, then bank failure and channel widening follow. Interdependent adjustments of channel slope and cross-sectional area occur until a new state of dynamic equilibrium with the imposed discharge and sediment load is attained. These geomorphic adjustments can be described and quantified by using location-for-time substitution and a model of channel evolution can be formulated. Three approaches to rehabilitation of the degraded channels are possible; geomorphic, engineering and rational. The rational approach, which integrates elements of both the engineering and geomorphic approaches, is based on the channel evolution model, and it generally involves control of grade, control of discharge, or a combination of both.     

Diurnal models of traffic-generated CO for Penang,Malaysia

Georgetown of Penang, an old city, is noted for its narrow streets. The existing traffic dispersal system is utterly inadequate to cope with the ever increasing number of cars and motorcycles on the road. The principal objective of this study is to build prediction models of CO to be employed as one of the planning tools in the future design of Penang urban traffic dispersal system. This study involves the monitoring of kerbside CO levels at selected sites and the fitting of hourly-averaged CO data to linear regression models incorporating the residual effect of CO emission due to traffic in the earlier periods and also different categories of vehicles. The best overall regression model appears to be the one based upon the total traffic count of motorcycles. This can be accounted for by the fact that the traffic counts of motorcycles and cars are highly correlated in most cases and that the emissions of CO from motorcycles are more readily detected as they travel closer to the kerb. The inclusion of residual CO in the models significantly improves the correlation coefficient from about 0.4 to about 0.7.     

QUANTIFICATION OF INCISED CHANNEL EVOLUTION AND EQUILIBRIUM1

ABSTRACT: Incised channels are caused by an imbalance between sediment transport capacity and sediment supply that alters channel morphology through bed and bank erosion. Consistent sequential changes in incised channel morphology may be quantified and used to develop relationships describing quasi‐equilibrium conditions in these channels. We analyzed the hydraulic characteristics of streams in the Yazoo River Basin, Mississippi in various stages of incised channel evolution. The hydraulic characteristics of incising channels were observed to follow the sequence predicted by previous conceptual models of incised channel response. Multiple regression models of stable slopes in quasi‐equilibrium channels that have completed a full evolutionary sequence were developed. These models compare favorably with analytical solutions based on the extremal hypothesis of minimum stream power and empirical relationships from other regions. Appropriate application of these empirical relationships may be useful in preliminary design of stream rehabilitation strategies.     

Assessing anthropogenic impact on Mediterranean sand dunes from aerial digital photography

The Mediterranean region plays host to ca. 33% of the world’s tourism industry. This population of visitors (ca. 147 million in 1990) inevitably exerts an enormous impact on the natural resources of this coastal zone. In May 1997, a new generation Aerial Digital Photographic System [ADPS] configured with a Kodak Digital Science 460 CIR digital camera was used to acquire colour infrared digital photographs of the sand dune systems along the Mediterranean coast of France, from Le Barcares to St-Cyprien-Plage. These have been used to assess the condition of the dunes along this coast. A series of simple analytical techniques to identify and measure features indicative of public pressure using image processing software has been devised. The dune manager with basic computer skills can analyse such indicators as path length, vegetation cover (and conversely the extent of bare sand) to enable monitoring of the performance of their dune systems under particular management regimes. These photographs have been compared with similar digital photographs of dune sites in SW France to allow a comparison of dune degradation in a region with a different population pressure and climate regime. Dune systems sampled from the Mediterranean coastal zone showed more evidence of anthropogenically induced change than those sampled in SW France.     

Influence of HCl on oxidation of gaseous elemental mercury by dielectric barrier discharge process

The influence of HCl on the oxidation of gaseous elemental mercury (Hg0) has been investigated using a dielectric barrier discharge (DBD) plasma process, where the temperature of the plasma reactor and the composition of gas mixtures of HCl, H2O, NO, and O2 in N2 balance have been varied. We observe that Cl atoms and Cl2 molecules, created by the DBD process, play important roles in the oxidation of Hg0 to HgCl2. The addition of H2O to the gas mixture of HCl in N2 accelerates the oxidation of Hg0, although no appreciable effect of H2O alone on the oxidation of Hg0 has been observed. The increase of the reaction temperature in the presence of HCl results in the reduction of Hg0 oxidation efficiency probably due to the deterioration of the heterogeneous chemical reaction of Hg0 with chlorinated species on the reactor wall. The presence of NO shows an inhibitory effect on the oxidation of Hg0 under DBD of 16% O2 in N2, indicating that NO acts as an O and O3 scavenger. At the composition of Hg0 (280 microg m(-3)), HCl (25 ppm), NO (204 ppm), O2 (16%) and N2 (balance) and temperature 90 degrees C, we obtain the nearly complete oxidation of Hg0 at a specific energy density of 8 J l(-1). These results lead us to suggest that the DBD process can be viable for the treatment of mercury released from coal-fired power plants.     

A sensitive and robust method for the determination of alkylphenol polyethoxylates and their carboxylic acids and their transformation in a trickling filter wastewater treatment plant

This paper presents a method for the determination of alkylphenols, alkylphenol polyethoxylates (APEO) and alkylphenol ethoxycarboxylates (APEC) in the aqueous and particulate phase of wastewater samples. Quantification was achieved by liquid chromatography-tandem mass spectrometry. The sensitivity of the method is demonstrated by low detection limits, in the dissolved phase 1.2-9.6ngl(-1) for alkylphenol, AP(1-3)EO and APEC and 0.1-4.1ngl(-1) for longer chain alkylphenol polyethoxylates. The method detection limit for particulate phase samples ranged from 6 to 60ngg(-1) for AP, AP(1-3)EO and APEC; with the longer chain APEO being from 0.5 to 20ngg(-1). Matrix effects were noted in complex matrix rich samples. There was a distinct change in the distribution of alkylphenol ethoxylates during biological treatment of the wastewater, with the major biotransformation products observed being carboxylated derivatives at concentrations of up to 1768ngl(-1). Shorter chain APEO were present in higher proportions in the suspended solids, due to their higher affinity to particulate matter compared to the long-chain oligomers.     

PART I: METHODOLOGY AND PROBLEMS IN AN URBANIZED ARID ENVIRONMENT1

The methodology of operations research is judged in relation to its utility to water resource management in an urbanized arid environment and to the study of worth of data for such management. Conditions for existence of a managerial problem are reviewed as is the multilevel structure of the decision process, including decisions on social goals for Western water use. Worth of data can only be judged in relation to a particular use to meet a social or managerial objective. The role of data uncertainty on the decision process is reviewed in the light of past water decisions and present and future problems.     

EFFECTS OF URBANIZATION ON CHANNEL INSTABILITY1

ABSTRACT: Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process‐based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk‐based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed‐specific conditions. In addition to the storage characteristics of the pre‐development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk‐based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.     

A simulation model for projecting changes in salinity concentrations and species dominance in the coastal margin habitats of the Everglades

Sharp boundaries typically separate the salinity tolerant mangroves from the salinity intolerant hardwood hammock species, which occupy the similar geographical areas of southern Florida. Evidence of strong feedback between tree community-type and the salinity of the unsaturated (vadose) zone of the soil suggests that a severe disturbance that significantly tilts the salinity in the vadose zone might cause a shift from one vegetation type to the other. In this study, a model based upon the feedback dynamics between vegetation and salinity of the vadose zone of the soil was used to take account of storm surge events to investigate the mechanisms that by which this large-scale disturbance could affect the spatial pattern of hardwood hammocks and mangroves. Model simulation results indicated that a heavy storm surge that completely saturated the vadose zone at 30 ppt for 1 day could lead to a regime shift in which there is domination by mangroves of areas previously dominated by hardwood hammocks. Lighter storm surges that saturated the vadose zone at less than 7 ppt did not cause vegetation shifts. Investigations of model sensitivity analysis indicated that the thickness of the vadose zone, coupled with precipitation, influenced the residence time of high salinity in the vadose zone and therefore determined the rate of mangrove domination. The model was developed for a southern Florida coastal ecosystem, but its applicability may be much broader.     

Herbivory mediates grass-endophyte relationships

Endophytic fungi are plant symbionts living asymptomatically within plant tissues. Neotyphodium spp., which are asexual vertically transmitted systemic fungal endophytes of cool-season grasses, are predicted to be plant mutualists. These endophytes increase host plant resistance to environmental stresses and/or increase the production of alkaloid-based herbivore deterrents. The ubiquity of this defense mutualism is unclear, and a variety of alternative mechanisms may explain the observed variation in infection rates, levels of deterrence, and the maintenance of asexual endophytes in grass populations. We found that grass-endophyte interactions are variable and ordered along an herbivory gradient in an undisturbed subarctic alpine ecosystem. Native grass populations in grazed sites had significantly greater frequency of Neotyphodium infection compared to ungrazed sites. Tillers from grazed sites had significantly higher hyphal densities compared to ungrazed sites. The ability of grass-Neotyphodium constituents to deter vertebrate herbivory in natural systems is thought to be rare. In grazed meadows, we showed that endophyte infection resulted in the deterrence of grazing by native vertebrate herbivores. However, the same herbivores did not distinguish between infected and uninfected grass harvested from ungrazed areas. These results demonstrate that the relationship between vertically transmitted endophytes and grasses in the alpine tundra vary greatly within populations. This may be based in part on defense mutualism and is consistent, under varying levels of herbivory, with the predictions of optimal defense theory.