Adjacent Drainage Basins Research Articles

Ecological models for estimating breakpoints and prediction intervals.

The relationships between an environmental variable and an ecological response are usually estimated by models fitted through the conditional mean of the response given environmental stress. For example, nonparametric loess and parametric piecewise linear regression model (PLRM) are often used to represent simple to complex nonlinear relationships. In contrast, piecewise linear quantile regression models (PQRM) fitted across various quantiles of the response can reveal nonlinearities in its range of variation across the explanatory variable.We assess the number and positions of candidate breakpoints using loess and compare the relative efficiencies of PLRM and PQRM to quantitatively determine the breakpoints' location and precision. We propose a nonparametric method to generate bootstrap confidence intervals for breakpoints using PQRM and prediction bands for loess and PQRM. We illustrated the applications using data from two aquatic studies suspected to exhibit multiple environmental breakpoints: relating a fish multimetric index of community health (MMI) to agricultural activity in wetlands' adjacent drainage basins; and relating cyanobacterial biomass to total phosphorus concentration in Canadian lakes.Two statistically significant breakpoints were detected in each dataset, demarcating boundaries of three linear segments, each with markedly different slopes. PQRM generated less biased, more accurate, and narrower confidence intervals for the breakpoints and narrower prediction bands than PLRM, especially for small samples and large error variability. In both applications, the relationship between the response and environmental variables was weak/nonsignificant below the lower threshold, strong through the midrange of the environmental gradient, and weak/nonsignificant beyond the upper threshold.We describe several advantages of PQRM over PLRM in characterizing environmental relationships where the scatter of points represents natural environmental variation rather than measurement error. The proposed methodology will be useful for detecting multiple breakpoints in ecological applications where the limits of variation are as important as the conditional mean of a function.

A Study on the Improvement of Reliability Estimation Method for Sewer Network considering Resilience

In city centers, the damage caused by inundation is aggravated by rising populations and urbanization, which extend impermeable areas. Research is needed to identify the inundation risks caused by climate change and quantitatively assess the consequences. In this study, we proposed an improved reliability study which considers resilience in the original evaluation method for the reliability of a storm sewer network. Rainfall-runoff analysises were performed on a part of Bangbae 2 drainage basin in Seoul by applying Storm Water Management Model 5 Ver. Based on the results of the application of excessive rainfall events, the original reliability evaluation method was compared with the improved reliability evaluation method. Consequently, the effect of the improvement of the cluster about 30% was confirmed when selection the central value rather than the existing representative value. The improved reliability evaluation method proposed in this study can be used as a design objective function and as an index for evaluating the inundation risk in adjacent drainage basins.

Statistical assessment of background levels for metal contamination from a subtropical estuarine system in the SW Atlantic (Paranaguá Estuarine System, Brazil)

Trace metal background levels determination is essential for the proper assessment of the contamination status of a region. This study aims to integrate geochemical and statistical methods for the reliable determination of background levels, applying it to the sediments of the Paranagua Estuarine System (PES), a large subtropical estuarine system of international importance since it is considered a World Heritage Site and Biosphere Reserve and it harbors the main South American grain shipping port. Prediction Interval (PI) was applied as a chemometric tool to evaluate metal enrichment without a reference level and assess a regional background. Moreover, the sources and concentrations of major and trace elements were assessed in surface sediments from 135 sampling sites located in the Paranagua Estuarine System (PES). PES surface sediment elements concentrations may be considered lower than those found in other anthropized environments indicating no significant contamination for most of the studied elements (Cr, Cu, Ni, Pb and Zn). The levels of As in the PES may be related to the geochemical characteristics of the adjacent drainage basin and the occurrence of phosphate rocks, which contain As in their composition. However, As was also influenced by anthropogenic inputs either from agricultural activities or fertilizer industries working with mining phosphate in the region.

Simulation of water flow management by the flood control facilities in the adjacent river basins

A systematic approach to reducing the risk of flooding is considered. The main idea of it is to switch from the flood control only by the one hydro system on the main river but to control the whole river system, including many adjacent river basins at various levels. This proposal expands the possibility of using a flood control system of self-regulating hydro systems distributed on adjacent drainage basins at multiple levels by organizing their joint work, ensuring that the maximum allowable water flow in the control sections of the river system is not exceeded. Using the proposed approach will allow protecting from flooding significant areas of land in the lower pool of the main hydroelectric complex in the context of climate change.

A versatile, linear complexity algorithm for flow routing in topographies with depressions

Abstract. We present a new algorithm for solving the common problem of flow trapped in closed depressions within digital elevation models, as encountered in many applications relying on flow routing. Unlike other approaches (e.g., the Priority-Flood depression filling algorithm), this solution is based on the explicit computation of the flow paths both within and across the depressions through the construction of a graph connecting together all adjacent drainage basins. Although this represents many operations, a linear time complexity can be reached for the whole computation, making it very efficient. Compared to the most optimized solutions proposed so far, we show that this algorithm of flow path enforcement yields the best performance when used in landscape evolution models. In addition to its efficiency, our proposed method also has the advantage of letting the user choose among different strategies of flow path enforcement within the depressions (i.e., filling vs. carving). Furthermore, the computed graph of basins is a generic structure that has the potential to be reused for solving other problems as well, such as the simulation of erosion. This sequential algorithm may be helpful for those who need to, e.g., process digital elevation models of moderate size on single computers or run batches of simulations as part of an inference study.

Landscape response to progressive tectonic and climatic forcing in NW Borneo: Implications for geological and geomorphic controls on flood hazard

Empirical models have simulated the consequences of uplift and orographic-precipitation on the evolution of orogens whereas the effects of these forcings on ridgelines and consequent topography of natural landscapes remain equivocal. Here we demonstrate the feedback of a terrestrial landscape in NW Borneo subject to uplift and precipitation gradient owing to orographic effect, and leading to less-predictable flooding and irreversible damages to life and property. Disequilibrium in a large catchment recording the lowest rainfall rates in Borneo, and adjacent drainage basins as determined through χ, a proxy for steady–state channel elevation, is shown to result in dynamic migration of water divide from the windward-side of the orogen towards the leeward-side to attain equilibrium. Loss of drainage area in the leeward-side reduces erosion rates with progressive shortening resulting in an unstable landscape with tectonic uplift, gravity faults and debris flows. 14C dating of exhumed cut-and-fill terraces reveal a Mid–Pleistocene age, suggesting tectonic events in the trend of exhumation rates (>7 mm a−1) estimated by thermochronology, and confirmed by morphotectonic and sedimentological analyses. Our study suggests that divide migration leads to lowered erosion rates, channel narrowing, and sediment accretion in intermontane basins on the leeward-side ultimately resulting in enhanced flooding.

DRAINAGE NETWORK ALTERATIONS: CAUSES AND FACTORS

Three main causes of river network alterations are described. 1. External impacts or complex of several impacts on drainage basin . These impacts may be caused by tectonic movements, volcanism, climatic changes, oscillations of end basin level and abrasive activity related to transgression. Their results may be whether broad and cover a series of neighbour basins, or local one. 2. Interaction of adjacent drainage basins with different velocity of inner processes . 3. The change of relief type within drainage basin (for instance from mountain into plain one) followed by alteration of types and velocities of major relief formation processes .

Erosion rates in and around Shenandoah National Park, Virginia, determined using analysis of cosmogenic 10Be

We use cosmogenic 10Be analysis of fluvial sediments and bedrock to estimate erosion rates (104-105 year timescale) and to infer the distribution of post-orogenic geomorphic processes in the Blue Ridge Province in and around Shenandoah National Park, Virginia. Our sampling plan was designed to investigate relationships between erosion rate and lithology, mean basin slope, basin area, and sediment grain size. Fifty-nine samples were collected from a variety of basin sizes ( Inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3.0 to 21 m/My. The area-weighted mean erosion rate for single-lithology basins in the Park is 12.2 m/My. Single-lithology erosion rate ranges for fluvial samples are: granite, 7.0 to 20 m/My; metabasalt, 3.8 to 21 m/My; quartzite, 3.8 to 15 m/My; and siliciclastic rocks, 5.2 to 15 m/My. Multilithology basins erode at rates between 3.0-16 m/My. The Shenandoah River basin (3305 km2) is eroding at 6.6 m/My. Bedrock erosion rates range from 1.8 to 11 m/My across all lithologies, with a mean of 6.5 ± 4.3 m/My. Grain-size specific 10Be analysis of four samples showed no consistent trend of concentration with grain size. Cosmogenic analysis of bedrock and sediment from the Shenandoah National Park area allows us to speculate about why some parts of the Appalachian Mountains erode more slowly and some more rapidly. Overall, it appears that steep drainage basins erode more rapidly than gently sloped basins. Climate and lithology may also influence basin-scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite- and granite-dominated basins. Data are conflicting in regards to the evolution of relief over time. Analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins (Susquehanna River, Shenandoah National Park region) or at similar rates (Great Smoky Mountains) providing a mechanism for growing relief at the scale of individual ridgelines. However, considering relief on a landscape or physiographic province scale, by comparing erosion rates of the highlands versus the lowlands, suggests that relief of the range as a whole is either steady or very slowly decreasing over multi-millennial timescales. The presence of significant erosion rate/slope relationships negates a broad Hackian view of the landscape because there is not uniform erosion across this landscape. The aspect-erosion rate and slope-erosion rate relationships present in the Shenandoah area suggest that the landscape is not fully adjusted to rock strength.

Development and characterization of seven polymorphic microsatellite loci in Bembidion atrocaeruleum (Coleoptera: Carabidae).

We isolated seven polymorphic microsatellite loci from a ground beetle ( Bembidion atrocaeruleum , Coleoptera, Carabidae (Stephens, 1826)) associated with naturally and regularly disturbed floodplain habitat in northwest Europe. Loci were tested on 157 individuals collected from five distinct habitat patches across two adjacent drainage basins in Wales, United Kingdom, to assess their potential for revealing population structure across a relatively short spatial extent. Alleles per locus ranged from 4 to 12. For a central representative population, expected heterozygosity ranged from 0.23 to 0.78 (mean: 0.63), and observed heterozygosity ranged from 0.16 to 0.94 (mean: 0.56). Analysis of molecular variance indicated significant structure among populations, even when one locus potentially containing null alleles was removed. These loci have the potential to aid the study of dispersal mechanisms of this important riparian species along and between river corridors, a recurring question in floodplain conservation studies. In addition, given the diversity of the Bembidion genus, they may have utility in the study of sister species.

Effect of Water Management on Interannual Variation in Bulk Soil Properties from the Eastern Coastal Everglades

We examined interannual variation in soil properties from wetlands occurring in adjacent drainage basins from the southeastern Everglades. Triplicate 10-cm soil cores were collected, homogenized, and analyzed during the wet season 2006–2010 from five freshwater sawgrass wetland marshes and three estuarine mangrove forests. Soil bulk density from the Taylor Slough basin ranged from 0.15 gm-cm−3 to 0.5 gm-cm−3, was higher than from the Panhandle basin every year, and generally increased throughout the study period. Organic matter as a percent loss on ignition ranged from 7 % to 12 % from freshwater marshes and from 13 % to 56 % from estuarine mangroves. Extractable iron in soils was similar among drainage basins and wetland types, typically ranging from 0.6 to 2.0 g Fe kg−1. In contrast, inorganic sulfur was on average over four times higher from estuarine soils relative to freshwater, and was positively correlated with soil organic matter. Finally total soil phosphorus (P) was lower in freshwater soils relative to estuarine soils (84 ± 5 versus 326 ± 32 mg P kg−1). Total P from the freshwater marshes in the Panhandle basin rose throughout the study period from 54.7 ± 8.4 to 107 ± 17 mg P kg−1, a possible outcome of differences in water management between drainage basins.

Abandonment ages of alluvial landforms in the hyperarid Negev determined by luminescence dating

Dating the time of abandonment of geomorphic surfaces in the arid mid latitudes is necessary for studies ranging from tectonics, landscape evolution and paleoclimate. It has often been hampered by the limited material suitable for conventional isotopic methods and the uncertainties inherent in cosmogenic radionuclide methods. We propose luminescence dating as a suitable method for dating the time of abandonment of aggradational geomorphic surfaces in the hyperarid regions. We dated the top of such surfaces with different age ranges and geomorphic settings in a sequence of alluvial fans in Nahal Shehoret in the southern Negev and in a sequence of terraces in Nahal Ze'elim and in Nahal Zin, two adjacent drainage basins in the Judean Desert, Israel. Samples were collected from beneath the gypsic horizon at a depth of 0.3–0.7 m, below which sand grains do not penetrate. Depositional ages for the uppermost beds of the landforms, which are proxies for abandonment, range from ∼90 ka to ∼5 ka. In all three basins, the ages are in morphostratigraphic order and agree well with relative age estimates based on soil chronosequences and on Lake Lisan levels. Abandonment ages for an individual alluvial fan cluster within ±10–20%, therefore it is possible to distinguish between surfaces with ages differing by more than 20%. Thus, in hyperarid areas, the luminescence methods can be used for surface dating.

Amazonian magnetostratigraphy: Dating the first pulse of the Great American Faunal Interchange

Abstract The chronostratigraphy of the youngest Neogene deposits of the Amazon Basin, which comprise the Madre de Dios Formation in eastern Peru, remains unresolved. Although 40 Ar/ 39 Ar dates on two volcanic ashes from this formation in Peru provide critical baseline data points, stratigraphic correlations among scattered riverine outcrops in adjacent drainage basins remain problematic. To refine the chronostratigraphy of the Madre de Dios Formation, we report here the magnetostratigraphy of an outcrop on the Madre de Dios River in southeastern Peru. A total of 18 polarity zones was obtained in the ∼65-m-thick Cerro Colorado section, which we correlate to magnetozones Chrons C4Ar to C2An (9.5–3.0 Ma) based on the prior 40 Ar/ 39 Ar dates. These results confirm the late Miocene age of a gomphothere recovered from the Ipururo Formation, which underlies the late Miocene Ucayali Unconformity at the base of the Cerro Colorado outcrop. The results also support earlier interpretations of a late Miocene age for other fossils of North American mammals recovered from basal conglomeratic deposits of the Madre de Dios Formation immediately above the Ucayali Unconformity. These mammals include other gomphotheres, peccaries, and tapirs, and their presence in South America in the late Miocene is recognized as part of the first pulse of the Great American Faunal Interchange.

Controls on the spacing of first‐order valleys

Many landscapes are composed of ridges and valleys that are uniformly spaced, even where valley locations are not controlled by bedrock structure. Models of long‐term landscape evolution have reproduced this phenomenon, yet the process by which uniformly spaced valleys develop is not well understood, and there is no quantitative framework for predicting valley spacing. Here we use a numerical landscape evolution model to investigate the development of uniform valley spacing. We find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area (a proxy for water flux) and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium. Valley spacing is most sensitive to the relative rates of advective erosion processes (such as stream incision) and diffusion‐like mass transport (such as soil creep) and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision. Analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a Péclet number. We use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape. The observed scaling relationships also provide insight into the cause of transitions from rill‐like drainage networks to branching networks, the spatial scale of first‐order drainage basins, the contributing area at which hillslopes transition into valleys, and the narrow range of width‐to‐length ratios of first‐order basins.

Contrasting rainfall generated debris flows from adjacent watersheds at Forest Falls, southern California, USA

Debris flows are widespread and common in many steeply sloping areas of southern California. The San Bernardino Mountains community of Forest Falls is probably subject to the most frequently documented debris flows in southern California. Debris flows at Forest Falls are generated during short-duration high-intensity rains that mobilize surface material. Except for debris flows on two consecutive days in November 1965, all the documented historic debris flows have occurred during high-intensity summer rainfall, locally referred to as ‘monsoon’ or ‘cloudburst’ rains. Velocities of the moving debris range from about 5 km/h to about 90 km/h. Velocity of a moving flow appears to be essentially a function of the water content of the flow. Low velocity debris flows are characterized by steep snouts that, when stopped, have only small amounts of water draining from the flow. In marked contrast are high-velocity debris flows whose deposits more resemble fluvial deposits. In the Forest Falls area two adjacent drainage basins, Snow Creek and Rattlesnake Creek, have considerably different histories of debris flows. Snow Creek basin, with an area about three times as large as Rattlesnake Creek basin, has a well developed debris flow channel with broad levees. Most of the debris flows in Snow Creek have greater water content and attain higher velocities than those of Rattlesnake Creek. Most debris flows are in relative equilibrium with the geometry of the channel morphology. Exceptionally high-velocity flows, however, overshoot the channel walls at particularly tight channel curves. After overshooting the channel, the flows degrade the adjacent levee surface and remove trees and structures in the immediate path, before spreading out with decreasing velocity. As the velocity decreases the clasts in the debris flows pulverize the up-slope side of the trees and often imbed clasts in them. Debris flows in Rattlesnake Creek are relatively slow moving and commonly stop in the channel. After the channel is blocked, subsequent debris flows cut a new channel upstream from the blockage that results in the deposition of new debris-flow deposits on the lower part of the fan. Shifting the location of debris flows on the Rattlesnake Creek fan tends to prevent trees from becoming mature. Dense growths of conifer seedlings sprout in the spring on the late summer debris flow deposits. This repeated process results in stands of even-aged trees whose age records the age of the debris flows.

Toward Reversal of Eutrophic Conditions in a Subtropical Estuary: Water Quality and Seagrass Response to Nitrogen Loading Reductions in Tampa Bay, Florida, USA

Coastal waters have been significantly influenced by increased inputs of nutrients that have accompanied population growth in adjacent drainage basins. In Tampa Bay, Florida, USA, the population has quadrupled since 1950. By the late 1970s, eutrophic conditions including phytoplankton and macroalgal blooms and seagrass losses were evident. The focus of improving Tampa Bay is centered on obtaining sufficient water quality necessary for restoring seagrass habitat, estimated to have been 16,400 ha in 1950 but reduced to 8800 ha by 1982. To address these problems, targets for nutrient load reductions along with seagrass restoration goals were developed and actions were implemented to reach adopted targets. Empirical regression models were developed to determine relationships between chlorophyll a concentrations and light attenuation adequate for sustainable seagrass growth. Additional empirical relationships between nitrogen loading and chlorophyll a concentrations were developed to determine how Tampa Bay responds to changes in loads. Data show that when nitrogen load reduction and chlorophyll a targets are met, seagrass cover increases. After nitrogen load reductions and maintenance of chlorophyll a at target levels, seagrass acreage has increased 25% since 1982, although more than 5000 ha of seagrass still require recovery. The cooperation of scientists, managers, and decision makers participating in the Tampa Bay Estuary Program's Nitrogen Management Strategy allows the Tampa Bay estuary to continue to show progress towards reversing many of the problems that once plagued its waters. These results also highlight the importance of a multi-entity watershed management process in maintaining progress towards science-based natural resource goals.

U–Pb zircon ages as a sediment mixing tracer in the Nepal Himalaya

This paper presents a new approach to quantify sediment mixing based on the mixing of U–Pb zircon age distributions within sediment. Two statistical techniques are presented to determine the proportion in which two known age distributions combine to create a known mixed age distribution. These techniques are then used to determine relative erosion rates between adjacent drainage basins above and below the Main Central Thrust (MCT) in the central Nepal Himalaya. The MCT region is coincident with an abrupt north–south change in geomorphic character and mineral cooling ages that are thought to represent an erosional response to higher rock uplift rates north of the MCT zone. However, it is unclear whether the ongoing deformation responsible for the differential uplift rates is: (1) focused on the MCT; (2) at depth along a crustal scale ramp; or (3) along newly mapped thrust faults south of the MCT. Our study explores this issue by comparing modern erosion rates with longer-term erosion rates determined from mineral cooling ages. Zircons were separated from modern river sand and dated by LA-MC-ICPMS before the measured isotopic ratios and ages were used in 1-d and 2-d mixing calculations. The 1-d technique creates probability density functions of zircon ages for each sample and then uses both an iterative and inverse approach to estimate mixing between samples. In contrast, the 2-d technique estimates mixing between probability “fields” defined by the measured 238U/ 206Pb and 207Pb/ 206Pb ratios. Given a finite mixture with perfect sample representation, both techniques produce perfect mixing estimates across a range of mixing proportions. Modeling results demonstrate that given imperfect subsample representation of the complex parent age distribution, differing degrees of subsample smoothing may be required to achieve an accurate mixing estimate. Using mixing of zircon ages as a quantitative proxy for sediment mixing requires a correction for the concentration of zircon in the river sediment. Two new methods for establishing zircon concentration in river sediment are presented demonstrating the existence of 2- to 5-fold differences in zircon concentration between adjacent drainages. Relative erosion rates are estimated by determining the zircon mixing ratio between adjacent drainages which are then normalized by the ratio of zircon concentrations and the ratio of drainage areas. Results show ∼ 3 times higher modern erosion rates south of the MCT in the northernmost Lesser Himalaya. Future applications of this new technique may include reach-scale sediment transport dynamics, improved sedimentary basin analysis, and better interpretation of foreland mineral cooling ages.

Stable isotopes and electrical conductivity as keys to understanding water pathways and storage in South Cascade Glacier, Washington, USA

AbstractMeasurements of electrical conductivity (EC) and deuterium isotopes in glacier run-off provide the basis for the application of simple mixing models that separate hydrographs into four constitutive components: subglacial, englacial, melt and rainfall-derived waters. Volumes of these components are determined from the models in two adjacent drainage basins within the glacier. Peak arrival times of both EC and isotopes during discharge events on short-term time-scales (days to weeks) differ in each terminus stream by as much as a factor of 5. Englacial water storage determined from the model varied greatly (98%) between neighboring basins within the glacier. Estimates of basal water volumes expressed as a layer thickness at the bed of the glacier differed by 50% (5 and 10mm each). Other results suggest that a greater percentage of water is stored at the glacier bed during rainfall events, and exceeds the storage capacity found within the seasonal snow and englacial zones combined.

Symmetry of Banding Pattern in Banded Killifish (Fundulus diaphanus) from Presque Isle Bay, Lake Erie

ABSTRACT We compared levels of banding symmetry in banded killifish (Fundulus diaphanus Lesueur) from Presque Isle Bay, Lake Erie to two populations outside the bay. One outside population was from the outlet of a stream that flows into Lake Erie (Seven-mile Creek) and the other population was from Lake Pleasant, a lake in an adjacent drainage basin (French Creek). Individuals from Presque Isle Bay had significantly higher levels of fluctuating asymmetry than individuals from the outside sites. One interpretation is that developing embryos are exposed to anthropogenic toxins in Presque Isle Bay resulting in developmental instability.

The hydrology and hydrometeorology of extreme floods in the Great Plains of Eastern Nebraska

The Great Plains of eastern Nebraska occupy a distinctive hydroclimatological niche, characterized by a high frequency of organized thunderstorm systems. A consequence of the hydroclimatology of these systems is a sharp seasonal peak in the regional flood frequency in late June. Pebble Creek and Maple Creek are adjacent drainage basins in the Great Plains of Nebraska with drainage areas of 528 and 1165 km 2 , respectively. The hydrometeorological and hydrologic controls of extreme floods are examined through analyses of a series of five major flood events that occurred in these catchments during the warm season of 1996. Particular attention is given to two storm systems. The 20–21 June flood event was produced by a series of tornadic supercell thunderstorms which tracked over Pebble Creek. The 4–5 August 1996 event, which resulted in record flood peaks in both Pebble Creek and Maple Creek, was produced by a system of multicellular thunderstorms. Analyses of the structure, motion and evolution of these two storm systems provide a conceptual framework for interpreting hydrometeorological controls of scale-dependent flood response. Hydrometeorological analyses are based on both volume scan WSR-88D reflectivity observations from the Omaha, Nebraska radar and composite reflectivity observations from the WSR-88D radar network. Analyses of composite reflectivity observations for the US east of the Rocky Mountains for the 4-year period from 1996 to 1999 are used to place the scale-dependent flood response of the Great Plains within a broader hydroclimatological context. Discharge data for Maple Creek and Pebble Creek, at 15 min time scale, serve as the basis for stream flow analyses. The striking contrasts in flood response between Maple Creek and Pebble Creek are related to contrasts in drainage network structure, infiltration properties and flood wave attenuation. The scale-dependent flood response of these catchments is analyzed in terms of the space-time variability of rainfall as viewed from the spatial perspective imposed by the drainage network of the basin.

Computer modeling of fecal coliform contamination of an urban estuarine system

This study is focused on the investigation of the sources, distribution and fate of fecal coliform populations in the North Fork of the New River that flows through the City of Fort Lauderdale, Florida, USA. The dynamics of this brackish river are driven by weak tides, regulated freshwater discharges, overland runoff, storm water drainage from sewers, and groundwater exchange. Extensive field studies failed to document any alleged source(s) of contamination, including birds, domesticated and undomesticated mammals, humans, septic tank leakage, urban runoff, non-point discharges from agricultural lands, waste disposal from live-aboard vessels and/or in situ re-growth of fecal coliform. In order to facilitate field sampling, and support the data analyses efforts, computer simulations were applied to assess the likelihood of the various possible pollution scenarios. The physically based computer model used is the WASP (Water Quality Analysis Simulation Program Modeling System) of the US Environmental Protection Agency. In addition, the Neural Network MATLAB Toolbox was utilized for data analysis. WASP was able to accurately simulate the water hydrodynamics and coliform concentrations within the North Fork, while the neural network assisted in identifying correlations between fecal coliform and the various parameters involved. The numerical results supported the conclusion that fecal coliform were introduced by the animal populations along the riverbanks and by storm water washout of the adjacent drainage basins and the banks. The problem is exaggerated due to the low flashing capacity of the river.