scholarly journals The development of a pulsating supraglacial stream

2016 ◽  
Vol 57 (72) ◽  
pp. 31-38 ◽  
Author(s):  
S. L. ST. Germain ◽  
B. J. Moorman
Keyword(s):  
Pulsating Flow ◽  
Rainfall Events ◽  
High Discharge ◽  
Stream Discharge ◽  
Rapid Changes ◽  
Hydrological System ◽  
Meander Bends ◽  
Pool Formation ◽  
Transverse Fractures ◽  
Shear Planes

ABSTRACTSupraglacial streams are a significant part of the glacial hydrological system and important for understanding the connection between glacial hydrology and glacier dynamics. Here we determine the factors that influence the development of step-pool formation and pulsating flow in a supraglacial stream on Bylot Island, Nunavut. Results show that during the second week of a 2-week study, multiple successive rainfall events occurred, stream temperature increased and ablation decreased; which also caused stream discharge to decrease. In addition, the stream, which flowed over a 13 m high waterfall off the front of Fountain Glacier, rapidly formed 21 step-pools and began to pulsate. The pulsating phenomenon involved the complete stoppage of flow over the waterfall and the subsequent restart between 8 and 20 s later. Pulsating flow resulted from rapid changes in the streambed morphology. In particular, the formation of the step-pool sequence was caused by helical flow around meander bends and hydrologically induced slippage along transverse shear planes, evidenced by observations of high-pressure artesian flow from transverse fractures. Contrary to previous literature, this study shows that high discharge is not necessarily the cause of step-pool formation and pulsating flow within supraglacial streams.

scholarly journals Assessing methods for the estimation of response times of stream discharge: the role of rainfall duration

2019 ◽  
Vol 67 (2) ◽  
pp. 143-153 ◽  
Author(s):  
Jaime G. Cuevas ◽  
José L. Arumí ◽  
José Dörner
Keyword(s):  
Response Times ◽  
Stream Velocity ◽  
Middle Point ◽  
Rainfall Events ◽  
Average Value ◽  
Stream Discharge ◽  
Rainfall Duration ◽  
Watershed Dynamics ◽  
The Mean

Abstract Lagtimes and times of concentration are frequently determined parameters in hydrological design and greatly aid in understanding natural watershed dynamics. In unmonitored catchments, they are usually calculated using empirical or semiempirical equations developed in other studies, without critically considering where those equations were obtained and what basic assumptions they entailed. In this study, we determined the lagtimes (LT) between the middle point of rainfall events and the discharge peaks in a watershed characterized by volcanic soils and swamp forests in southern Chile. Our results were compared with calculations from 24 equations found in the literature. The mean LT for 100 episodes was 20 hours (ranging between 0.6–58.5 hours). Most formulae that only included physiographic predictors severely underestimated the mean LT, while those including the rainfall intensity or stream velocity showed better agreement with the average value. The duration of the rainfall events related significantly and positively with LTs. Thus, we accounted for varying LTs within the same watershed by including the rainfall duration in the equations that showed the best results, consequently improving our predictions. Izzard and velocity methods are recommended, and we suggest that lagtimes and times of concentration must be locally determined with hyetograph-hydrograph analyses, in addition to explicitly considering precipitation patterns.

scholarly journals Biotic controls on solute distribution and transport in headwater catchments

2015 ◽  
Vol 12 (1) ◽  
pp. 213-243 ◽  
Author(s):  
E. M. Herndon ◽  
A. L. Dere ◽  
P. L. Sullivan ◽  
D. Norris ◽  
B. Reynolds ◽  
...  
Keyword(s):  
Organic Matter ◽  
Stream Water ◽  
Solution Chemistry ◽  
Pore Waters ◽  
Rainfall Events ◽  
Headwater Catchments ◽  
Stream Discharge ◽  
Weak Complexes ◽  
Concentration Behavior ◽  
Shale Hills

Abstract. Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of headwater catchments underlain by shale in Pennsylvania, USA (Shale Hills) and Wales, UK (Plynlimon), dissimilar concentration-discharge behaviors are best explained by contrasting landscape distributions of soil solution chemistry – especially dissolved organic carbon (DOC) – that have been established by patterns of vegetation. Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heterogeneous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic "bioactive" behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where soil organic matter (SOM) is dominantly in lowlands (e.g., Shale Hills), bioactive elements are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), bioactive elements are released later during rainfall events. The distribution of vegetation and SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments.

Rainfall events and downstream drift of microcrustacean zooplankton in a Newfoundland boreal stream

2002 ◽  
Vol 80 (6) ◽  
pp. 997-1003 ◽  
Author(s):  
Christine E Campbell
Keyword(s):  
Invertebrate Drift ◽  
Zooplankton Abundance ◽  
Strongly Correlated ◽  
Upstream Site ◽  
Rainfall Events ◽  
Flushing Rate ◽  
Stream Discharge ◽  
Stream Productivity ◽  
High Precipitation ◽  
Zooplankton Drift

While rainfall events may lead to flushing of zooplankton from lakes, with implications for stream productivity near lake outlets, consideration also needs to be given to zooplankton transported farther downstream. To evaluate such downstream transport, daytime invertebrate drift, stream discharge, and rainfall events were monitored over 4 summers in Cook's Brook, Newfoundland, at a downstream site 1.0 km below the outlet of Big Cook's Pond and an upstream site 1.0 km upstream of the pond. Microcrustacean zooplankton were abundant in some downstream samples; high percent zooplankton abundance (87–94%) corresponded to the highest total invertebrate drift densities. Percent zooplankton in downstream drift was strongly correlated with recent rainfall (rS = 0.815, p = 0.025) and stream discharge (rS = 0.964, p = 0.001). The majority of microcrustaceans in the drift were planktonic cladocerans and copepods, the species composition being similar to that in Big Cook's Pond. No zooplankton were ever collected from the upstream site. Ephemeroptera, Diptera, Trichoptera, and Ostracoda were abundant in most drift samples. Zooplankton drift (mean = 0.17 individuals/m3) in Cook's Brook appears to be catastrophic drift, with high precipitation rates and resultant increased flushing rate in Big Cook's Pond leading to "washout" of microcrustaceans 1 km downstream.

scholarly journals A coupled modeling framework of the co-evolution of humans and water: case study of Tarim River Basin, western China

2014 ◽  
Vol 11 (4) ◽  
pp. 3911-3966
Author(s):  
D. Liu ◽  
F. Tian ◽  
M. Lin ◽  
M. Sivapalan
Keyword(s):  
Vegetation Cover ◽  
Natural Vegetation ◽  
Western China ◽  
Tarim River ◽  
Tarim River Basin ◽  
Coupled Modeling ◽  
Modeling Framework ◽  
Stream Discharge ◽  
Hydrological System ◽  
Crop Area

Abstract. The complex interactions and feedbacks between humans and water are very essential issues but are poorly understood in the newly proposed discipline of socio-hydrology (Sivapalan et al., 2012). An exploratory model with the appropriate level of simplification can be valuable to improve our understanding of the co-evolution and self-organization of socio-hydrological systems driven by interactions and feedbacks operating at different scales. In this study, a simple coupled modeling framework for socio-hydrology co-evolution is developed for the Tarim River Basin in Western China, and is used to illustrate the explanatory power of such a model. The study area is the mainstream of the Tarim River, which is divided into two modeling units. The socio-hydrological system is composed of four parts, i.e. social sub-system, economic sub-system, ecological sub-system, and hydrological sub-system. In each modeling unit, four coupled ordinary differential equations are used to simulate the dynamics of the social sub-system represented by human population, the economic sub-system represented by irrigated crop area, the ecological sub-system represented by natural vegetation cover and the hydrological sub-system represented by stream discharge. The coupling and feedback processes of the four dominant sub-systems (and correspondingly four state variables) are integrated into several internal system characteristics interactively and jointly determined by themselves and by other coupled systems. For example, the stream discharge is coupled to the irrigated crop area by the colonization rate and mortality rate of the irrigated crop area in the upper reach and the irrigated area is coupled to stream discharge through irrigation water consumption. In a similar way, the stream discharge and natural vegetation cover are coupled together. The irrigated crop area is coupled to human population by the colonization rate and mortality rate of the population. The inflow of the lower reach is determined by the outflow from the upper reach. The natural vegetation cover in the lower reach is coupled to the outflow from the upper reach and governed by regional water resources management policy. The co-evolution of the Tarim socio-hydrological system is then analyzed within this modeling framework to gain insights into the overall system dynamics and its sensitivity to the external drivers and internal system variables. In the modeling framework, the state of each subsystem is holistically described by one state variable and the framework is flexible enough to comprise more processes and constitutive relationships if they are needed to illustrate the interaction and feedback mechanisms of the human–water system.

Low productivity of Chinook salmon strongly correlates with high summer stream discharge in two Alaskan rivers in the Yukon drainage

2015 ◽  
Vol 72 (8) ◽  
pp. 1125-1137 ◽  
Author(s):  
Jason R. Neuswanger ◽  
Mark S. Wipfli ◽  
Matthew J. Evenson ◽  
Nicholas F. Hughes ◽  
Amanda E. Rosenberger
Keyword(s):  
Chinook Salmon ◽  
Oncorhynchus Tshawytscha ◽  
Population Declines ◽  
Environmental Predictors ◽  
High Discharge ◽  
Stream Discharge ◽  
Yukon River ◽  
Stock Recruitment ◽  
Sources Of Variation ◽  
Major Floods

Yukon River Chinook salmon (Oncorhynchus tshawytscha) populations are declining for unknown reasons, creating hardship for thousands of stakeholders in subsistence and commercial fisheries. An informed response to this crisis requires understanding the major sources of variation in Chinook salmon productivity. However, simple stock–recruitment models leave much of the variation in this system’s productivity unexplained. We tested adding environmental predictors to stock–recruitment models for two Yukon drainage spawning streams in interior Alaska — the Chena and Salcha rivers. Low productivity was strongly associated with high stream discharge during the summer of freshwater residency for young-of-the-year Chinook salmon. This association was more consistent with the hypothesis that sustained high discharge negatively affects foraging conditions than with acute mortality during floods. Productivity may have also been reduced in years when incubating eggs experienced major floods or cold summers and falls. These freshwater effects — especially density dependence and high discharge — helped explain population declines in both rivers. They are plausible as contributors to the decline of Chinook salmon throughout the Yukon River drainage.

scholarly journals Landscape heterogeneity drives contrasting concentration–discharge relationships in shale headwater catchments

2015 ◽  
Vol 19 (8) ◽  
pp. 3333-3347 ◽  
Author(s):  
E. M. Herndon ◽  
A. L. Dere ◽  
P. L. Sullivan ◽  
D. Norris ◽  
B. Reynolds ◽  
...  
Keyword(s):  
Organic Matter ◽  
Landscape Heterogeneity ◽  
Stream Water ◽  
Solution Chemistry ◽  
Pore Waters ◽  
Rainfall Events ◽  
Headwater Catchments ◽  
Stream Discharge ◽  
Concentration Behavior ◽  
Shale Hills

Abstract. Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of three shale-underlain headwater catchments located in Pennsylvania, USA (the forested Shale Hills Critical Zone Observatory), and Wales, UK (the peatland-dominated Upper Hafren and forest-dominated Upper Hore catchments in the Plynlimon forest), dissimilar concentration–discharge (C–Q) behaviors are best explained by contrasting landscape distributions of soil solution chemistry – especially dissolved organic carbon (DOC) – that have been established by patterns of vegetation and soil organic matter (SOM). Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heterogeneous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Furthermore, concentration–discharge relationships of non-chemostatic solutes changed following tree harvest in the Upper Hore catchment in Plynlimon, while no changes were observed for chemostatic solutes, underscoring the role of vegetation in regulating the concentrations of certain elements in the stream. These results indicate that differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where SOM is dominantly in lowlands (e.g., Shale Hills), we infer that non-chemostatic elements associated with organic matter are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), these non-chemostatic elements are released later during rainfall events. The distribution of SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments.

Economic Way of Thought and Legislationon Nonprofit Organizations

2012 ◽  
pp. 48-63
Author(s):  
L. Yakobson
Keyword(s):  
Nonprofit Organizations ◽  
Empirical Data ◽  
Nonprofit Sector ◽  
Social Medium ◽  
The State ◽  
Rapid Changes ◽  
Comparative Advantages ◽  
Essential Prerequisite

The article considers proper legislation as an essential prerequisite for actualization of NPOs comparative advantages. Restrictions imposed on NPOs are reasonable if they are compensated by benefits from greater trust. The rigidity of constrains and requirements should be optimized while accounting for peculiarities of a social medium, the state of the nonprofit sector, and the governments readiness to encourage the development of the latter. As empirical data suggests, Russian NPOs being on different stages of maturity need separate legal treatment. In the meanwhile, interests that prevail in the NPOs community are not always conducive to rapid changes.

Section 6.a Introduction

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Rebecca PRICE ◽  
Christine DE LILLE ◽  
Cara WRIGLEY ◽  
Kees DORST
Keyword(s):  
Case Studies ◽  
Organizational Leadership ◽  
Research Community ◽  
Design Management ◽  
Management Research ◽  
Research Methodologies ◽  
Organizational Research ◽  
Research Perspectives ◽  
Rapid Changes

There is an increasing need for organizations to adapt to rapid changes in society. This need requires organizations’ and the leader within them, to explore, recognize, build and exploit new capabilities. Researching such capabilities has drawn attention from the design management research community in recent years. Dominantly, research contributions have focused on perspectives of innovation and the strategic application of design with the researcher distanced from context. Descriptive and evaluative case studies of past organizational leadership have been vital, by building momentum for the design movement. However, there is a need now to progress toward prescriptive and explorative research perspectives that embrace context through practice and the simultaneous research of design.  Therefore, the aim of this track is to lead and progress discussion on research methodologies that support the research community in developing explorative and prescriptive research methodologies for context-orientated organizational research. This track brings together a group of diverse international researchers and practitioners to fuel discussion on design approaches and subsequent outcomes of prescriptive and explorative research methodologies.

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