The spatial distribution of imperviousness in watershed hydrology

Mejia, Alfonso I University of Maryland, College Park 2009 해외박사(DDOD)

Urbanization affects the hydrology of watersheds often leading to increases in runoff volumes and peak flows. These impacts are mainly attributed to the presence of imperviousness on the landscape which inhibits the soil infiltration process. Normally, these impacts are studied at the hillslope scale and under lumped watershed conditions. The impacts at the watershed scale under more spatially distributed conditions have been studied less. Advancements in spatial observations and techniques, distributed hydrologic modeling, and greater understanding of the importance of scale in hydrology have increased the feasibility and need for including spatial data sets and methods into hydrologic investigations. This dissertation focuses on understanding the role and importance of the spatial distribution of imperviousness in watershed hydrology. The spatial distribution of imperviousness is investigated by incorporating various spatial datasets, techniques, and modeling approaches that are used routinely for the hydrology of natural watersheds but less frequently for urbanized conditions. The distribution of imperviousness is investigated based on three approaches. The first approach uses optimization concepts to study where imperviousness can be placed in the watershed to reduce negative impacts on flooding. The second approach develops, implements, and tests a hydrologic event-based model to study the influence of the spatial distribution of imperviousness on the hydrologic response. The last approach relates analytically the space-time variability of rainfall, runoff, and the routing process to the imperviousness pattern, and synthesizes the complex space-time variations into a simpler framework. From the first approach distinct patterns of imperviousness were obtained that embodied water resources objectives. For example, the clustering of imperviousness along the main channel was found to globally reduce peak flows along the stream network. The second approach indicated that the overall imperviousness pattern can have a considerable impact on the hydrologic response. The last approach showed that the spatial patterns of rainfall and imperviousness can interact to increase or decrease the average amount of rainfall excess. The main contribution from this research is a larger understanding of the role of the spatial distribution of imperviousness in watershed hydrology. It also demonstrates the usefulness of applying hydrologic knowledge of natural watersheds to anthropogenically-altered watersheds.

Process-based characterization of near-surface hydrologic response and hydrologically driven slope instability

Ebel, Brian A Stanford University 2007 해외박사(DDOD)

This dissertation employs numerical simulation of 3D variably-saturated hydrologic response, using the Integrated Hydrology Model (InHM), to investigate hydrologically-driven slope failure at the field scale for the well-studied Coos Bay experimental catchment (CB1) in the Oregon Coast Range. The first phase of this study analyzes the extensive hydrologic-response observations and site characterization from three sprinkling experiments to establish the boundary-value problem (BVP) for InHM simulations at CB1. In the second phase of this effort, the BVP from the first phase is employed to simulate fluid flow and deuterium transport for the three CB1 sprinkling experiments. Model performance is evaluated using the integrated (i.e., discharge and deuterium concentrations in discharge) and distributed (i.e., pressure head, soil-water content, and deuterium concentrations) hydrologic response. The third phase of this study assesses the uniqueness of the InHM BVP using continuous simulation of seven years of hydrologic response from 1990-1996. Sensitivity analyses for the InHM BVP for CB1 are conducted and used to improve the BVP uniqueness relative to simulation of larger magnitude storms where slope failure potential is higher. In the fourth phase of this effort, equally defendable BVP scenarios are used to evaluate uncertainty in the simulated hydrologic response during the storm that caused the 1996 CB1 slope failure. Infinite slope stability assessments are used to evaluate slope stability. The major conclusions from this study include the importance of (i) layered geologic interfaces comprising permeability contrasts, (ii) fracture flow through weathered and unweathered rock, (iii) deeper water table position and interaction with the near-surface, and (iv) representation of hysteretic characteristic curves in physically-based simulation of hydrologic response related to slope instability. This study also demonstrates, for both event-based and continuous hydrologic-response simulation, that accurate simulation of an integrated hydrologic response is no guarantee that the distributed hydrologic response is of equal accuracy. The analyses presented here indicate that uniqueness is a problem for hydrologically-driven slope failure simulation when a BVP used successfully to simulate lower intensity storms is employed for larger storms with a higher potential for slope failure.

Regional scale landscape evolution: Physics-based simulation of hydrologically-driven surface erosion

Ran, Qihua Stanford University 2006 해외박사(DDOD)

The effort reported in this dissertation was motivated by the fact that, to the best of my knowledge, no comprehensive physics-based hydrologic-response model has been employed to investigate landscape evolution at a scale larger than a single catchment. Neglecting surface/near-surface hydrologic-response and sediment-transport processes at large scales hinders our understanding of landscape evolution. The Integrated Hydrology Model (InHM) was used in this study to simulate long-term hydrologic response at the regional scale. A sediment transport algorithm was developed and added to InHM for this study to simulate long-term erosion and deposition at the regional scale. The Hawaiian Island of Kaho'olawe was selected as the application site for this study. The major objective of this study was to demonstrate that a comprehensive physics-based hydrologic-response model could be used to investigate hydrologically-driven surface erosion at the regional scale. Long-term (100 years) rainfall data were generated to drive the hydrologic-response and sediment-transport simulations for Kaho'olawe. It was not possible to simulate the entire island as a single large boundary-value problem (BVP) due to available computer resources. Therefore, the island was divided into 84 catchments and the simulations were conducted one catchment at a time. For this study, land-use management impacts were represented by the variability in the near-surface soil-hydraulic property values (e.g., saturated hydraulic conductivity). The regional-scale long-term physics-based hydrologic-response and sediment-transport simulations conducted in this study were successful. The simulation results show that the three primary conditions affecting the generation of runoff and erosion for Kaho'olawe were (i) soil-hydraulic parameters, (ii) surface slope, and (iii) vegetation. Land-use management affects runoff and erosion by changing the surface condition and the near-surface soil properties. Sensitivity analysis illustrates that the rainfall timestep, the horizontal discretization, the near-surface soil-hydraulic parameters, and evapotranspiration each have a significant impact on simulated runoff and erosion. An extension of this study would be to formulate InHM for a Unix/Linux platform so that large-scale problems, with small discretization, could be considered (e.g., simulate Kaho'olawe as a single large detailed BVP).

Spatial and temporal relations between soil processes, morphology, and hydrology in Minnesota landscapes

Reuter, Ronald Joseph University of Minnesota 1999 해외박사(DDOD)

The combination of topography and soil properties, such as hydraulic conductivity and texture, control the movement of water within a landscape. Research in pedology has shown that the movement of water and long-term average location of the water table is recorded in the soil morphology. The objective of this research was to quantify the relationships between hydrology and soil morphology for three landscape types in Minnesota. Three study sites, located in northwest, east-central, and southern Minnesota were instrumented to monitor location of the near-surface aquifer, soil temperature, soil water tension, and redox potential. Soils were described and sampled for morphological properties, including organic matter content, pH, and Fe and Al content. Monitoring data was used to determine the influence of current hydrology and environmental factors on the distribution of soil morphological properties. Terrain attributes were used to model the distribution of hydric soils at the southern site. A Saturation Temperature Index (STI) was developed from the northwest site data as a measure of potential development of hydromorphic soils. The distribution of redoximorphic features along the hillslope at the east-central site was not related to current hydrology. However, the distribution of Fe in soil profiles along the hillslope and locations of Fe-dominated spodic materials suggested that the morphology is reflective of both past and present water levels. The soils and monitoring data at the southern site best support the hypothesis that distribution of morphology is controlled by landscape hydrology. The Profile Darkness Index (PDI), which is correlated with landscape position and organic matter content, was highly correlated with duration of saturation (r<super>2</super> = 0.77) and STI (r<super>2</super> = 0.93) at the southern site, indicating a quantifiable relationship between hydrology and morphology. This site is a mix of open and closed drainage watersheds. Distribution of hydric soils had high agreement (74%) with the terrain attribute model in the open-drainage areas but only 52% agreement in areas with closed drainage. Overall, the results of this research indicate that landscape hydrology is in part controlled by the combination of topography and soil properties and results in a characteristic distribution of soil morphology.

How does runoff begin (and end)?

Mirus, Benjamin B Stanford University 2009 해외박사(DDOD)

The question of how surface water channels begin is a long standing problem in hydrology and geomorphology. Because the depth/velocity of surface runoff is the driving force behind erosion and sediment transport, understanding the complex dynamics associated with spatially and temporally variable hydrologic-response is necessary. The objective of this work is to quantitatively characterize the controls on the location and timing of runoff. A heuristic, simulation-based approach is employed to examine the thresholds between different runoff-generation mechanisms. At the heart of this effort is a comprehensive, physically-based hydrologic-response model (InHM) and datasets from four well-characterized catchments (C3, TW, R5, and CB). The C3 and CB catchments are located within steep, forested terrain; the TW and R5 catchments are located in gently sloping rangeland. The datasets are sufficient to parameterize and evaluate four base-case boundary-value problems (BVP). Each base-case BVP provides an acceptable simulation of the observed hydrologic response. The base cases are reduced to basic-case scenarios, which share a common level of BVP complexity and capture the overall hydrologic-response processes of the corresponding base case. The four basic cases provide the corner-stones for alternative hypothetical-reality simulation scenarios designed to address the question of how runoff begins (and ends). The concept-development simulations (event-based and continuous) were conducted in three phases to examine: (i) soil-hydraulic properties, (ii) rainfall characteristics, and (iii) important BVP characteristics identified in the preceding phases. The simulation results facilitate quantitative analysis of both integrated and distributed hydrologic response at high spatial and temporal resolution over a wide range of conditions. The results from 160 unique simulation scenarios illustrate how rainfall intensity/depth, subsurface permeability contrasts, characteristic curve shapes, and topography provide important controls on the hydrologic-response dynamics. The processes by which channelized runoff begins (and ends) are shown, in large part, to be defined by the relative rates of infiltration and the convergence of lateral drainage from the variably-saturated soil layers.

Hydrologic response in small urban watersheds: Analyses from the Baltimore Ecosystem Study

Meierdiercks, Katherine L Princeton University 2009 해외박사(DDOD)

Flooding in urban environments represents a major societal hazard, especially as the world's population rapidly concentrates in urban regions. In this dissertation hydrologic, hydraulic, and hydrometeorological processes that control flooding in urban environments are examined through empirical analyses and numerical modeling studies centered on the study watersheds of the Baltimore Ecosystem Study (BES), a component of the National Science Foundation's Long Term Ecological Research (LTER) network. The BES watersheds exhibit contrasting patterns and histories of development; the Gwynns Falls watershed, and its Dead Run tributary, are the principal study regions for this work. Central research contributions of this study are closely linked to a series of field campaigns in the Dead Run watershed during the warm seasons (June--August) of 2003, 2004, and 2005. Hydrologic, hydraulic, and urban infrastructure data sets, developed as part of the 2003--2005 field campaigns, play a central role in this dissertation and represent an important contribution to urban hydrology. Urban flood studies have linked the severity of flooding to the percent imperviousness of a watershed. In this dissertation, it is shown that, in many settings, stormwater management infrastructure plays a larger role in determining urban flood response than impervious fraction. A particular focus of this study is the urban drainage network, which can include storm drain pipes, surface channels, and street gutters. It is shown that urban drainage networks, like natural river networks, exhibit characteristic structures and that these features, along with stormwater detention infrastructure, play critical roles in determining urban flood response. It is also shown that rainfall variability at time scales shorter than 15 minutes and spatial scales finer than 1 km are central elements of urban flood response. Rainfall analyses combine storm total observations from a dense rain gage network deployed for the 2003--2005 field campaigns and radar rainfall estimates derived from multiple radars in the Baltimore metropolitan region. Hydrologic modeling studies utilize the Environmental Protection Agency's Stormwater Management Model (SWMM), which provides a flexible platform for examining the impacts of urbanization on flood response. Striking heterogeneity of hydrologic response in the Gwynns Falls watershed, associated with contrasting patterns and history of urban development, is characterized based on the 10-year BES observing record. A new framework for performing flood frequency analyses on a drainage network is introduced and illustrated through empirical and modeling applications in the Gwynns Falls and Dead Run watersheds. Case study analyses of extreme flooding in the Dead Run watershed illustrate the interplay of rainfall variability and urban infrastructure in determining the flood hazards of urban environments. Although analyses are focused on metropolitan Baltimore, they provide a general picture of the hydrologic, hydraulic and hydrometeorological controls of flooding in many urban settings.

Physics-based simulations of hydrologic-response and cumulative watershed effects

Carr, Adrianne Elizabeth Stanford University 2007 해외박사(DDOD)

This study quantitatively addresses, via simulation, the impacts of forest management practices on near-surface hydrologic response at the catchment and watershed scales. The simulations were conducted with the Integrated Hydrology Model (InHM) for the North Fork of Caspar Creek Experimental Watershed, located near Fort Bragg, California. InHM is a comprehensive physics-based hydrologic-response model. The North Fork watershed (including 11 tributary catchments) is the site of an ongoing study monitoring the impacts of forest practices. InHM was parameterized and calibrated using existing data and new field measurements of soil-hydraulic properties. The simulations were conducted for three wet seasons: before logging, after logging, and after a period of regrowth. The increases in throughfall and decreases in potential evapotranspiration related to timber harvesting had significant impacts on the simulated hydrologic response for the Caspar Creek catchments. The simulated increases in discharge depths and peak discharges were considerably higher after partial and full clearcut harvesting. Hypothetical-reality cumulative watershed effects (CWEs) simulations were carried out to examine potential impacts of alternative timber harvest levels and methods relative to these that occurred in the North Fork watershed. The results from these simulations show that the increases in the simulated discharge after clearcutting were significant for the catchment and watershed scales and that relatively small changes in soil-hydraulic properties produced substantial changes in the hydrologic response. The simulations in this study clearly illustrate that timber harvesting can alter the streamflow generation mechanisms and patterns within a given catchment. The effort reported here sets a firm foundation for investigating complex processes leading to CWEs, such as flooding, slope-stability, sediment transport, and their impacts on salmon habitat.

Eco-Hydrological Analysis of Wetlandscapes

Bertassello, Leonardo Enrico Purdue University ProQuest Dissertations & Theses 2019 해외박사(DDOD)

Wetlands are dispersed fractal aquatic habitats that play a key role in watershed ecohydrology. Wetlands provide critical habitats for specialized fauna and flora, process nutrients, and store water. Wetlands are found in a wide range of landscapes and climates, including humid/tropical regions where surface water is abundant, and in semiarid/arid regions with surface-water deficits. Wetland morphology and hydrology are governed by geomorphology and climate. Wetlands are dynamic; they change in space and time in response to unsteady external conditions, and over longer term to internal process feedbacks. Together, wetlands form a mosaic of heterogeneous, dynamic, aquatic habitats in varying spatial organizations, networked by hydrological and ecological connections.The overarching goal of the proposed research is to provide a robust theoretical framework to model the dynamics of multiple wetlands spread across watersheds (wetlandscape). In particular, the three main lens I used for identifying the spatiotemporal variability in wetlandscapes were: hydrology, morphology and ecology. Indeed, the hydrological modeling of wetlands is of key importance to determine which habitats are potentially able to host aquatic and semiaquatic species, as well as function as retention basin for storing considerable amount of water or for processing nutrients. Wetlands interaction with the landscape topography is essential to characterize the morphological attributes of these waterbodies. Different generating mechanisms have produced differences in wetland shapes and extent. However, even if wetlands are different among regions, and also within the same landscape, the set of function that they can support is similar. In the present research, I have also proposed that because water accumulates at low elevations, topography-based models helpful for the identification of wetlands in landscapes. These types of models are useful especially in those cases were wetlands data are sparse or not available. The proposed approaches could reproduce the abundance and distribution of active wetlands found in the NWI database, despite the differences in identification methods. In particular, I found that wetland size distributions in all the conterminous United States share the same Pareto pdf. Furthermore, the wetland shape is constrained into a narrow range of 2D fractal dimension (1.33;1.5). Since this method can be carried out with only a DEM as input, the proposed framework can be applied to any DEM to extract the location and the extent of depressional wetlands.Wetlands are among the most biologically diverse ecosystems, serving as habitats to a wide range of unique plants and animal life. In fact, wetlands and their surrounding terrestrial habitats are critical for the conservation and management of aquatic and semi-aquatic species. Understating the degree and dynamics of connectedness among individual wetlands is a challenge that unites the fields of ecology and hydrology. Connectivity among spatially distributed mosaic of wetlands, embedded in uplands, is critical for aquatic habitat integrity and to maintain metapopulation biodiversity. Land-use and climate change, among other factors, contribute to wetland habitat loss and fragmentation of dispersal networks. Here, I present an approach for modeling dynamic spatiotemporal changes, driven by stochastic hydroclimatic forcing, in topology of dispersal networks formed by connecting habitat zones within wetlands. I examined changes in topology of dispersal networks resulting from temporal fluctuations in hydroclimatic forcing, finding that optimal dispersal network are available only for limited time period, thus species need to constantly adapt to cope with adverse conditions.

Spatial and temporal patterns in high latitude hydrologic systems

Pavelsky, Tamlin Muir University of California, Los Angeles 2008 해외박사(DDOD)

Terrestrial water storage and transport are critical terms in the global water balance, yet they are poorly observed at high northern latitudes. An already sparse network of hydrologic monitoring stations has declined in recent years, coinciding with rapid changes associated with anthropogenic climate warming. New strategies are required to understand reservoirs and fluxes in the high-latitude hydrologic system. Field surveys, analysis of historical data, and remote sensing are deployed here to address questions in high-latitude hydrology. Eurasian river discharge to the Arctic Ocean has increased since 1936, but mechanism remains unknown due in part to uncertainties in precipitation data. Four gridded precipitation datasets are compared (two observational, two reanalysis) in 198 river basins between 1958 and 1989. Observational datasets outperform reanalysis products for the scales and time period examined. Comparison of precipitation and discharge trends over a longer period (66 basins, 1936-1999) suggests that precipitation accounts for half of observed discharge increases. As in situ measurements of discharge decline, new strategies are needed to monitor river flow. Remote sensing allows observation of variations in river width (often correlated with discharge), but automating extraction of width is nontrivial. RivWidth is a new software tool that automates the calculation of river flow width using raster-based classifications of inundation extent derived from remotely sensed imagery. It allows the rapid, accurate extraction of thousands of width values. Two summers (2006-2007) of field observations are combined with remotely sensed datasets to examine processes of hydrologic and sediment recharge in Canada's Peace-Athabasca Delta (PAD). Results suggest that existing theoretical models of floodplain recharge fail to capture observed patterns of inundation in the PAD. Instead, a dichotomy is found between the distributary channel network, which responds to summer high-water events, and floodplain lakes and wetlands, which do not. Robust positive relationships between in situ suspended sediment concentration (SSC) and remotely sensed visible/near-infrared reflectance in the PAD allow mapping of sediment transport and recharge processes. In addition, a first estimation of river flow velocity based on remotely-sensed SSC is presented. In sum, this study provides new insight on high-latitude hydrologic systems at continental, regional, and local scales.

Hydrologic modeling of irregular tile drainage systems

Garcia, Ana Maria University of Illinois at Urbana-Champaign 2001 해외박사(DDOD)

A physically-based flow model has been developed to specifically address the influence of irregular tile networks on Midwestern watershed hydrology. Several issues were identified as pertinent to this specific task: solving the problem of flow to a single tile drain, addressing irregular tile networks at the watershed scale and integrating the dominant hydrologic processes. An analytical solution to the problem of subsurface flow to a single tile was proposed and evaluated. This solution was incorporated into a description of infiltration which accounts for variable moisture conditions and complex precipitation patterns. Together, the tile flow solution and the comprehensive infiltration treatment constitute the subsurface flow component of the overall watershed-scale model. These account for the spatial conditions encountered at the field level, particularly the presence of tile lines which drain the soil profile and affect the subsurface water balance. The tile system and the stream channels in the watershed are modeled as one integrated directed network. The comprehensive network of links and nodes routes water that is drained by individual tile lines to the watershed outlet, yielding transient responses to precipitation along every node in the network. A grid-based description of the entire watershed served as a framework to integrate the subsurface module with the comprehensive directed network. The model was able to overcome the need to prescribe a spacing parameter for tile drainage and, therefore, is applicable to irregular tile drainage systems. When applied to a watershed in east-central Illinois (Upper Little Vermilion River watershed), the model was able to simulate observed trends, such as the minimal surface runoff and increased infiltration.