Browsing by Author "Li, Ming-Han"
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Item Aging effects of environmental factors on rolled erosion control products(Texas A&M University, 2007-04-25) Khanna, SumeeThis thesis presents a study made on erosion control blankets with respect to their aging and longevity. Erosion control blankets have been relied upon increasingly in recent times replacing the old and traditional methods for protecting areas from erosion by storm water and other factors. But what can be an estimated duration for which a given set of blankets can be functional in channel erosion control. This research is done with the ultimate aim of understanding whether these erosion control blankets can stay in place and be conducive to some vegetation growth, which is said to be the most reliable measure for long-lasting erosion control. Seven erosion control blankets, consisting of natural, synthetic and composite types, were put to actual use for erosion control for 3 years in a field. After 3 years these used materials were cut from the field for conducting the tests. Unused blankets of the same brands were obtained. Index tests were conducted on both used and unused material specimens to measure the erosion control properties. All materials experienced a significant amount of strength loss after use. The natural materials show 80% strength loss, while the composite and synthetic materials were tested to have around 50% strength losses after being put to use for 3 years. Thus it can be observed that the composite and synthetic materials have a decent amount of life where erosion control is concerned. Other tests also proved that composite materials can be relied upon for erosion control to a reasonable extent, and the research goal was achieved.Item Connecting Land Use and Transportation Toward Sustainable Development: A Case Study of Houston-Galveston Metropolitan Area(2011-02-22) Lee, Jae SuHow do land use characteristics affect individual and household travel behavior in a regional context? Can the investigation justify the land use policies to reduce automobile dependence and achieve the goals of sustainable development in the metropolitan areas? Previous research enhanced our understanding of the connections between land use and travel behavior. It also provided implications for managing automobile-dependent travel behavior. However, there are questions still left unanswered about the causal connections between them, and the effectiveness of the land use policies to manage travel demand. To address the issues, attention is focused on the effects of land use measures on travel behavior outcomes from different modeling perspectives. The travel demand modeling explores the associations between land use and travel behavior. In addition, the causal modeling helps clarify the causal connections between them. It includes the structural equation models (SEMs) and the directed acyclic graphs (DAGs). The study focuses on six counties of the Houston-Galveston Area Council (HGAC) area. Travel behavior outcomes contain individual mode choice, household automobile trip generation and household total vehicle miles traveled (VMT). Three dimensions (i.e., density, diversity and design) of six land use measures are considered, which are computed using quarter-mile buffers for both trip origins and destinations. Different travel outcomes and modeling strategies are examined for different travel purposes. The significance of land use measures in affecting travel behavior is found to be evident, while varying to a certain degree according to trip purposes, travel outcomes and methodologies. For individual model choice, multinomial logit (MNL) models, the SEMs and the DAGs for different trip purposes support the hypothesis that land use measures directly affect individual mode choice behavior when other factors are kept constant. There is also evidence from causal models that land use factors indirectly influence it through travel time. For household automobile trip generation, there is no evidence to assert that land use measures at origin significantly affect household automobile trip rates when travel cost and socioeconomic variables are controlled. However, it is confirmed that land use measures have indirect causal connections with automobile trips through travel costs for all trip purposes. For household total VMT, it is found that land use patterns around residential locations are not only significantly associated, but also causally connected with household VMT. To summarize, compact development with high density and improved network design generally contribute to the reduction in automobile dependent travel patterns in the HGAC region.Item Ecohydrological Planning for The Woodlands: Lessons Learned After 35 Years(2010-10-12) Yang, BoThe Woodlands, Texas, is a 27,000-acre new town created with Ian McHarg's ecohydrological planning approach. The Woodlands is the best example of ecologically based new town planning in the United States during the 1970s. The Woodlands survived storms in excess of one-hundred-year levels in 1979 and 1994 with little property damage, while Houston, 31 miles away, was severely flooded in both events. For the past three decades, very few studies have been conducted to assess the effectiveness of McHarg's planning approach. The objective of this study is three fold: (1) To document McHarg's ecohydrological planning concepts, implementation and unveil the barriers to continue his approach; (2) To compare flood mitigation effectiveness of different drainage systems used in The Woodlands development; and (3) To simulate "what if" land-use scenarios using different planning approaches. Original development information is collected from published monographs, journal articles, newspapers and designers' collections. Geographic Information System (GIS) parcel data are obtained from Montgomery County Appraisal District. Streamflow data are acquired from the USGS website. Weather data are downloaded from the NOAA website. Land use and land cover data are collected from various national datasets. Two GIS hydrologic models--the Soil and Water Assessment Tool (SWAT) and the Kinematic Runoff and Erosion model (KINEROS)--are used for watershed simulation. The statistic analysis tool SPSS is used for correlation analysis. Results show that McHarg's planning approach was followed in the early phases of development (1974-1996) but was largely abandoned in the later phases when its ownership was changed in 1997. McHarg's approach ceased to be implemented because of the low public acceptance of ecohydrological planning strategies and the conflicts between short-term investment return and long-term environmental stewardship. In addition, comparative study shows that the early phases of development responded to rainfall similarly to its pre-development forest conditions. However, the later phases generated runoff volumes three times greater than the early phases. Therefore, McHarg's ecohydrological planning approach demonstrates flood mitigation effectiveness that is superior to the conventional approach. Finally, using soil permeability to coordinate development density and land use presents a viable solution for mitigating environmental impacts from a stormwater perspective.Item Enhancing Quantification of a Landscape Project?s Environmental, Economic and Social Benefits: A Study of Landscape Architecture Foundation?s Landscape Performance Series(2014-11-26) Luo, YiLandscape performance is a newly initiated effort to evaluate the outcomes of landscape solutions in constructed projects. Built upon the sustainability triad, the outcomes landscape performance attempts to measure consists of environmental, economic and social aspects. These outcomes are collected and used to guide future design. The primary purpose of this study is to enhance landscape performance measurement to better inform future decision making. To achieve this goal, I took a four step approach: 1) reviewing performance measurement in four design disciplines to learn experiences from other disciplines and provide recommendations for landscape performance measurement, 2) studying current published case studies to identify gaps in the current landscape performance quantification practices, 3) analyzing the currently used landscape metrics and methods to identify gaps, and providing recommendations for future improvement, and 4) integrating costs into the framework of landscape performance quantification and exploring economic evaluation methods to valuing non-market landscape performance benefits to facilitate cost-benefit analysis of sustainable solutions. The results show that compared to previous performance measurements and rating systems, landscape performance is the only one with a framework that addresses the three aspects of sustainability. Its framework uses practices to guide research and simultaneously uses research results to inform practices. It has a good potential of collecting evidence for sustainable solutions and promoting measureable sustainable landscape practices. However, since landscape performance research is still new, it has a number of gaps, such as insufficient social and economic benefit quantification, insufficient cost consideration, and a lack of core prototype measuring methods and explicitly defined performance benchmarks. These gaps undermine credibility of landscape performance results and restrict its contribution to future decision making. This study helps fill these gaps by providing a number of recommendations, such as developing performance benchmarks for typical landscape solutions, developing robust core measuring systems to facilitate efficient data collection and quantification, and developing sample questionnaires to help with social benefits quantification. The significance of this study is that it will enhance the framework of landscape performance quantification, clarify cost embedded benefits of sustainable solutions, and promote sustainable landscape design practices.Item Hydrologic and Ecological Effects of Watershed Urbanization: Implication for Watershed Management in Hillslope Regions(2011-08-08) Sung, Chan YongIn this study, I examined the effect of watershed urbanization on the invasion of alien woody species in riparian forests. This study was conducted in three major steps: 1) estimating the degree of watershed urbanization using impervious surface maps extracted from remote sensing images; 2) examining the effect of urbanization on hydrologic regime; and 3) investigating a relationship between watershed urbanization and ecosystem invasibility of a riparian forest. I studied twelve riparian forests along urban-rural gradients in Austin, Texas. Hydrologic regimes were quantified by transfer function (TF) models using four-year daily rainfall-streamflow data in two study periods (10/1988-09/1992 and 10/2004-09/2008) between which Austin had experienced rapid urbanization. For each study period, an impervious surface map was generated from Landsat TM image by a support vector machine (SVM) with pairwise coupling. SVM more accurately estimated impervious surface than other subpixel mapping methods. Ecosystem invasibilities were assessed by relative alien cover (RAC) of riparian woody species communities. The results showed that the effects of urbanization differ by hydrogeologic conditions. Of the study watersheds, seven located in a hillslope region experienced the diminishing peakflows between the two study periods, which are contrary to current urban hydrologic model. I attributed the decreased peakflows to land grading that transformed a hillslope into a stair-stepped landscape. In the rest of the watersheds, peakflow diminished between the two study periods perhaps due to the decrease in stormwater infiltration and groundwater pumpage that lowered groundwater level. In both types of watersheds, streamflow rising during a storm event more quickly receded as watershed became more urbanized. This study found a positive relationship between RAC and watershed impervious surface percentage. RAC was also significantly related to flow recession and canopy gap percentages, both of which are indicators of hydrologic disturbance. These results suggest that urbanization facilitated the invasion of alien species in riparian forests by intensifying hydrologic disturbance. The effects of urbanization on ecosystems are complex and vary by local hydrologeologic conditions. These results imply that protection of urban ecosystems should be based on a comprehensive and large-scale management plan.Item Urban Form and Travel Patterns at the Regional Scale Considering Polycentric Urban Structure(2012-10-19) Yi, Young-JaeIncreasing concerns about climate change have attracted global interests in reducing auto travel. Regional average vehicle miles traveled (VMT) vary across the urbanized areas in the U.S., suggesting a potential influence of development patterns on greenhouse gas emission. To explore the contribution of development control to driving reduction at the regional scale, this dissertation estimated impacts of urban form on two travel outcomes at the metropolitan scale: daily vehicle miles traveled (DVMT) per capita and daily transit passenger miles (DPMT) per capita. To overcome major problems of previous studies, i.e., lack of generalizability and multicollinearity, a cross-sectional analysis of 203 U.S. urbanized areas was conducted, using directed acyclic graph and structural equation modeling. A literature review revealed gaps in the previous research: while individual-level behavioral studies have identified distance from the center as the most influential factor on VMT, regional-level studies have not reflected this relationship and failed to deliver effective implications for land use policies. A method to identify regional centers was evaluated to appropriately measure polycentric urban structure of contemporary metropolitan areas. The evaluation found that lower density cutoff, wider reference area, and equal treatment between central business district (CBD) and subcenters yielded better performance in McMillen's two-stage nonparametric method. Results also showed that for polycentric areas, the use of a polycentric model produced a better model fit than the monocentric model. Major findings of this dissertation include 1) higher regional concentration, greater local density and less road supply per capita lowered VMT, and 2) higher local density and more transit supply per capita increased PMT. These results imply that different approaches to development control are needed for different sustainable transportation goals - intensifying regional centers such as infill developments for VMT reduction, and compact neighborhood development approaches, such as transit oriented development for transit promotion. However, CBD has a limited capacity and indiscreet compact developments at the urban fringe can lead to decentralization from the regional perspective, and consequently result in increased VMT. This study suggests polycentricism as a potential solution for the contradictive development principle. By allowing dispersion and concentration at the same time, urban form control at the regional level will be more beneficial than conventional local-level control.