Browsing by Subject "Unpaved roads"
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Item Impacts of unpaved roads on runoff and sediment production in Culebra, Puerto Rico(2019-12) Mclaughlin, Preston Wyatt; Ramos-Scharrón, Carlos E.Terrigenous sediment delivery into tropical coastal waters from unpaved road development is a key stressor influencing the global decline of coral reef ecosystems. Higher turbidity of coastal waters from this terrigenous sediment can result in smothering, bleaching, and reduced photosynthetic activity for coral reefs. Since the 1990’s, the small Puerto Rican municipality of Culebra has experienced significant rates of land development, and an expansion of its unpaved road network, which has been identified as the contributing factor responsible for the continuous decline of the island’s live coral cover. This research focuses on quantifying runoff, and sediment production rates for Culebra’s unpaved road and undisturbed surfaces at the plot (~3 m²), and watershed (~1 km²) scales. A total of 46 rainfall-runoff simulations, and 119 Guelph permeamter tests were conducted to collect this data. Results indicate that only 1.2 mm of rainfall is required to produce overland flow on unpaved roads. At least 7.9 cm of rainfall is needed to generate overland runoff on undisturbed hillslopes. Erosion rates were greatest for recently graded road segments, with an average annual erosion rate of 54.65 Mg ha⁻¹ yr⁻¹. Unpaved roads that have been left ungraded for over one year erode at about half this rate (29 Mg ha⁻¹ yr⁻¹). Undisturbed surface erosion was negligible in comparison, with a mean rate of 0.05 Mg ha⁻¹ yr⁻¹. Based on this data, there are up to five orders of magnitude difference between erosion rates of graded unpaved roads and natural soil surfaces in Culebra. Within one year, a total of 335 storms occurred between. Around a quarter of all recorded storms produced overland runoff on unpaved road surfaces. Hurricane Maria was estimated to be the only storm that year to generate overland flow on undisturbed surfaces. ArcGIS was used to identify segments of road most likely to transport overland runoff to the coastline, as well as segments generating the most erosion. Sediment production rates for the study areas ranged between 3.1 and 10.9 Mg yr⁻¹. This information is beneficial towards documenting the overall effectiveness of erosion mitigation structures built to reduce terrigenous sediment transport produced from these roadsItem A Pavement Design and Management System for Forest Service Road : A Conceptual Study(Council for Advanced Transportation Studies, 1974-07) McGarragh, Thomas G.; Hudson, W. RonaldThe design of pavements for low-cost, low-volume roads is a complex procedure involving numerous variables. Because of the development of new information in the pavement field during the past decade, the complexity of the interaction of these design variables has become better understood and the need for a systematic approach to the problem of pavement design and management has become evident. This report is an attempt to apply this systematic approach to the design and management of low-volume Forest Service roads. The report summarizes the problem analysis efforts of the project staff, beginning with the identification of the problem through its recognition and definition. Using the FPS type of working Pavement Design System developed in Texas as a conceptual base, an extensive examination of the major subsystems that make up the majority of existing pavement management systems for "higher type" roads was conducted. In attempting to define these basic components for the proposed low-volume road system, it was found that interaction between the project research staff and Forest Service personnel was of great importance. This interaction was achieved in the form of an interagency "brainstorming session" and later an "importance rating" of the ideas presented at this meeting. The results of this interaction along with the research efforts of the project staff allowed for an initial definition of the major components in the proposed system. Where complete definition of these subsystems was not possible, relevant questions and ideas were formulated for consideration in their further development. Finally, an example conceptual pavement management system for low-volume roads that incorporates all the ideas and concepts developed during the past year's research is presented. It is concluded that the development of pavement management systems for low-volume Forest Service roads is indeed feasible and should be pursued in Phase II of the project. Recommendations for major areas of further research are also given.