Canyonlands Field Drainage Report
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CANYONLANDS FIELD Moab, Utah DRAINAGE REPORT Hangar Area Drainage Analysis ACI No. 176422 July 2017 861 Rood Ave. Grand Junction, CO 81501 O: 970-242-0101 F: 970-241-1796 www.armstrongconsultants.com TABLE OF CONTENTS 1.0 SCOPE OF WORK ................................................................................................................. 1-1 1.1 Narrative .................................................................................................................... 1-1 2.0 PHOTOGRAPHS ................................................................................................................... 2-1 3.0 DRAINAGE ........................................................................................................................... 3-1 3.1 Rainfall, Runoff, Storm Drain Design ......................................................................... 3-1 3.2 Existing Conditions ..................................................................................................... 3-1 3.3 Proposed Storm Drainage System for Existing Conditions ........................................ 3-1 3.4 Drainage for Future Development ............................................................................. 3-2 3.5 Development Sequence ............................................................................................. 3-2 4.0 OPINION OF COST ............................................................................................................... 4-1 4.1 Estimate of Probable Construction Cost .................................................................... 4-1 LIST OF APPENDICES Appendix 1 Proposed Storm Drain System Plan Appendix 2 Drainage Calculations Hangar Area Drainage Analysis TOC-1 176422 Canyonlands Field INTRODUCTION The firm of Armstrong Consultants, Inc. was retained by Grand County to provide the necessary studies and engineering analysis of the conditions located at the airport. The engineering rationale used for this drainage analysis, is presented in this report. 1.0 SCOPE OF WORK 1.1 Narrative Canyonlands Field Airport has received numerous requests for hangar space and needs to develop areas to facilitate hangar development and extend taxilanes for access. In order to facilitate development and mitigate storm water impacts with the current hangar facilities and future hangar development, a study was required to evaluate the existing and anticipated drainage requirements in the hangar area. A conceptual grading and drainage system plan was developed as part of the study to address the existing drainage concerns in the vicinity of the identified hangar development area. A conceptual grading and layout plan was developed for future apron development as depicted on the 2015 Airport Layout Plan (ALP). The drainage study evaluated the drainage patterns on the airfield and makes recommendations for improving the existing conditions, as well as storm water management recommendations for future development based up on the development as depicted on the ALP. The soils at Canyonlands Field are composed of surficial deposits that can exhibit moderate to very high swell potentials. Swell potentials vary with moisture content, density, and the clay chemistry and mineralogy, and can vary markedly both laterally and vertically. The shale weathers easily when exposed and forms soft highly erodible slopes and hills that also have the potential to be collapsible. Because of the nature of the soils found at the site, it is critical that the developed areas be drained effectively to minimize the fluctuations in moisture content and also minimize erosion. Hangar Area Drainage Analysis 1-1 166393 Canyonlands Field THIS PAGE WAS INTENTIONALLY LEFT BLANK 2.0 PHOTOGRAPHS NORTH SIDE EXISTING APRON AREA LOOKING SOUTH MIDDLE OF EXISTING APRON AREA LOOKING SOUTH Engineer’s Design Report 2-1 166393 Canyonlands Field MIDDLE OF EXISTING APRON AREA LOOKING SOUTHWEST LOOKING SOUTH TOWARD FUTURE DEVELOPEMENT AREA Engineer’s Design Report 2-2 166393 Canyonlands Field LOOKING NORTH FROM FUTURE DEVELOPEMENT AREA Engineer’s Design Report 2-3 166393 Canyonlands Field THIS PAGE WAS INTENTIONALLY LEFT BLANK 3.0 DRAINAGE 3.1 Rainfall, Runoff, Storm Drain Design Hangar and pavement development affect the area runoff due to the significant increase in impervious area and the tendency to concentrate storm water flowing off and around structures and pavement. The intent of the storm drainage system is to capture and direct the storm water off of the ramp and hangar area while minimizing pooling, erosion, or flooding in any areas in the vicinity. 3.2 Existing Conditions Currently, there are not any major storm water drainage structures in the hangar and taxilane areas. The storm water currently drains across the surface of the taxilanes and through the hangar areas from east to west. During significant rainfall events, sediment is carried by the storm water onto the pavement. The presence of hangars causes the storm water to run off of the roofs and flow in concentrated streams along the sides and between the buildings, encouraging erosion. Also, there are undeveloped low-lying areas that allow storm water to pool and remain until it absorbs into the soil or evaporates. The soil may become saturated in these areas causing the soil to swell, increasing the pressure and upward force on the foundations of the hangars. As the water in the soil dissipates or dries, the amount of swell reduces as the moisture content reduces. This fluctuation in the soil moisture content can cause movement and settling of the hangars and pavement that can lead to premature failure of the building foundation or pavement. 3.3 Proposed Storm Drainage System for Existing Conditions In order to minimize the current issues, it is recommended that a storm water runoff system is established which allows the storm water to drain in a controlled manner off of the apron and hangar area with minimal erosion or ponding. For the existing hangar area a combination of a concrete swale and a storm pipe network with inlets allows for minimal disturbance to existing underground utilities while controlling the storm water flow and reducing erosion. In areas where significant amounts of underground utilities are located, a concrete swale is proposed to capture surface flows and direct it into the underground storm drains. The concrete swale directs the storm water into an inlet connected to a series of storm pipes which would carry the storm water underground and release it to the west of the apron and hangar area. A series of inlets are connected to the storm pipe network to capture other area storm water flows. An Engineer’s Design Report 3-1 166393 Canyonlands Field opinion of cost for the proposed drainage system can be found in the Section 4 of this report. See the drainage plan in Appendix A for the proposed storm drain layout for the existing conditions. In addition to the proposed storm drain system, it may be beneficial to cover the existing soil with gravel. This would require minimal grading and would not have a significant impact on the existing underground utilities and would help reduce the amount of surface erosion that takes place during significant rainfall events. 3.4 Drainage for Future Development According to the current Airport Layout Plan, future hangar development is expected to take place to the south of the existing hangar area. The taxilanes will be extended with hangars developed alongside in a similar arrangement as the existing hangar and taxilane configuration. The proposed network of storm drains was developed to accommodate future pavement and hangar development. The storm drain system was designed with the intention of allowing the system to be constructed in segments as the hangars are developed. As each hangar is developed, the subsequent section of storm drains and inlets would be developed. Each newly constructed section would connect to the previously constructed storm drain network. The primary trunk of the storm drain would be located in a designated utility easement area defined prior to hangar and taxilane development. This would allow for the establishment a drainage pattern and controlled elevations for future development. The proposed location of the utility easement is included in the attached drawings in Appendix A. In order to effectively establish a drainage plan that can be constructed in segments, elevations and grades need to be established for the flowlines of the pipe, the inlets, the approximate hangar floor elevations, and the elevations of the future pavement. Proposed elevations are included in the drainage plan in Appendix A. An opinion of cost for this storm drain network can be found in Section 4 of this report. 3.5 Development Sequence The elevations and layout of the future development were determined in order to allow for the orderly development of the future hangar area. Because the hangar development area is on a sloping hill side, it is critical that the positioning of the pavement, hangars, and drainage system are all accounted for and Engineer’s Design Report 3-2 166393 Canyonlands Field determined prior to development. If the development is constructed according to the proposed elevations, the drainage patterns established for the drain system and pavement runoff will be functional and reduce the instances of flooding, erosion, or ponding due to hangar development. Elevations shown on the attached drawings should be used as a general guide for the development. Although hangar development may not occur