Green stormwater infrastructure: function balancing of rain gardens, laboratory testing of outlet rating curves and precise delineation of small catchment areas
Creators: name: Zhou, Zikai
Publisher: name: No Publisher Supplied
Year: 2021

description: Increased impervious surfaces associated with urban development, can lead to increased flood risk. Green infrastructure (GI) is system of distributed water management which could protect, restore, and improve ecosystem by mimicking the natural hydrologic cycle, unlike traditional gray infrastructure which is designed to convey stormwater to a downstream discharge. GI takes advantage of natural processes such as infiltration to manage runoff. Rain gardens are an example of a stormwater management best management practice (BMP) designed to catch and infiltrate runoff to reduce the stormwater load to the sewers. The objective of this dissertation research was to investigate design parameters for optimization of rain garden performance. Design parameters that were investigated include: 1) Alternative drainage designs for rain gardens built on soil of low permeability and evaluate hydrological performances on annual basis as well as for individual design storms; 2) Water stage-flow rate relationships (rating curves) for the outlet structure with scour-protection gravel pile commonly used in GI measures, and 3) Watershed boundaries precisely delineated from high-resolution digital elevation model (DEM) generated from emerging static LiDAR technology.Typically rain gardens require a minimum permeability to facilitate infiltration. It is recommended to not build them on a base soil with low permeability due to the limited capacity of water infiltration and the long water ponding time. An investigation was completed to investigate the performance of rain gardens installed in a low permeability area with and without drainage. A numerical model was created to assess hydrological performances of the rain garden based on three different drainage designs, including no-drain, surface-drain and underdrain designs. The surface drain system has the best overall hydrologic performance among the three drainage designs and would be a good addition to rain gardens installed on subsoils of low permeability. The depth and duration that a rain garden holds water is often dependent upon the design of an outlet structure, especially in areas with limited infiltration. Laboratory testing was conducted to measure rates of flow discharge through the combined outlet structure (orifice-weir) with a gravel pile in the front at different water stages. Energy loss is less when applying the gravel pile to broad crested weir. Flow rate of combined outlet structure with gravel could not be simply calculated by adding orifice and weir flow equations together. Finally, GI is typically used for stormwater management in small catchments. It is rarely precise enough to use a relatively low-resolution DEM from traditional land surveying or airborne LiDAR to delineate a small flat watershed. A methodology of delineation of watershed for the porous parking lot using the static LiDAR point cloud and ArcGIS tool has been developed and validated with the field observed flow paths and boundaries. This research also evaluated accuracy of the delineated drainage area from using different resolutions of DEM generated by static LiDAR and airborne LiDAR. The results indicate that a finer resolution of DEM from terrestrial laser scanning (TLS) is more successful at realistically delineating small mild-sloped catchment areas which will improve hydrological design and modeling. A primary contribution of this dissertation research is development of a modeling framework that could be employed to optimize the hydrological performance of rain gardens with alternative drainage designs. The parameters discussed including drainage for low permeability soils, outlet configuration, and high-resolution watershed delineation represent progress in the development of rain garden design for stormwater management.