Identification and Analysis of Microscale Hydrologic Impacts and Hazards Using Unmanned Aerial Systems

As computational resources and observational capabilities improve in the physical and earth sciences, there is a general push (and expectation) of more accurate and detailed predictions based on numerical models. While accuracy is inherently based on the physical and/or statistical strength of the model, the amount and quality of data used to define initial and boundary conditions is critical. This relates back to model detail in that higher spatial and temporal model resolution requires an equal (if not greater) increase in the volume and frequency of data needed for viable output. Unfortunately, as models tend toward higher spatial resolution there is not a corresponding increase in observations to initialize or verify simulations; therefore, the potential benefit of the improved modeling framework is not always realized. Such an approach is particularly true in terms of hydrologic models due to the direct relationship between fine-scale surface features and water flow along a particular river section. Although the dynamics of water movement through a channel are well known, the particular characteristics of the channel both before and during a high-water event may not be characterized at the level of the model, leading to the need for assumptions that detract from the overall value of the simulations. Based on this need, new and/or updated approaches in observations of river systems are needed that are in-line with the current push towards microscale model simulations. One method that is gaining popularity across a range of disciplines is the use of data from unmanned aerial systems (UAS), which are unmanned aerial vehicles (UAV) with dedicated imaging, sensor, and communication packages related to a specific mission or application. In the case of this project, a fixed-wing UAV (Griffon Outlaw G2E, 180 lb. take-off weight) with visible (red-green-blue; RGB), near-infrared (NIR), and longwave infrared (LWIR) cameras (Overwatch Imaging TK-5) was used to overfly areas near Greenwood, MS before and during a flood event in February 2019 with the purpose of providing high-resolution imagery (4500’ AGL flight altitude provides ~6” GSD for RGB/NIR imagery and ~24” imagery for LWIR) for analysis of hydrologic and hydraulic features. The pre-event flight was conducted on January 16, 2019 while flights on February 24-25, 2019 coincided with rising floods along the Tallahatchie, Yalobusha, and Yazoo Rivers near Greenwood. The imagery obtained from these missions provide direct examples of fine-scale surface features that can alter water level and discharge, such as engineering structures (i.e., levees and bridges), natural storage features (low-lying agricultural fields), and areas of natural resistance (inundated forests). While the influence of these features may be recognized within the physical construct of a numerical model, their existence and specific behavior on a larger scale may not be; therefore, the aim of this project is to define and illustrate the hydrologic response of river flooding relative to microscale surface properties to enhance the scientific understanding of how large-scale flooding influences and is influenced by such features. This type of information is critical in defining where and how to incorporate high-resolution information into hydrologic models, and also provides an invaluable dataset for eventual verification of hydrologic simulations through inundation mapping. Additionally, this project will highlight the advantages and requirements for the use of UAS platforms in hydrology in terms of both operations and research applications.