Impact of Inland Bathymetry on Applications. Flood inundation, channel hydraulic geometry and flood flow estimates

Presentation given at TopoBathy Workshop Sept 17-18, 2019, Tuscaloosa, Alabama.

Flood inundation is difficult to map, model, and forecast because of the data needed and the computational demand. Recently an approach based on the relative elevation, or Height Above Nearest Drainage (HAND), which is derived from a digital elevation model (DEM), has been suggested for both flood mapping and obtaining reach hydraulic properties and synthetic rating curves. These products are only as good as the underlying DEM from which they are derived and thus better inland bathymetry offers the potential for incorporating bathymetry into national scale models to improve flood inundation modeling and mapping. This presentation will review the approach for using relative elevation in flood modeling, describing how HAND is calculated, how it is used to map flood inundation for stream reach catchments and how it is used to determine stream reach properties, identifying shortcomings and giving ideas for improvements. As we obtain more detailed information on bathymetry, topography and hydrography it is important to establish a consistent data model for the river bed that is used in HAND related work that aligns and reconciles elevation and hydrography. This presentation will discuss approaches for using hydrography to remove DEM obstacles, the segmentation of streams used in deriving HAND reach average hydraulic properties and ideas for quantifying reach average roughness based on HAND and flood inundation mapped from remote sensing of previous floods with measured discharges.

本汇报于2019年9月17日至18日在阿拉巴马州塔斯卡卢萨举办的TopoBathy研讨会上发表。

洪水淹没范围的制图、建模与预报历来颇具挑战，这源于其所需的数据量与计算资源需求均较高。近年来，基于相对高程的方法——即由数字高程模型（Digital Elevation Model, DEM）衍生而来的近邻河道高程（Height Above Nearest Drainage, HAND）——被提出并应用于洪水淹没制图、河道水力参数获取以及合成水位流量关系曲线构建等场景。此类衍生产品的精度严格依赖于其基础DEM的质量，因此更精准的内陆水深地形数据有望将水深信息纳入国家级尺度模型，进而提升洪水淹没模拟与制图的精度。本次汇报将梳理基于相对高程的洪水建模方法，详细阐释HAND的计算逻辑、其在河道汇水区洪水淹没范围制图中的应用方式，以及其在河道水力参数测定中的应用场景，同时指出该方法现存的不足并提出改进思路。随着我们获取到更为精细的水深地形、陆地地形与水文测绘数据，建立一套适用于HAND相关研究的河床统一数据模型以协调统一高程与水文测绘信息，已成为一项关键工作。本次汇报还将探讨利用水文测绘数据消除DEM数据缺陷的方法、用于推导HAND河道平均水力参数的河道分段方案，以及基于HAND与结合实测流量的历史洪水遥感反演得到的淹没范围数据量化河道平均糙率的相关思路。