Science to Inform Management of Floodplain Conservation Lands under Non-Stationary Conditions

Within large-river ecosystems, floodplains serve a variety of important ecological functions. A recent survey of 80 managers of floodplain conservation lands along the Upper and Middle Mississippi and Lower Missouri Rivers in the central United States found that the most critical information needed to improve floodplain management centered on metrics for characterizing depth, extent, frequency, duration, and timing of inundation. These metrics can be delivered to managers efficiently through cloud-based interactive maps. To calculate these metrics, we interpolated an existing one-dimensional HEC-RAS hydraulic model for the Lower Missouri River, which simulated water surface elevations at cross sections spaced (<1 kilometer) to sufficiently characterize water surface profiles along an approximately 800 kilometer stretch upstream from the confluence with the Mississippi River over an 80-year record at a daily time step. To translate these water surface elevations to inundation depths, we subtracted a merged terrain model consisting of floodplain LIDAR and bathymetric surveys of the river channel. We completed these calculations for an 800 kilometer stretch of the Missouri River, spanning from Rulo, Nebraska to the river's confluence with the Mississippi River. This approach resulted in a 29,000+ day time series of inundation depths across the floodplain using grid cells with 30 meter spatial resolution. This dataset presents 17 metrics for each of two scenarios, one using a baseline timeseries of stages from the HEC-RAS simulation and one using a timeseries of stages adjusted to account for changes in discharge under one possible climate change scenario. These metrics are calculated on a per pixel basis and encompass a variety of temporal criteria generally relevant to flora and fauna of interest to floodplain managers, including, for example, the average number of days inundated per year within a growing season. We also include a series of maps of water depths across the floodplain by return interval for each scenario, and the minimum return interval at which each pixel is inundated. Lastly, we include the base elevation layer that we generated to calculate depth of inundation from interpolated water-surface elevations.

在大型河流生态系统中，洪泛平原承担着多种重要的生态功能。针对美国中部密西西比河上游、中游以及密苏里河下游沿岸的80名洪泛平原保护土地管理者开展的近期调研显示，优化洪泛平原管理所需的核心信息，集中于表征洪水淹没深度、范围、频次、持续时长与发生时机的各类指标。上述指标可通过基于云端的交互式地图高效交付给管理者。为计算上述指标，我们针对密苏里河下游的现有一维HEC-RAS水力学模型进行插值处理。该模型以日时间步长，基于80年的逐日水文记录，对密西西比河汇流点上游约800公里河段的断面（间距小于1公里）处的水面高程进行模拟，从而充分刻画该河段的水面形态。为将水面高程转换为淹没水深，我们将合并后的地形模型（由洪泛平原激光雷达（LIDAR）与河道水深测量数据构建）与水面高程做差值运算。本次计算覆盖了密苏里河从内布拉斯加州鲁洛（Rulo）至其与密西西比河汇流点的800公里河段。本方法生成了空间分辨率为30米的网格单元对应的洪泛平原淹没水深时序数据，时长超29000天。本数据集包含两种情景下的17项指标：其一为基于HEC-RAS模拟的基准水位时序数据，其二为针对某一气候变化情景下的径流变化进行校正后的水位时序数据。上述指标以单个像素为单位计算，涵盖了洪泛平原管理者关注的各类与动植物相关的时间维度标准，例如生长季内年均淹没天数。本数据集还提供了两种情景下基于重现期的洪泛平原水深分布图，以及每个像素首次被淹没的最小重现期。此外，数据集还包含我们为通过插值水面高程计算淹没水深所生成的基础高程图层。