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，泛滥平原（floodplains）具备多种关键生态功能。近期一项针对美国中部密西西比河上中游及密苏里河下游沿岸80处泛滥平原保护地管理者的调研结果表明，优化泛滥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平台的交互式地图高效推送至管理者。为计算上述指标，我们针对密苏里河下游河段，对现有一维HEC-RAS水力学模型进行了插值处理：该模型以间隔小于1千米的断面模拟水面高程，足以在日时间步长的80年水文序列中，完整刻画密苏里河与密西西比河汇流点上游约800千米河段的水面形态。为将水面高程转换为淹没水深，我们基于合并后的地形模型开展计算，该模型整合了泛滥平原激光雷达（LIDAR）与河道水深测量数据。我们针对从内布拉斯加州鲁洛至密苏里河与密西西比河汇流点的800千米密苏里河河段完成了上述计算，最终生成了空间分辨率为30米的网格单元对应的逾29000天的漫滩淹没水深时间序列。本数据集包含两种情景下的17项指标：其一为基于HEC-RAS模拟水位序列的基准情景，其二为针对某一可能气候变化情景下径流变化进行调整后的水位序列情景。所有指标均逐像素计算，涵盖了泛滥平原管理者关注的动植物相关的各类时间维度标准，例如生长季内年均淹没天数。我们还提供了两种情景下基于重现期的漫滩水深分布图，以及每个像素首次被淹没的最小重现期。最后，本数据集包含我们为从插值水面高程计算淹没水深而生成的基础高程图层。