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，河漫滩（floodplain）承担着诸多重要的生态功能。近期一项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80名河漫滩保护地管理者的调研显示，优化河漫滩管理所需的核心信息，集中于表征淹没（inundation）深度、范围、频次、持续时长与发生时机的各类指标。此类指标可通过基于云端的交互式地图高效传递给管理者。为计算此类指标，我们针对密苏里河下游对现有一维HEC-RAS水力学模型进行了插值处理：该模型基于80年的逐日实测数据序列，在密西西比河汇流点上游约800公里的河段上，对间距小于1公里的断面处的水面高程进行模拟，以充分表征该河段的水面剖面。为将水面高程转换为淹没水深，我们通过减去融合了河漫滩激光雷达（LIDAR）与河道测深（bathymetric）测量数据的合并地形模型，完成了这一转换。我们在内布拉斯加州鲁洛至密苏里河与密西西比河汇流点的800公里密苏里河河段上完成了上述计算。该方法生成了空间分辨率为30米的网格单元对应的河漫滩淹没水深时间序列，时长超29000天。本数据集包含两种情景下的共17项指标：其一为基于HEC-RAS模拟得到的基准水位过程时间序列，其二为针对某一潜在气候变化情景下径流量（discharge）变化进行校正后的水位过程时间序列。此类指标以单个像素为单元进行计算，涵盖了河漫滩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。本数据集还包含两种情景下基于重现期（return interval）的河漫滩水深分布图，以及每个像素发生淹没的最小重现期。最后，本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准高程图层。