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，漫滩（floodplain）承担着诸多关键生态功能。近期一项针对美国中部密西西比河上中游与密苏里河下游沿岸80处漫滩保护地管理者的调研显示，优化漫滩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量化指标。上述指标可通过基于云端的交互式地图高效传递给管理者。为计算上述指标，我们针对密苏里河下游，对现有一维HEC-RAS水力模型开展插值处理，以模拟河道水面高程：该模型以间距小于1公里的河道断面为基础，可基于80年的日时间步长水文序列，充分表征密苏里河与密西西比河汇流点上游约800公里河段的水面剖面形态。为将水面高程转换为淹没深度，我们采用融合漫滩激光雷达（LIDAR）与河道水深测量数据的复合地形模型，通过水面高程减去该地形高程的方式完成计算。本次计算覆盖密苏里河从内布拉斯加州鲁洛（Rulo）至其与密西西比河汇流处的800公里河段。该方法生成了空间分辨率为30米的漫滩网格单元的29000余日淹没深度时间序列。本数据集包含两种情景下的17项指标：其一为基于HEC-RAS模拟得到的基准水位时间序列，其二为针对某一气候变化情景下径流量变化进行校正后的水位时间序列。上述指标均以单个像素为单元计算，涵盖了漫滩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。本数据集还包含两种情景下基于不同洪水重现期的漫滩水深分布图，以及每个像素被淹没的最小洪水重现期。此外，本数据集还包含我们为基于插值水面高程计算淹没深度所生成的基础高程图层。