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（floodplain）承担着多项关键生态功能。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处泛滥平原保护地管理者的调研显示，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、发生频率、持续时长与时机的各类指标。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河段，对现有一维HEC-RAS水力模型进行插值处理：该模型以间距小于1公里的河道断面为计算基础，以每日为时间步长，基于80年的水文观测序列，充分刻画了密苏里河与密西西比河汇口上游约800公里河段的水面剖面形态。为将模拟得到的水面高程转换为淹没水深，我们采用了融合泛滥平原激光雷达（LIDAR）与河道水深测量数据的地形模型，通过将模拟水面高程减去该地形模型的高程值，即可得到淹没水深。我们针对密苏里河从内布拉斯加州鲁洛至其与密西西比河汇口的800公里河段完成了上述计算，该方法最终生成了空间分辨率为30米的网格单元对应的29000余天的泛滥平原淹没水深时间序列。本数据集涵盖两种情景下的17项指标：其一采用HEC-RAS模拟得到的基准水位时间序列，其二则采用经调整的水位时间序列，以适配某一潜在气候变化情景下的流量变化。上述指标均以逐像素方式计算，涵盖了泛滥平原管理者关注的、与目标动植物相关的各类时间维度标准，例如生长季内的年均淹没天数。此外，本数据集还提供了两种情景下按重现期划分的泛滥平原水深分布图，以及每个像素首次被淹没的最小重现期。最后，本数据集还附带了我们用于基于插值水面高程计算淹没水深的基础高程图层。