New flood records are being set across the world as precipitation patterns change due to a warming climate. Despite the presence of longstanding water management infrastructure like levees and reservoirs, this rise in flooding has been met with property damage, loss of life, and hundreds of billions in economic impact, suggesting the need for new solutions. In this work, the authors suggest the active management of distributed networks of ponds, wetlands and retention basins that already exist across watersheds for the mitigation of flood damages. As an example of this approach, we investigate optimal control of the gated outlets of 130 such locations within a small watershed using linear programming, genetic algorithms, and particle swarm optimization, with the objective of reducing downstream flow and maximizing basin storage. When compared with passive operation (i.e., no gated outlets) and a uniformly applied active management scheme designed to store water during heavy rainfall, the optimal control techniques (1) reduce the magnitudes of peak flow events by up to 10%, (2) reduce the duration of flood crests for up to several days, and (3) preserve additional storage across the watershed for future rainfall events when compared with active management. Combined, these findings provide both a better understanding of dynamically controlled distributed storage as a flood fighting technique and a springboard for future work aimed at its use for reducing flood impacts.

The state of Iowa in the Central United States has experienced increasing flooding, with major events occurring most recently in 1993, 2008, 2011, and 2019. These floods caused over $23B in damage despite Iowa's three flood control reservoirs and expansive levee systems, suggesting the need for additional solutions. Iowa is home to over 4,000 small dams whose cumulative capacity more than double the state's current flood storage. These locations are operated passively, i.e., without the use of gated outlets to control basin storage utilization, thus limiting their flood mitigating potential. Here, the authors simulate gated outlets at 130 small dams within a 660 km2 watershed to (1) evaluate how effectively these storages can be activated across a watershed using gated outlets; and (2) quantify the utilization capacity of an activated distributed storage system for flow reduction. The authors used stochastic storm transposition to generate thousands of spatially variable rainfall events using Stage IV rainfall data within the Iowa domain at durations of 6, 12, 24, and 48 h and annual exceedance probabilities (AEPs) of 0.2, 0.1, 0.02, and 0.01. This expands the effective period of record, providing storms of various durations, intensities, and spatiotemporal distributions. An active management scheme was defined within the reservoir module of the hillslope link model designed to store water within the ponding locations. The study calculated the flow reductions that were achieved through this active scheme and found that flows were reduced for every rainfall duration and probability regardless of basin spatial scale. Reductions reached as high as 70% for a 6 h, 0.2 AEP event at a 93 km2 drainage area, while flows were reduced by roughly 12% for a 48 h, 0.01 AEP event at the basin outlet. This work establishes activated distributed storage as a meaningful flood reduction measure under realistic rainfall conditions at a variety of spatial scales.