Growth in urban populations creates opportunities for urban forests to deliver ecosystem services critical to human wellbeing and biodiversity. Our challenge is to strategically expand urban forests and provide our international communities, particularly the vulnerable, with healthier, happier, and enriched lives.

A semidistributed, physical‐based Urban Forest Effects – Hydrology (UFORE‐Hydro) model was created to simulate and study tree effects on urban hydrology and guide management of urban runoff at the catchment scale. The model simulates hydrological processes of precipitation, interception, evaporation, infiltration, and runoff using data inputs of weather, elevation, and land cover along with nine channel, soil, and vegetation parameters. Weather data are pre‐processed by UFORE using Penman‐Monteith equations to provide potential evaporation terms for open water and vegetation. Canopy interception algorithms modified established routines to better account for variable density urban trees, short vegetation, and seasonal growth phenology. Actual evaporation algorithms allocate potential energy between leaf surface storage and transpiration from soil storage. Infiltration algorithms use a variable rain rate Green‐Ampt formulation and handle both infiltration excess and saturation excess ponding and runoff. Stream discharge is the sum of surface runoff and TOPMODEL‐based subsurface flow equations. Automated calibration routines that use observed discharge has been coupled to the model. Once calibrated, the model can examine how alternative tree management schemes impact urban runoff. UFORE‐Hydro model testing in the urban Dead Run catchment of Baltimore, Maryland, illustrated how trees significantly reduce runoff for low intensity and short duration precipitation events.

Abstract:In-channel rock vane structures are widely used in stream restoration as a way to reduce stream channel erosion and create pool or riffle features. When these structures change hydraulic gradients they may affect ecological stream functions, such as hyporheic exchange flow (HEF) patterns. A study of constructed in-channel structure controls on HEF was conducted in the third-order Batavia Kill, New York using stream and hyporheic temperature amplitude analysis and computational fluid dynamics (CFD) hydraulic simulations. Temperature monitors were installed in the water column and channel bed at six locations around each of seven in-channel restoration structures (three cross-vanes and four J-hooks) at baseflow in 2007. Elevation surveys of the structures were then used to simulate HEF using CFD. The results indicate a pattern of pronounced upwelling in the run section just below the structure, upwelling transitioning to downwelling within the pool, and pronounced downwelling in the glide out of the pool. This pattern is consistent with natural riffle pool sequences. The direction of HEF inferred from the temperature amplitude analysis agreed with the direction of flow simulated with CFD at 80% of the locations, and the few disagreements were expected due to model limitations. CFD simulation demonstrated that increasing stream flows result in changes in HEF spatial patterns and magnitude at each structure. This work illustrates how CFD simulations can guide design of in-channel restoration structures for HEF function.

The conceptual model of hyporheic exchange below river steps may oversimplify exchange flow paths if it depicts a uniform pattern of downstream‐directed upwelling. This research used nonmobile, porous bed flume experiments and hydrodynamic simulation (CFD) to characterize hyporheic flow paths below a river step with a hydraulic jump. Bed slope was 1%, step height was 4 cm, downstream flow depth was 4 cm, substrate was 1 cm median diameter gravel, and hydraulic jump length was 25 cm in the flume and CFD experiments. With the hydraulic jump, flow paths changed to include downwelling beneath the water plunging into the pool and upstream‐directed upwelling at the base of the step and beneath the length of jump. Failure to represent the influence of static and dynamic pressures associated with hydraulic jumps leads to erroneous prediction of subsurface flow paths in 75% of the streambed beneath the jump. A refined conceptual model for hyporheic flow paths below a step with a hydraulic jump includes reversed hyporheic circulation cells, in which downwelling water moves upstream and then upwells, and flow reversals, in which the larger flow net of downstream‐directed upwelling encounters a nested flow path of upstream‐directed upwelling. Heterogeneity in hyporheic flow paths at hydraulic jumps has the potential to explain field‐observed mosaics in streambed redox patterns and expand structure‐function relationships used in river management and restoration.

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1Urban trees can help mitigate some of the environmental degradation linked to the rapid 2 urbanization of humanity. Many municipalities are implementing ambitious tree planting 3 programs to help remove air pollution, mitigate urban heat island effects, and provide other 4 ecosystem services and benefits but lack quantitative tools to explore priority planting locations 5 and potential tradeoffs between services. This work demonstrates a quantitative method for 6 exploring priority planting and ecosystem service tradeoffs in Baltimore, Maryland using 7 spatially explicit biophysical iTree models. Several planting schemes were created based on the 8 individual optimization of a number of metrics related to services and benefits of air pollution 9 and heat mitigation ecosystem services. The results demonstrate that different tree planting 10 schemes would be pursued based on the ecosystem service or benefit maximized, revealing 11 tradeoffs between services and priority planting locations. With further development including 12 consideration of additional ecosystem services, disservices, user input, and costs of tree planting 13 and maintenance, this approach could provide city planners, urban foresters, and members of the 14 public with a powerful tool to better manage urban forest systems.

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