Approach
Overland flows occur when soils cannot absorb water, such as when rain or meltwater flows over saturated soils, or as a result of rain intensity that is too high for vegetation and soils to absorb. Even modest changes in precipitation can amplify the magnitude and volume of overland flows and cause rapid changes in surface water levels following rain events. The initiation acceleration of water movement is largely controlled by the intensity of rainfall or snowmelt combined with site characteristics such as slope, vegetation density, soils, antecedent moisture condition, and land-use. Higher water velocity increases risk of soil erosion, particularly on wet or steep slopes, which can degrade water quality and aquatic habitat. A suite of best management practices for reducing overland flow may include actions to increase surface roughness and canopy interception, maintain soil porosity, and otherwise disperse concentrated or fast-moving flows of water. Planning to anticipate and reduce overland flow sources is particularly important in areas prone to erosion, adjacent to infrastructure, and subject to early and rapid snowmelt over frozen soils.
Tactics
- Strategically place downed wood to deflect, slow and pool overland flow water as snow melts over saturated soils and frozen soils.
- Use wattles and water bars to slow overland flow water velocity and increase retention and recharge into soils.
- Increase roughness characteristics on slopes receiving overland flows by planting woody vegetation rather than grasses to quickly reduce water velocity and sedimentation.
- Plan development of impervious areas (such as roads, trails, skid trails, campgrounds, parking lots) away from surface waters to minimize initiation of direct flow paths and rill and gully formation. If no longer needed disk compacted surface, resurface.
- Promptly revegetate exposed soils and establish vegetation tolerant of increased soil saturation, submergence and force from high velocity flows such as species with shorter-stature, submergence and force from high velocity flows such as species with shorter-stature, with well-developed deep and wide root systems, and species able to quickly
- Redesign road infrastructure to divert overland flows into forests or woody vegetation and away from surface waters. Vegetate fill slopes with a mix of species, favoring woody vegetation to slow overland flows.
Strategy
Strategy Text
This strategy aims to help ecosystems adjust in response to fundamental changes in hydrologic processes altered by a changing climate. The timing, form, and spatial distribution of precipitation is changing with the climate, with cascading effects on forest hydrologic cycles that affect water yield and water quality. Forest species assemblage, structure, and habitat quality will shift with changes in the nature and timing of water availability. Anticipating potential impacts to water levels and quality in management planning may help managers reduce risks and take advantage of opportunities to sustain hydrologic function. Broadly considering climate related alterations to the hydrologic cycle along with site-level responses and potential land-use changes is likely to provide the most complete picture of risks and opportunities.
Shannon, P.D.; Swanston, C.W.; Janowiak, M.K.; Handler, S.D.; Schmitt, K.M.; Brandt, L.A.; Butler-Leopold, P.R.; Ontl, T.A. (in review). Adaptation Strategies and Approaches for Forested Watersheds. Ecological Applications.