Watersheds Chapter 9

Watershed All land enclosed by a continuous hydrologic drainage divide and lying upslope from a specified point on a stream All land enclosed by a continuous hydrologic drainage divide and lying upslope from a specified point on a stream Watershed = drainage basin = catchment Watershed = drainage basin = catchment

Watershed Management For the production and protection of water supplies and water-based resources For the production and protection of water supplies and water-based resources

Streamflow Two components: Two components: Total water yield - volume per time period Total water yield - volume per time period Flow regime - timing of yield Flow regime - timing of yield

Streamflow: Controlling Factors Climate : Climate : Temperature Temperature Precipitation Precipitation Evaporation Evaporation Humidity Humidity Solar radiation Solar radiation Wind Wind Freezing Freezing Atmospheric pressure Atmospheric pressure

Streamflow: Controlling Factors Topography: Topography: Basin size Basin size Shape Shape Slope Slope

Streamflow: Controlling Factors Geology: Geology: Type, volume of groundwater storage Type, volume of groundwater storage Material available for erosion, transport Material available for erosion, transport Rock chemistry (water chemistry) Rock chemistry (water chemistry)

Streamflow: Controlling Factors Vegetation: Vegetation: Controls volume, timing of water yield Controls volume, timing of water yield Controls sediment delivery Controls sediment delivery

Stream Hydrographs Different watersheds produce different stream hydrographs Different watersheds produce different stream hydrographs Discharge with respect to time Discharge with respect to time

Stream Hydrographs

Watersheds with poor water storage Watersheds with poor water storage Impermeable, shallow soils Impermeable, shallow soils Results in flashy response to snowmelt, precipitation Results in flashy response to snowmelt, precipitation

Stream Hydrographs

Watersheds with good water storage Watersheds with good water storage Deep, permeable soils Deep, permeable soils Little variation in hydrograph Little variation in hydrograph

Stream Hydrographs

Mountain watersheds Mountain watersheds Dominated by snowmelt runoff Dominated by snowmelt runoff Stable the remainder of the year Stable the remainder of the year

Stream Hydrographs

Sediment Output Sediment eroded from watershed Sediment eroded from watershed Major consideration Major consideration Produces 80% of water quality degradation Produces 80% of water quality degradation Interacts with other water quality components Interacts with other water quality components Directly affected by land use Directly affected by land use

Sediment Output

Surface erosion - overland flow Surface erosion - overland flow Sheet, rill, gully Sheet, rill, gully Mass movement - gravity, stress Mass movement - gravity, stress Contributes to suspended sediment load Contributes to suspended sediment load

Sediment Output Erosion/channel cutting Erosion/channel cutting Detachment, movement from stream channel by moving water Detachment, movement from stream channel by moving water Bedload Bedload

Sediment Output Stream power Stream power Sediment carrying capacity Sediment carrying capacity

Land-use Impacts Vegetation removal Vegetation removal Agriculture, development, forestry practices Agriculture, development, forestry practices Tend to increase water yield to streams Tend to increase water yield to streams

Agriculture Withdrawal for irrigation Withdrawal for irrigation Reduced stream power, reduced transport of sediments, vegetation encroachment, channel narrowing, reduced habitat quantity Reduced stream power, reduced transport of sediments, vegetation encroachment, channel narrowing, reduced habitat quantity

Agriculture Withdrawal for irrigation Withdrawal for irrigation May stabilize channel, stabilize baseflow by recharging shallow aquifers, prevent channel damage, improve stream habitat quality May stabilize channel, stabilize baseflow by recharging shallow aquifers, prevent channel damage, improve stream habitat quality

Agriculture Grazing Grazing Soil compaction, reduced vegetation, reduced infiltration, increased overland flow, flashy flows with reduced ability to maintain late season baseflows Soil compaction, reduced vegetation, reduced infiltration, increased overland flow, flashy flows with reduced ability to maintain late season baseflows

Urbanization Reduced infiltration, increased overland flow, increased peak flows, rapid runoff response, reduced water quality Reduced infiltration, increased overland flow, increased peak flows, rapid runoff response, reduced water quality

Watersheds vs. Fisheries Link between watershed characteristics and stream habitat quality (fish carrying capacity) Link between watershed characteristics and stream habitat quality (fish carrying capacity)

Watersheds vs. Fisheries 1) Prioritize streams for management based upon potential 1) Prioritize streams for management based upon potential

Watersheds vs. Fisheries 2) Estimate influence of land use types, intensities on fisheries 2) Estimate influence of land use types, intensities on fisheries

Watersheds vs. Fisheries 3) Integrate fisheries into existing land classification system 3) Integrate fisheries into existing land classification system

Riparian Zones Streamside areas Streamside areas Vegetation Vegetation Many important roles: Many important roles: 1 - bank stabilization 1 - bank stabilization 2 - slow floodwaters 2 - slow floodwaters 3 - promote infiltration, aquifer recharge 3 - promote infiltration, aquifer recharge Improve subsequent baseflow Improve subsequent baseflow

Riparian Zones 4 - trap sediment 4 - trap sediment Reduces sediment yield Reduces sediment yield 5 - reduce nutrient loading 5 - reduce nutrient loading 6 - control nonpoint- source pollution 6 - control nonpoint- source pollution 7 - contribute woody debris (fish cover) 7 - contribute woody debris (fish cover)