How do humans affect watersheds and the hydrologic
cycle?
Human caused disturbances
• Agriculture
• Timber harvest
• Mining
• Urbanization
• Introduction of exotic species
• Harvesting of fish and wildlife
Land use/cover and vegetation
Physiography Climate
Landscape controls
NutrientInputs
Solar energy and
Organic input Regime
Habitat FormingProcesses
Species assemblages
Stream Morphology andConditions
Biodiversity
Habitat characteristics & conditionse.g., pools, riffles, temperature, etc.
Sedimentand StreamflowRegime
Modified from Roni et al. 2002.
Land Use and Vegetation
• The landscape control factor on which humans have the most influence
– Mining: extent of vegetation alteration depends on type of mining
– Forestry: tree removal and replacement over time
– Urbanization: tree removal and replacement with grass and impervious surfaces
– Agriculture: tree removal and replacement with pasture or crops
Effects of vegetation removal on hydrology and streams
• Precipitation ?
Effects of vegetation removal on hydrology and streams
• Precipitation ?
• Evapotranspiration ?
Effects of vegetation removal on hydrology and streams
• Precipitation ?
• Evapotranspiration
• Infiltration ?
Effects of vegetation removal on hydrology and streams
• Precipitation ?
• Evapotranspiration
• Infiltration
• Surface runoff ? Subsurface runoff ?
Effects of vegetation removal on hydrology and streams
• Evapotranspiration
• Infiltration
• Surface runoff Subsurface runoff
• Frequency and magnitude of
peak flows ?
Effects of vegetation removal on hydrology and streams
• Evapotranspiration
• Infiltration
• Surface runoff Subsurface runoff
• Frequency, magnitude and timing of
peak flows
• Materials transported to stream ?
Effects of vegetation removal on hydrology and streams
• Evapotranspiration
• Infiltration
• Surface runoff Subsurface runoff
• Frequency and magnitude of
peak flows
• Materials transported to stream
Aggregate Mining
In-channel mining
In-channel and floodplain miningPhotos by M. Kondolf
Effects of instream aggregate mining
• Continuity of sediment transport interrupted
• Produces local sediment deficit
• Can lead to increase accumulation of fines and blocking of sediment
Effects of instream aggregate mining
• Incision can lower the water table
• This can lead to loss of groundwater storage
• Can affect hyporheic zone
• Reduce summer base flow
Effects of floodplain and terrace mining
• Pumping to dewater pits – can lower base flows in the channel and
increase evaporation from the waste pits – may increase saltwater intrusion near coasts
• If channel migration captures the pits, in-channel storage ponds will alter flow travel times
• Old pits may be altered to serve as off-channel winter habitat for salmon
FORESTRY
Photos by R.S. Lindsay
Photo by Carrie Inman
Agriculture
URBANIZATION
Forestry, agriculture and urbanization
All of these human activities alter the watershed
What alterations do they have in common?
Forestry, agriculture and urbanization
• Remove trees and other vegetation
• Soil compaction – increased runoff
• Reduce organic matter delivery
• Build roads
Large storage in soil, channel and valley floor Recharge
Natural cleaning
Pollutant wash off
No recharge
Rapid flow limited storage
Slow flow
Natural Developed
Reduced soil storageLimited infiltration
Precipitation
Floods and Urbanization
surface runoff vs. infiltrationnatural land cover vs. urban area
TREE REMOVAL
INTERCEPTION EVAPOTRANSPIRATION
SOIL MOISTURE
SATURATED SUBSURFACE/SURFACE FLOW
RATE OF TIME IT TAKES WATER TO TRAVELTO CHANNELS FROM STORM RUNOFF
CHANGES TO WOOD/ORGANIC REGIME
CHANNEL ROUGHNESS ANDSTORAGE
RATE OF WATER TRAVEL TIME THROUGH CHANNEL
FLOW PEAKS EARLIER AND HIGHER DOWNSTREAM
Drainage Density
time
Q
time
Q
Low peak, gradual riseand fall
Higher peak, quicker rise and fall
Roads,Ditches,Drains
Channels
P P
Lower drainage density
Higher drainage density
Roads and Soil Modification
CompactedSoil
Soil removal/Cut banks
Ditches, culverts, drains
InfiltrationSoil water
Storage space
Surface runoff
Subsurface flowinterception
Drainage density and water delivery to streams
Soil saturation
How do we manage watersheds?
• Dept of Natural Resources Regulations
• U.S. Forest Service Regulations
• Clean water act
• Endangered Species Act
• Total Maximum Daily Loads (TMDLs)
• City and County Regulations
Washington Water Types
• Type S – Shorelines and large rivers
• Type F– Rivers and associated wetlands, lakes, ponds, etc. >
0.5 acres at seasonal low level and have FISH
• Type Np– Perennial streams without fish
• Type Ns– All other streams not included above- seasonally dry
streams without fish
Regulations a function of water type and forest site class
Core: No harvest or construction except for permitted road activitiesInner Zone: Harvest allowed but must meet future desired conditions standards (140 yrs)Outer Zone: Must leave 20 conifer trees per acre > 12 inched dbh
Lab reminders
• Remember Q (discharge) = Area X velocity – Q units are volume/time – Area units are ft or meters squared– Velocity units are ft or m per second
Lab reminders
• Velocity meter method:– Do NOT take the average velocity of your flow meter
measurements and multiply by cross-sectional area to get discharge Q. The velocity meter method involves summing the delta Qs to get the total Q.
– That is, as your diagrams indicate, each place you took a velocity measurement is the center of a small area of the stream cross-section. As with the float method, Q=VA. As the spreadsheet indicates, compute Q for each small area and then sum all the Qs to get the total Discharge for the stream.
Take Home Messages
• Understand the interactions between land use/land cover and components of the hydrologic cycle
• Be able to describe what is typically measured in watersheds and why
• Be aware of Washington stream types and how they are used in management