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