Longitudinal Changes in Streams
• Certain characteristics of streams change predictably from upstream to downsteam– Channels become
wider– Flow becomes
slower, but greater in volume
– Streams become deeper
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Longitudinal Changes – Reach Scale
• Longitudinal changes are also observed at shorter scales than the entire river length
• We call this shorter scale the “reach” scale
• One example of reach scale changes is the pool-riffle pattern found in many streams draining areas with medium gradient
• Riffle is an area of rapid flow over coarse substrate (rocks) whereas the pool is a slower flowing stretch with finer substrate
• Path of flow - thalweg
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Lateral Patterns• There are also some
predictable changes laterally
• The stream has a low flow channel; the fastest flow is called the thalweg
• The stream has banks which define its frequent flow limit
• The stream has a floodplain which defines its flow limit on less frequent events, annual or lesser frequency
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Lateral Patterns
• Some streams and rivers will have a single dominant channel while others will have a network of interwoven channels
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Vertical dimensions
• Velocity changes with depth in stream channel• Discharge (Q) = VA
Diagram by:Eric G. PatersonDepartment of Mechanical and Nuclear EngineeringThe Pennsylvania State University
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Vertical Features
• Hyporheic (below stream) inter-actions
• Exchanges occur with groundwater just below the stream
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Lateral and Vertical Patterns
• In many large alluvial valleys, creatures that live in ground water and hyporheic water can be found in the subsurface water kilometers from the stream. In other words the stream extends well beyond its channel.
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Temporal dimension
• Stream flow changesSecond by secondHourlyDailyMonthlySeasonallyAnnuallyMilleniumly
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Selected Important Habitat Factors
• Substrate• Temperature• Oxygen levels• Flow velocity• Food availability• pH• Nutrient and sediment regimes• Organic input and transport
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How are species distributed in space and time?
-- Environments contributing to riverine biodiversity
Surface water Subsurface water Riparian system
Streams
Springs
LakesHyporheic
ZoneGroundWater
ConfinedReaches
UnconfinedReaches
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River --------------------------------------------- Floodplain Edge
Spatial distribution of species across a floodplain (lateral dimension)
Species Richness
0
50
100
Per
cen
t o
f m
axim
um
ric
hn
ess
fish
Mollusca
Odonata
Amphibia
Macrophytes
(Ward and Tockner 2001 fig. 9.3)
Species Richness
0
100
Eg.FishSnails, slugs, mussels,Dragonflies, damselfliesFrogs, salamanders, toadsAquatic plants
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Human caused disturbances
• Agriculture
• Timber harvest
• Mining
• Urbanization
• Introduction of exotic species
• Harvesting of fish and wildlife
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Land use/cover and vegetation
Physiography Climate
Landscape controls
NutrientInputs
Solar energy and
Organic input Regime
Gross reachmorphology
Habitat FormingProcesses
Species assemblages
Stream Morphology andConditions
Biodiversity
Habitat complexes and conditionse.g., pools, riffles, temperature, etc.
Sedimentand HydrologicRegime
Modified from Roni et al. 2002.
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Physical, chemical, and biological components related to water quality
• Light• Temperature• Dissolved ions• Suspended solids• Nutrients and gases• Toxics such as metals and pesticides/herbicides• Biological features• PPCPs (Pharmaceuticals & Personal Care Products)
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Forestry, agriculture and urbanization
• Remove trees and other vegetation
• Reduce organic matter delivery
• Build roads
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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
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How do we manage watershed?
• Dept of Natural Resources Regulations
• U.S. Forest Service Regulations
• Clean water act
• Endangered Species Act
• Total Maximum Daily Loads (TMDLs)
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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
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