Streamflow, Stream Shape

and

Connectivity in Watersheds

In This Presentation

Physical conditions within a watershed that can significantly impact water quality:

I) Streamflow

II) Channel shape

III) Connectivity (linkage of physical, chemical, biological conditions) within a watershed

I. Stream Flow

Streamflow:

• Part of the hydrologic cycle

• Water that comes together in a channel from:

Precipitation Storage Groundwater Wetlands Lakes

What is a hydrograph?

A graphic plot showing streamflow in a watershed during a runoff-producing event

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Data courtesy of High Island Creek Watershed Project

Stream Order

• Basins and watersheds contain streams of different sizes and locations

• Stream order is a way of categorizing, describing streams according to their size

Stream Order

• Numbered from 1-10• First order: “fledgling

streams” (springs, seeps, bogs, lakes)

• Second order: When two first order stream meets, resulting flow is second order stream

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Stream Order

• Smallest streams are 1st order

• The larger the stream, the higher the stream order

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• First order streams – often only a trickle (valuable for ecological attenuation)

• Fourth and Fifth Order streams -- for swimming, anglers and canoeists

• Tenth order – The lower Mississippi River (used by industry for transporation)

Photo: B.L. Johnson, USGS

Influences on Stream Flow

• Weather conditions and amount of precipitation affect flow

• Streamflow affected by seasonal patterns of precipitation, prior conditions, intensity of precipitation and temperature)

Influence of Weather on Streamflow

• Climate is often, but not always the predominant influence on streamflow.

• Amount of precipitation impacts volume of flow• Seasonal timing of snow, snowmelt, major

rainfall, and dry periods determine the seasonal pattern of streamflow (seasonal variability)

Influence of Weather on Streamflow

Snowmelt and spring storms often correspond with the highest streamflows

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Influence of Climate on Streamflow

During winter, streams are fed by groundwater, lakes and wetlands (base flow)

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Streamflow Patterns Change Across Seasons

• Each stream has a typical flow pattern throughout the year

• Streams with significantly different watershed characteristics will exhibit different hydrographs

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Hydrograph Depicts Changes in Streamflow Over Seasons

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Streamflow Changes Across Yearsc/

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Physical Characteristics of a Watershed

• Topography of a watershed also affects flow into a stream

• Steep hills drain quickly

Topography and Streamflow

Flat terrain drains water more slowly

Streamflow and Subsurface Flow

Water stored in soils above the stream channel contributes to flow downstream due to displacement

Water stored in uplands is displaced by new precipitation

Water Displacement and Streamflow

Analogy – When turning on a garden hose warmed by the sun, cold water eventually displaces warm water in the hose. Similarly, new water eventually displaces old water

in a watershed.

Uplands

River/Stream

Loss of Vegetation Affects Streamflow

• Plant cover affects amount, timing and quality of flow into streams

• Runoff over bedrock or barren soils is quicker

• Flow through grassy, cropped or forested areas is slower

• Lack of organic matter (crops, vegetation) increases surface runoff significantly

Vegetative Cover Affects Stream Flow

Vegetative Cover Affects Stream Flow

Land Use Affects Streamflow

Human activities greatly affect streamflow:

1. Wetland drainage

2. Agricultural drainage

3. Home construction

4. Road building

5. Agriculture

6. Clear-cutting of forests

7. Etc. What do these pictures have in common?

Effects on Land Use Changes on Flow

1. Changes in vegetative cover

2. Reductions in infiltration capabilities of soils

3. Alteration of stream channel or land slope

4. Loss of retention/detention storage

5. Increased channelization of streams

II. Channel Shape

Geomorphology

The study of the geologic forces that shape our landscape largely through the

action and effects of moving water

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Large-scale Geologic Forces Shape the Land

• Volcanoes, earthquakes, glaciers, and deposition are all forces that can form a landscape over which water flows

• Water flowing over different landscapes typically responds differently

• Geologic forces continue to shape the landscape (Question: At what rate?)

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Geology, Soils and Streamflow

How does geomorphology affect streamflow?

Examples:

Outwash Sand High Infiltration vs.Lacustrine Clay Low Infiltration

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Carbonate Bedrock High Infiltration vs. Igneous Bedrock Low Infiltration

Small Scale Geologic Forces Shape Stream Channels

Involves the interplay between the hydraulic force of moving water and the physical characteristics of the stream channel

-erosion

- deposition - resuspension - channel stability

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Stream Channel Shape and Function

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Nearly all channels are formed, maintained, and altered by the water and sediment they carry

Bankfull Flows Define River’s Shape

• Floods are not the most important flow situation in a stream channel

• Bank-full flows typically define a river’s shape

• Bank-full refers to the water level stage that just begins to spill out of the channel into the floodplain, occurring about every 2.3 years (averaged over wet and dry years)

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Stream Channel Change

Changes in streamflow regimes, channel modifications and floodplain alterations can collectively cause channel shape to change

The Shape of a Stream Channel Depends on 10 Variables

Flow• Channel width• Channel depth• Water velocity• Channel slope• Channel discharge

Resistance of Flow• Channel roughness• Sediment load• Sediment size• Material shear stress• Vegetation

Changes in any of these variables will affect degradation or aggradation and thereby the channel

form!

(Adapted from Leopold et. al. 1964)

II. Channel Shape and Equilibrium

Channel equilibrium occurs when all variables are in balance

System Dynamic Equilibrium

Alluvial streams flow in quasi-dynamic equilibrium where sediment load is transported in a manner that neither aggrades nor degrades

•Sediment transport occurs in a sustainable balance

System Dynamic Disequilibrium

• Geotechnical Processes

•Hydraulic Adjustment

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Channel Classification by Shape

II. Predictable Types of Channel Formation

Examples of Channel Shape

• Prairie River

• Bedrock River

• Ditch

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There Can Be Many Stream Shapes in One Watershed

Why Stream Classification Matters

Note:

• Stream systems are inherently complex

• By placing streams into a classification system, we can understand the processes that influence the pattern and character of the stream

Why Geomorphology Matters to TMDL Studies

Can help to determine:• The character of the watershed when it was

undisturbed• Current channel conditions• How the river is changing to accommodate changes

in flow volumes/duration, channel alteration etc.• How sediment is moving from upland sources to

downstream locations

Implications for TMDL Studies

• Stream classification allows us to predict a stream’s behavior such as:

sensitivity to disturbance recovery potential sediment supply potential for stream bank erosion, etc.

• This knowledge can help us in restoring stream systems

III. Connectivity

Linking the physical watershed

and stream channel to biological systems

Connectivity

• Within any watershed, there are physical, chemical and biological interactions that must be in balance

• If out of balance, it is impaired

• If in balance, stream is not impaired

Connectivity in Streams

• The flow, exchange and pathways that move organisms, energy and matter through a stream system

• A continuum of hydrologic, biological, and chemical interactions

• We must be able to link multiple disciplines and data sets in order to understand the “whole” we are trying to manage

Hydrodynamic Forces Create Diversity

• Within a stream, the variety of:

1. Channel width and depth variations

2. Substrates

3. Water velocities

supports a wide diversity of aquatic life

• Therefore, we must look at the whole stream, not just certain reaches

There Can Be Many Different Habitats Within One Stream

Physical Changes in the Shape of Rivers Affects Connectivity

Stream Channelization Consequences

1) Erosion of streambed upstream

2) Sedimentation downstream

3) Increased peak flows

4) Flooding downstream

5) Reduced biodiversity

Example:

Consequences of Increased Flow in a Stream

• Increased amount of surface runoff

• Streamflow rises faster and peaks at higher levels

• There is less base flow from groundwater

• Sediment disequilibrium

• Stream temperatures rise (generally)

And all of these affect stream life!

Changes in Land Use Affect Connectivity

• Natural river systems typically change gradually over time

• However, human activities on the land can cause swift, dramatic changes in erosion and sediment transport in a watershed

• Biological ecosystems are often negatively impacted

Other Impacts to Connectivity

• Dams• Persistent chemical or

thermal pollution• Invasion of exotic

species• Construction of

impervious surfaces• Water appropriations

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Changes in Land Use Affects Connectivity

Tim Larson