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 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 c/o MDNR

Stream Order Smallest streams are 1 st order The larger the stream, the higher the stream order c/o MDNR

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

Streamflow Usually Declines in Summer c/o Metropolitan Council

Influence of Climate on Streamflow During winter, streams are fed by groundwater, lakes and wetlands (base flow) ©Explore MN Tourism

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 Stream at low flow Same stream at high flow c/o MnDNR

Hydrograph Depicts Changes in Streamflow Over Seasons c/o MnDNR

Streamflow Changes Across Years c/o MnDNR

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

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 ©Explore MN Tourism

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?) Photo: USGS c/o USGS

Geology, Soils and Streamflow How does geomorphology affect streamflow? Examples: Outwash Sand High Infiltration vs. Lacustrine Clay Low Infiltration ____________________________________________________ Carbonate Bedrock High Infiltration vs. Igneous Bedrock Low Infiltration

Small Scale Geologic Forces Shape Stream Channels I nvolves the interplay between the hydraulic force of moving water and the physical characteristics of the stream channel - erosion - deposition - resuspension - channel stability Joe Magner

Stream Channel Shape and Function c/o US EPA Watershed Academy 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) c/o MnDNR

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 Both Joe Magner

Channel Classification by Shape

II. Predictable Types of Channel Formation

Examples of Channel Shape Prairie River Bedrock River Ditch ©Explore MN Tourism Joe Magner ©Explore MN Tourism Pat Baskfield

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 ChannelizationConsequences 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 USGS c/o MnDNR c/o USGS

Changes in Land Use Affects Connectivity Tim Larson