Watershed Assessment and Diagnosis of

Conditionfor

August 20, 2007

Joe Magner and Greg Johnson MPCA

Participants’ Background

• Watershed management and/or hydrology coursework?

• Watershed and/or hydrology work experience?

• Stream geomorphology training and/or experience?

• MnDNR’s Healthy Rivers Water Course?

• Other?

Assessment of What?

Condition of What?

Water Quality

Chemistry

Biology

Hydrology

Habitat

Land Use

MPCA Activities

• Point Source Pollution

• Water Quality Standards– Chemistry– Aquatic Life Support

• Nonpoint Source Pollution

• TMDLs – Total Maximum Daily Loads

• Impaired Waters

Watershed Systems

Approach

to

TMDLs and Impaired Waters

A Watershed Approach Requires Understanding the “Whole”

• Watersheds are complex systems where everything is connected

– Begin by looking at the pieces,

– But then make sure to integrate them in order to see “the whole” of what we are trying to manage

Definition of a Watershed

“The total land area from which water drains to a particular stream, river, lake, or other point of interest”

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A watershed approach requires the integration of many different disciplines:

• Geology• Soils• Biology• Geography• Water Chemistry• Hydrology

Focus on hydrology basics today

-- Hydrologic cycle

-- Sources and pathways of flow in

watersheds

-- Storage and movement of water in

watershed

Overview of Basic Hydrologic Principles:

Hydrology

The occurrence, distribution, and movement of water both on and under the earth's surface

The Hydrologic Cycle Controls Water in the Environment

Sources of Water in a Watershed

• Precipitation

• Groundwater

• Storage (internal sources of water stored in lakes, wetlands, ponds, puddles, soil)

Kinds of Storage That Contribute to Watershed Hydrology

• Depression – any surface where water collects and either seeps or evaporates (lakes, wetlands, ponds, puddles)

• Channel – water held within the channel (stream, river)

• Soil Water– water held within soil profile

• Vegetation – used by plants

• Groundwater – saturated zone (aquifers)

Pathways for Water in a Watershed

• Various processes and pathways determine how much and how fast precipitation becomes stream flow

• The pathway from rainfall to stream flow involves a combination of surface and sub-surface flows

• Difficult to separate the various pathways of flow

of Flow in a Watershed

Channel InterceptionSurface Runoff

Infiltration andSubsurface Flow

Rainfall

Channel Storage

(Stream Flow)

Groundwater or base flow

Adapted from Ken Brooks, 2003

PathwaysET

Water table

Surface Water / Groundwater Interactions

• Ground and surface water are often treated as separate systems

• But, they are inextricably linked

• Pathways of interaction are complex

Groundwater Recharge and Discharge

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Groundwater Recharge• Recharge can occur in many

portions of a watershed and over large areas

Groundwater Discharge

Areal extent and hydraulic characteristics govern amounts of recharge and discharge

• Groundwater is often the major source of base flow in streams

• Groundwater discharges typically seen as springs or seeps

• Groundwater discharges to surface waters can greatly affect temperature, dissolved oxygen and other characteristics of water which can affect aquatic life

Gaining and Losing Stream Reaches

Water table

Groundwater Water table

Stream flow

Gaining stream reach Losing stream reach

While some stream reaches are fed by groundwater, other stream reaches feed aquifers

Summary• Hydrology is the science concerned with the

occurrence, distribution, and movement of water

• Hydrology is one part of a watershed systems approach

• A watershed approach involves integrating several scientific disciplines

• The actual pathway from rainfall to streamflow involves a combination of surface and sub-surface flows

• Water quantity and quality in an impaired waterbody can be influenced by managing hydrologic pathways

Why is hydrology important to TMDL Studies?

• To manage an impaired water, we must first understand the hydrology of the watershed

• Understanding hydrology is critical to understanding sources and pathways of pollutants to a waterbody

• Addressing water quality problems in waterbodies will often require managing hydrologic pathways

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“Rivers and the inhabitants of the watery elements are made for wise people to contemplate and for fools to pass without consideration.” ---Izaak Walton