Watersheds and Hydrology

Watersheds and Hydrology What’s Water Got to Do with It? • More water moves through ecosystems than any other material • The materials that it carries and deposits and the energy that it expends are major drivers in shaping the contour of the land and the habitat availability/suitability for organisms. • A resource that humans cannot live without

Watersheds andHydrologyLearning Objectives • Where do we find water? • What is the hydrologic cycle? • How many dimensions does a stream have? 4 How do we characterize stream water? 5 What do we want to know about stream flow?

Question 1 Where do we find water?

Global distribution of water

Global distribution of freshwater

Watersheds andHydrology • Where do we find water? • What is the hydrologic cycle? • How many dimensions does a stream have? 4 How do we characterize stream water? 5 What do we want to know about stream flow?

Question 2What is the hydrologic cycle? What is the hydrologic cycle? Precipitation Interception Infiltration Evaporation Transpiration Runoff Ground water

Question 3 How many dimensions does a stream have?

Question 3 How many dimensions does a stream have? • Longitudinal (upstream to downstream) • Lateral (bank to bank and valley wall to valley wall) • Vertical (water surface to bed to hyporheic to ground water) • Temporal (time: seconds to millennia)

Longitudinal Changes in Streams • Certain characteristics of streams change ‘predictably’ from upstream to downsteam • Channels become wider • Channels become deeper • Flow becomes slower, but greater in volume

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 gradients • Riffle is an area of rapid flow over coarse substrate (sediment) whereas the pool is a slower flowing stretch with finer substrate

Lateral Patterns • There are also some predictable changes laterally • The stream has its low flow channel, the low point of which is 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 Thalweg

Lateral Patterns • Some streams and rivers will have a single dominant channel while others have a network of interwoven channels

Lateral Features • As rivers increase in size they will develop a complex floodplain system

Vertical dimensions • Velocity changes with depth in stream channel Diagram by:Eric G. Paterson Department of Mechanical and Nuclear Engineering The Pennsylvania State University

Vertical Features • Hyporheic (below stream) inter-actions • Exchanges occur with groundwater just below the stream

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 visible channel.

Temporal dimension • Stream flow changes Second by second Hourly Daily Monthly Seasonally Annually Millenniumly • Channels migrate • Riparian areas go through disturbance and succession • Seasonal changes in inputs

What are the major physical, chemical, and biological components used to characterize water quality?

Selected Important Habitat Factors • Light • Substrate • Temperature • Oxygen levels • Flow velocity • Food availability • pH • Hydrologic, nutrient and sediment regimes • Organic input and transport • Toxics and other pollutants • Biological communities

Influence of temperature on growth rates 1.0 Midges Daily Growth Rate (mg/day) 0.5 Blackflies Mayflies 0 0 8 16 24 32 Temperature C Modified from Benke 1993

What do we want to know about stream flow? Question 5 • Magnitude - how much? • Frequency - how often? • Timing - when? • Duration - how long? • Rate of change – how fast?

1982

Mean daily flow (cfs)Juanita Creek Water Year 2010 Oct May

Mean Monthly FlowsJuanita Creek Water Years 2005-2009

Oct 13 midnight Oct 12 midnight

Mean Daily FlowJuanita Creek (cfs)

15 minute flowsJuanita Creek May 27-29, 2004 May 28

Unregulated Regulated

How much water is enough? • Depends on who or what is using the water • Historically managed for minimum flows (what is the minimum flow that keeps fish alive) • Legal issue of water rights complicates situation

Examples of where to locate national data for watersheds and streams • Watershed data • EPA Surf your watershed http://www.epa.gov/surf/ • Climate data (national and international) http://www.ncdc.noaa.gov/oa/ncdc.html • Climate data (Washington) http://www.wrcc.dri.edu/summary/climsmwa.html

Examples of where to locate national data for watersheds and streams • Stream data- quantity and quality • USGS Water Resources Data http://water.usgs.gov/data.html • Soils data • http://soils.usda.gov/ • Aquatic biologic indicators • http://www.epa.gov/bioindicators/

Take – home messages • Flow regimes play a major role in habitat • Land-use alters flow paths and storage components and hence, flow regimes • Effects vary with spatial and temporal scales • Research on which aspects of flow are most critical to various biotic responses are in progress • Don’t forget the basic processes involved

Watersheds and Hydrology