Introduction to Watershed Hydrology RACC High School Training

Introduction to Watershed Hydrology RACC High School Training June 26, 2012 Jody Stryker University of Vermont

What is a watershed? • An area of land that drains water, sediment, and dissolved materials to a common outlet. • Watershed are separated by drainage divides. • Can be any shape and size. • Sub-watershed = watershed within a watershed. LEGEND flow lines sub-watersheds Elevation “Watershed” = “catchment” = “drainage basin”

Within a watershed Image credit: Watershed Activities to Encourage Restoration, http: //www. watershedactivities. com/projects/fall/h 2 omodel. html

What happens downstream? Image credit: NOAA Figures show dead zone near mouth of Mississippi River, Gulf of Mexico. Image credit: APA News/NASA

Stream order Headwaters Confluences Outlet Image Credit: Developed by T. Endreny at SUNY ESF in the Department of Environmental Resources Engineering

Global hydrologic cycle Figure credit: URI Water Quality Home

Rainfall to runoff Precipitation Transpiration Interception by canopy • Groundwater flow • Subsurface flow (interflow) • Overland flow Evaporation Stem-flow Overland runoff Root uptake Infiltration Subsurface flow Groundwater flow Infiltration

Runoff pathways • Groundwater flow • Subsurface flow (interflow) • Overland flow Source: M. Ritter, The Physical Environment.

Surface runoff is affected by. . . Climate characteristics such as: • Type of precipitation • Rainfall intensity • Rainfall duration • Rainfall distribution • Antecedent precipitation and soil moisture • . . . Source: M. Ritter, The Physical Environment.

Surface runoff is affected by. . . Physical characteristics such as: • Land use • Vegetation • Soil • Basin shape • Elevation • Slope • Topography • Drainage patterns • . . . Source: M. Ritter, The Physical Environment.

… landforms reflect dominant runoff processes V-shaped valley of a humid, temperate landscape Photo credit: Field Studies Council, UK Badland topography of an arid landscape Photo credit: National Park Service

Effects of development on runoff Image credit: Minnesota Center fro Environmental Advocacy

Effects of development on runoff Image credit: Minnesota Center fro Environmental Advocacy Natural Landscape ü Low runoff ü High infiltration and recharge ü Healthy summer stream flow ü Natural pollutant treatment Developed - High runoff, low recharge - Lower water tables - Low stream flow -Nuisance flooding

Measuring river runoff Steps: 1. Measure stream stage (height of water surface). 2. Measure discharge. 3. Define relationship between stage and discharge. Image credit: Vermont EPSCo. R CWDD , http: //www. uvm. edu/~streams/index_old. php? Content=pages/2010_2011_Undergraduates

Measuring river runoff Steps: 1. Measure stream stage (height of water surface). Diagram of a typical USGS stream gage with stilling well. Image credit: The USGS Water Science School , http: //ga. water. usgs. gov/edu/streamflow 1. html

Measuring river runoff 2. Measure discharge. Discharge = velocity * width * depth Image credit: The USGS Water Science School , http: //ga. water. usgs. gov/edu/streamflow 2. html Steps:

Image credit: The USGS Water Science School , http: //ga. water. usgs. gov/edu/streamflow 3. html Measuring river runoff Steps: 3. Define relationship between stage and discharge.

Hydrograph • A way to look at the response of a watershed to hydrologic event • Discharge (cms/cfs) vs. time • Comprised of base flow and direct flow

Hydrograph pattern is the result of: Image credit: BBC: Intermediate Geography Rivers Watershed characteristics

Hydrograph pattern is the result of: Climate • Humid vs. arid • Previous rainfall Storm characteristics • Intensity • Duration • Spatial distribution of events Image credit: http: //echo 2. epfl. ch/VICAIRE/mod_1 a/chapt_2/main. htm

Image credit: Battle River Watershed Alliance, CA.

Stream channel morphology Image credit: Fisheries and Oceans Canada, http: //www. pac. dfo-mpo. gc. ca/habitat/Glossary-glossaire-eng. htm

Stream morphology and stream health Image credit: Vermont Water Quality Division

Climate change and hydrology • What climate related changes might we see?

Climate change and hydrology • What climate related changes might we see? Higher surface temperatures Reduced snowpack Increased drought conditions Increase in regional precipitation – Longer growing seasons – Greater frequency of extreme events – –

Climate change and hydrology • What climate related changes might we see? Higher surface temperatures Reduced snowpack Increased drought conditions Increase in regional precipitation – Greater frequency of extreme events – – • What hydrologic changes might we see?

Climate change and hydrology • What climate related changes might we see? Higher surface temperatures Reduced snowpack Increased drought conditions Increase in regional precipitation – Greater frequency of extreme events – – • What hydrologic changes might we see? – Higher runoff – More erosion – Increased transportation of dissolved materials – Increased flooding frequency and/or magnitude – Geomorphic channel adjustments – More altered landscapes – Higher water demand

Climate change, hydrology, new challenges Image credit: Vermont Watershed Management Division Image credit: Vermont Agency for Natural Resources Image credit: Vermont Watershed Management Division

Hydrologic effects of deforestation/development Image credit: USGS, http: //ga. water. usgs. gov/edu/watercyclerunoff. html

An experiment • Sprinkle rainfall on “forested” watershed – collect runoff in cup • Deforest and develop your watershed • Sprinkle rainfall on “developed” watershed – collect runoff in cup

An experiment In each case consider: • How much of rainfall runs off? • How long before runoff begins at the bottom of the watershed? • What happens when rainfall stops?

Why does land use matter? Influences how much water runs off Influences how and where water runs off