Discharge (Q) Define (cfs; m 3 /s or “cumecs”) Why is Q Important? How is it measured?

What is the usefulness of Q? Calculation of mass loading (L = Q*C) Calculation of mass loading (L = Q*C) Stream power determination (Q & slope) Stream power determination (Q & slope) Infer watershed hydrodynamics: Infer watershed hydrodynamics: Shape of storm event hydrograph Shape of storm event hydrograph Watershed characteristics. Watershed characteristics. Predominant water source of streams. Predominant water source of streams. Interannual hydrograph Interannual hydrograph Flood frequency and magnitude Flood frequency and magnitude Changing conditions, e.g., land-use impacts. Changing conditions, e.g., land-use impacts. Modeling and forecasting water resource needs. Modeling and forecasting water resource needs.

Hydrographs Plot of Q over time; Plot of Q over time; Peak(s) with a storm event. Peak(s) with a storm event.

Watershed Morphology Longitudinal profile (changing slope) Longitudinal profile (changing slope) Basin shape and timing of peak flow. Basin shape and timing of peak flow.

Downstream progression Crotty Cr. = 1.2 km2 Crotty Cr. = 1.2 km2 Acheron R. = 619 km2 Acheron R. = 619 km2 Goulbon R. = 8601 km2 Goulbon R. = 8601 km2

Groundwater supply in the Au Sable R. Groundwater supply in the Au Sable R. Runoff supply in the Raisin R. Runoff supply in the Raisin R. Note spring rain storms. Note spring rain storms. WaterSupply

More People; more development; less infiltration = flashy watershed Q Time after rain storm → Urban stream Forested Stream Why the change in baseflow?

Urbanization Senaca Creek, MD Greater maximum discharge for storm events of similar frequency before and after urbanization.

Dam Impacts Lower Missouri R. Lower Missouri R. Dammed in 1950s. Dammed in 1950s. Variability reduced. Variability reduced. Q controlled for barges. Q controlled for barges.

Changing Interannual conditions: Climate vs Land-use Acheron

How is Q measured? Direct Volumetric (L/s) Direct Volumetric (L/s) “V”-notch Weir “V”-notch Weir Dye Dilution Dye Dilution Velocity x Area Velocity x Area Stage to Discharge Stage to Discharge Manning’s Equation Manning’s Equation

“V”=notch Weirs Calibrate artificial structure. Brakensiek Equation: Q = H 2.48

Dye Dilution Estimates of Q Dye Slug vs Continuous Addition Dye Slug vs Continuous Addition Concentration of added dye is known. Concentration of added dye is known. Concentration is measured in stream over time. Concentration is measured in stream over time.

Q = Area x Velocity Measure height to cable per interval. Measure height to cable per interval. Note height to cable for “wet in” and “wet out”. Note height to cable for “wet in” and “wet out”. Measure velocity per interval. Measure velocity per interval. Calculate Q i ; i.e. discharge per interval. Calculate Q i ; i.e. discharge per interval. Q =  Q i Q =  Q i

Velocity Methods Manually timed distance: Manually timed distance: Near-neutrally buoyant floats Near-neutrally buoyant floats Dyes Dyes Current meters: Current meters: Mechanical (propeller or cups) Mechanical (propeller or cups) Electromagnetic (our FlowMate) Electromagnetic (our FlowMate) Acoustic Doppler Acoustic Doppler

Continuous Monitoring of Q “The Q Rating Curve” Water height (Stage) vs Q relationship. Water height (Stage) vs Q relationship. Stage determined by staff plate. Stage determined by staff plate. Stage by float mechanism. Stage by float mechanism. Stage by pressure gauge: Stage by pressure gauge: Incorporated in a water quality Sonde Incorporated in a water quality Sonde Requires correction for or venting for barometric pressure changes. Requires correction for or venting for barometric pressure changes.

Manning’s Equation Q = 1/n AR 2/3 S 1/2 A = cross-section area A = cross-section area S = longitudinal slope of channel S = longitudinal slope of channel n = Manning’s n n = Manning’s n (bottom friction constant)

Manning’s n n = (n 0 + n 1 + n 2 + n 3 + n 4 )m 5