ESSP 460/460L images HydraulicsHydraulics and Stream Morphology (seeing hydraulics in the field) For image re-use please reference Doug Smith (March 2003, CSUMB) Doug Smith CSUMB 1)Water is incompressible (Q=VA). 2) Water has high tensile strength---It does not "break apart" when it is stretched during acceleration (hydraulic drop). 3) Water has no shear strength---It flows under even a tiny applied stress (hydraulic jump). 4) Swiftly flowing water shears the mobile bed (sediment and large woody debris), producing sinuosity and bedforms that negatively feedback to control velocity. The bedforms include ripples, dunes, point-bars, riffle-pool sequences, step-pool sequences, and cascades.

Stream type? Hydraulics? Note the “boils” in the pools. Water is incompressible, so Q=VA at every cross section along the stream. AND Q is constant…as long as there are no significant springs, tributaries, or infiltration sinks along the reach.

Note water “stretching” but not “breaking” as it flows over the weir.. High “tensile strength” allows water to flow into smooth ribbons…typical of super-critical flow

Hydraulics? Very low “shear” strength allows tongue of high V water to underthrust and penetrate slower water ahead.

“Hydraulic jump” occurs when supercritical water runs into subcritical water. The tongue of rapid water pulls air down into the slower water….makes rapids. hydraulic jump subcritical supercritical critical subcritical

Stream type? Note boundary between critical and subcritical flow Standing waves indicating that V = (gD)^.5 Froude = 1 Critical flow

“Standing waves” and “antidunes Water flowing over a mobile bed makes ripples,dunes, and other bedforms that extract flow energy (add roughness) in a negative feedback loop to control stream velocity the following movies are large files (6-8 Mb) See a movie about dunes See a movie about antidunes

Stream type? Bedforms are caused by flowing water on a mobile bed… They are naturally- formed roughness elements that grow until they are in equilibrium with the flow… They pull energy from the flowing water

Large bedforms, called “steps” naturally form on a steep gradient stream. These are huge roughness elements that negatively feedback with velocity Large Woody Debris is one key element that forms “steps” in a steep reach. Flow kinetic energy is naturally dissipated as the water becomes very turbulent at hydraulic jumps. The kinetic energy is converted to work (erosion and sediment transport) and heat.

Stream type? Stream type mimic? Hydraulics? Purpose? Discussion?

Basic design for a step-pool stream Modified from Rosgen Note concave steps for flow concentration and pool for energy dissipation scour

Stream type? Hydraulics? Note concave shape of natural step…converges flow toward center of channel, maintaining a small scour hole

Hydraulics? Floodplain roughness elements in the southeast Tupelo- Cypress bottomland hardwood forest

Willow Posts Calebs Creek, TN ADDING ROUGHNESS among other things

Stream type? Hydraulics? Natural roughness elements provide diversity of hydraulics and therefore diversity of habitat. floodplain pool riffle bankfull

Stream type? Hydraulics? Gablan “Creek” where it is controlled by agriculture

Stream type? C-something Hydraulics? Subcritical turbulent flow--tranquil

Hydraulics?

Stream type? Hydraulics? Broad-crested weir Critical flow Vc = (g Dc)^0.5 So, if the flow depth is.08 m, the Vc =.89 m/s jump Stream type? Hydraulics? Subcritical flow

Sharp-crested wier for estimating V to get Q Measure specific head (H) ….Dc=2/3H Vc = (9.8 Dc)^0.5

Assorted vanes Bank protection, grade control, sediment transport, Habitat, chemistry (oxygenation)

J-hook vanes

W-weirs & Wing deflectors San Juan River Bank protection, grade control, sediment transport, habitat, oxygenation & recreational boating

1)Set the distance 2)Read the water depth 3)Set the probe depth to 60% of water depth 4)Reset the electronics 5)Stand away from the meter 6)Push start button 7)Record revolutions 8)repeat Basics of using a flow meter See class notes, Harrelson et al., And USGS for details

Stream type? Hydraulics? ESSP … Natividad Creek… Heading for bankfull in a storm