News & Events

Noon seminar - Stream temperature and the need for thermal-dynamic sediment transport models

Monday, November 05, 2018, 12:15PM - 1:15PM

Speaker

Jaia Syvitski

INSTAAR

Location:

SEEC room S228 (Sievers Room)

Spatial and temporal variability of planetary parameters used in transport calculations are explored, with focus on stream temperature. Stream temperatures reflect latitudinal and seasonal variations in solar radiation, wind patterns, and water sources, and can be cooler or warmer than air temperatures. Tropical-equatorial rivers (e.g., Amazon, Congo) offer Earth’s smallest temperature variation (s <2°C, range <15°C); large temperate and sub-polar rivers (e.g., Mississippi, Lena) have the highest temperature variation (s >8°C, range >25°C). Variability in gravity and fluid density typically have minimal impact on sediment transport magnitude (<2%).  Kinematic viscosity has a global range of 72.5% and reduces sediment transport as stream temperatures warm. A 25°C increase, from stream descent, or flow to warmer latitudes, or seasonal increases, can increase grain settling velocities by 7.3%, 42%, 85%, 90% respectively for a 1000-µm, 250-µm, 62.5-µm, or a 10-µm grain, and reduce sediment transport by 90% for a grain population centered at 62.5 µm, or 300% if centered at 10µm. The common practice of using parameter constants (g =9.81 m/s2, rf =1000 kg/m3, T = 20°C), can greatly under-predict subpolar and alpine river transport and over-predict tropical stream transport. Temperature variations will affect rivers that transport a preponderance of finer sediment, a characteristic of most large rivers.

Coffee hour

Refreshments will precede the talk starting at 11:45.

Audience

Free and open to the public.