Search

Foehn winds have been a focus of research in mid‐latitude mountainous regions for more than 150 years, where their onset is typically associated with warm, dry, and gusty winds. This research has now extended into high latitude regions, yet research of foehn winds in subtropical and tropical regions remains scarce. Here we present results from the first investigation of foehn winds in the subtropics of Southeast Queensland (SEQ), Australia. Analysis of meteorological records found that foehn winds occur throughout the year with peak frequency and duration in late winter (August) associated with the passage of shortwave troughs over southern Australia. Modeling of wind fields and atmospheric boundary layer conditions for three case studies was conducted using the Weather Research and Forecasting (WRF) model. Results showed foehn events in SEQ can be associated with mountain waves and hydraulic jump features in the lee of topographic barriers. Over lee slopes, acceleration of wind speeds and topographic channeling of foehn winds was found to occur, along with substantial increases in air temperature, and decreases in relative humidity. Warming of the foehn airstream is believed to occur primarily through isentropic drawdown with a likely contribution from surface sensible heat flux. Recommendations for future research are made in light of the importance of foehn winds to wildfire management and mitigation in SEQ. Plain Language Summary: Foehn winds form as airflow associated with the passage of large‐scale weather systems descends over the lee slopes of mountains and escarpments. These warm, dry, and gusty winds significantly change the meteorology in the lee of mountains and escarpments causing increases in air temperature, wind speed and decreases in humidity. While foehn winds have been a focus of mountain meteorology in mid‐latitude regions for more than 150 years, research of foehn in other climate zones is scarce. Here we present results from the first investigation of foehn winds in the subtropics of Southeast Queensland (SEQ), Australia—a region where foehn winds significantly increase the threat of wildfires. Results show that foehn winds in this region are most common in late winter (August) with the passage of shortwave troughs over southern Australia. Using the Weather Research and Forecasting (WRF) model we find that foehn wind events in SEQ may be associated with mountain waves and other dynamical features in the lee of topography. We suggest avenues for future foehn wind research in SEQ given their importance to wildfire management and mitigation. Key Points: Subtropical foehn winds are accurately modeled using the Weather Research of Forecasting modelFoehn warming of +10 to +14°C was simulated and caused by isentropic drawdownModeling showed mountain wave and hydraulic jump features in trans‐barrier flow [ABSTRACT FROM AUTHOR]

The movements of fishes in natural river systems are affected by in-stream man-made structures, including dams and weirs. The effect of downstream fish passage over dam spillways has received little attention to date. In 2010, some observations of downstream fish passage were conducted at the Paradise Dam spillway, Australia during two markedly different flood events. The spillway was equipped with an un-gated crest, a steep stepped chute and a hydraulic jump energy dissipator without baffle block. The data on downstream fish passage at Paradise Dam are herein re-analysed with a focus on downstream fish passage over the spillway and associated mortality, together with some complementary information on the spillway operation. The mortality rates of fish passing on the Paradise Dam stepped spillway were very low. Under skimming flow conditions, the relative mortality rate was 0.085% of fish passing over the spillway on 3–4 March 2010. A higher mortality rate was seen under nappe flow conditions, although comparable to smooth chute fish mortality data. In average, the fish mortality data downstream of the Paradise Dam spillway was between 7 and 27 times lower than the natural fish mortality in the reservoir. Overall, the present data analyses demonstrated un-equivocally the significance of the spillway flow regime on the downstream fish passage mortality rate. It showed the adverse impact on fish during downstream passage at very-low flows, i.e. q < 0.01–0.02 m2.s−1, with both smooth-invert and stepped invert spillways. The finding highlighted a need for efficient downstream fish-friendly passage designs, adapted to the relevant spillway designs, and a number of low-flow fish-friendly channel designs are discussed. [ABSTRACT FROM AUTHOR]