Abstract
AbstractSiphons can effectively reduce the influence of rainfall intensity on the mechanical bias of tipping-bucket rain gauges (TBRs). To identify the function of siphons for TBRs, this study investigated three types of siphons: a Texas Electronics (TE) siphon, a RIMCO (RIM) siphon, and a Sutron siphon, with both computational fluid dynamics (CFD) simulations and laboratory experiments. To provide better structural designs, further simulations were conducted to adjust two parameters of the siphons: d, the distance from the cap to the outer part, and w, the distance from the main part to the cap part. The simulation results reveal that the most significant advantage of a siphon over a rain gauge collector is to provide stable outflow for the tipping bucket. The stable outflow rates were around 1.5 g s−1 (TE) and 1.55 g s−1 (RIM), while the Sutron siphon increased from 1.75 to 2.45 g s−1. The ratio of stable outflow time to a complete siphon event was 69% (TE), 81% (Sutron), and 83% (RIM). In experiments with rainfall intensity higher than 1 mm min−1, the RIM and TE siphons showed oscillations in the outflow during consecutive siphon events, whereas the Sutron siphon was relatively stable. Further simulations showed that the recommended d and w for the TE siphon are 2.5 and 1.1 mm, respectively, while the recommendations for the RIM siphon are d = 2.5 mm and w = 0.9 mm. The manufacturer’s specifications for d and w are best for the Sutron siphon. These results help to understand the functionality of siphons for TBRs, and benefit the structural design of common siphons.
Highlights
Tipping-bucket rain gauges (TBRs) are widely used in hydrology and meteorology to measure rainfall because they are simple, durable, inexpensive, and easy to install in urban and remote areas (Humphrey et al 1997; Fankhauser 1998; Shedekar et al 2016)
The outflow rate during the stable outflow stage was 1.5 g s21 for the Texas Electronics (TE) siphon and 1.55 g s21 for the RIM siphon
Two parameters (d, the distance between the cap part and the outer part, and w, the distance between the main part and the cap part) were tested in simulations to improve the structural design of siphons
Summary
Tipping-bucket rain gauges (TBRs) are widely used in hydrology and meteorology to measure rainfall because they are simple, durable, inexpensive, and easy to install in urban and remote areas (Humphrey et al 1997; Fankhauser 1998; Shedekar et al 2016). TBRs underestimate rainfall volume and intensity because of rainwater that is missed as the bucket flips (Molini et al 2005). A nonlinear relationship usually exists between rainfall intensity and raw volume measurements from the tipping bucket. To reduce the influence of rainfall intensity on the mechanical bias of TBRs, three main approaches have been adopted. The dynamic calibration method is often adopted to determine the relationship between the rainfall intensity and the raw measurement of the TBR, and a calibration relationship is used to correct the raw measurement (Calder and Kidd 1978; Niemczynowicz 1986; La Barbera et al 2002; Liao et al 2020)
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