Development and testing of a large, transportable rainfall simulator for plot-scale runoff and parameter estimation

Abstract

Abstract. There is increased interest in the interplay between vegetation conditions and overland flow generation. The literature is unclear on this relationship, and there is little quantitative guidance for modeling efforts. Therefore, experimental efforts are needed, and these call for a lightweight transportable plot-scale (> 10 m 2 ) rainfall simulator that can be deployed quickly and quickly redeployed over various vegetation cover conditions. Accordingly, a variable-intensity rainfall simulator and collection system was designed and tested in the laboratory and in the field. The system was tested with three configurations of common pressure washing nozzles producing rainfall intensities of 62, 43, and 32 mm h −1 with uniformity coefficients of 76, 65, and 62 %, respectively, over a plot of 15.12 m 2 . Field tests were carried out on a grassy field with silt-loam soil in Orroli, Sardinia, in July and August 2010, and rainfall, soil moisture, and runoff data were collected. The two-term Philip infiltration model was used to find optimal values for the saturated hydraulic conductivity of the soil surface and bulk soil, soil water retention curve slope, and air entry suction head. Optimized hydraulic conductivity values were similar to both the measured final infiltration rate and literature values for saturated hydraulic conductivity. This inexpensive (less than USD 1000) rainfall simulator can therefore be used to identify field parameters needed for hydrologic modeling.

The Development of a Methodology for Calibrating a Large-Scale Laboratory Rainfall Simulator

“…The main purpose of an RS is to provide a reproducible collection of rainfall data as well as to accurately and precisely create a variety of rainfall regimes by controlling the rainfall intensity and duration [2,7,8]. The data collected from rainfall simulation experiments provide fundamental information to understand the dynamic behaviors of runoff generation, infiltration and soil erosion; this information is focused on how surface properties such as slope, soil properties, vegetation cover, and topography within catchments impact the above-mentioned processes [9,10].…”

“…There are also indoor and outdoor RSs according to transportability [7]. Small, portable field RSs can be useful due to their easy and rapid transport and implementation, but the small size generally limits their applications to accurate assessment of the net runoff response, including heterogeneity in surface properties at the plot scale [10]. On the other hand, laboratory RSs have been used to overcome the disadvantages of the small, portable field RSs [2,7].…”

“…This requires a laboratory RS that is sufficiently large to produce high rainfall intensities and that is suited to capture heterogeneity of surface properties across an experimental surface. Such measurements from a large laboratory RS can be used to increase the runoff response accuracy and precision of hydrological models [10]. Although additional research using large laboratory RSs is needed to assess the effects of surface property changes on the hydrologic cycle, simple and small RSs that produce rain over small areas (less than 5 m 2 and mostly less than 1 m 2 ) have been widely used [5,12,[25][26][27][28][29][30][31][32].…”

“…In addition to the desirable characteristics for precisely simulating rainfall, RSs need other requirements such as efficiency, simplicity, and economy [33]. However, it is difficult to meet the all requirements for RSs because there is a trade-off among the desirable characteristics such as size, cost, portability, areal coverage, ease of use, and operation [10,11,34]. The desirable features of RSs primarily depend on the research objectives and the rainfall characteristics required for specific research conditions.…”

The Uniformity Tests of A Rainfall Generator

“…Many kinds of rainfall simulators are developed and successfully used in soil erosion studies [4,5,6]. Some works have been published analyzing the characteristics of the artificial rainfall [7,8,9]. The following requirements are essential for rainfall simulators to be applied to the performance assessment of rain gauges: (1) the similar parameters such as drop size distribution, drop terminal velocity between the artificial and natural rainfall, (2) the time stability of artificial rainfall during one experiment, (3) homogeneous spatial rainfall distribution.…”