1. Scope

1.1 Rainfall simulators are used in the experimental process of erosion testing and performance testing of erosion control products. Quantification of the raindrop size is an important component of understanding the conditions applied to the test plot. 1.2 This test method is used to determine raindrop size of simulated rainfall using the flour pan method and is based on Laws and Parsons and Bentley. In the measurement of sediment yield from rainfall-induced erosion facilities, it is necessary to measure the size of the raindrops to compute the applied kinetic energy and calibrate the consistency of the applied rainfall within the simulator. Various test plot configurations exist each having their own specific parameters. This test method is intended to provide a means of measuring the raindrop size so the facility can demonstrate the simulator is providing the required raindrop size and consistency. 1.3 Testing standards requiring the measurement of raindrop diameter typically specify a size as part of the facility calibration. In performing the procedure listed herein, the raindrop size measured may or may not meet the requirements specified by the testing standard. Rather, this test method allows for the determination of raindrop size for the adjustment of the rainfall simulator until the specified raindrop size is achieved. It is outside the scope of this test method to specify any particular raindrop size. 1.4 UnitsThe values stated in either inch-pound units or SI units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. Reporting of test results in units other than inch pound shall not be regarded as nonconformance with this standard. 1.4.1The gravitational system of inch-pound units is used when dealing with inch-pound units. In the system, the pound (lbf) represents a unit of force (weight), while the units for mass is slugs. The slug unit is not given, unless dynamic (F = ma) calculations are involved. 1.4.2 The SI units presented for apparatus are substitutions of the inch-pound units. Other similar SI units should be acceptable providing they meet the technical requirements established by the inch-pound apparatus. 1.4.3 Calculations are performed using only one set of units, either gravitational inch-pound or SI. Alternate units are permissible provided appropriate conversion factors are used to maintain consistency of units throughout the calculation and similar significant digits or resolution or both are maintained. 1.4.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026. 1.4.5 The procedures used to specify how data are collected/recorded or calculated in the standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the users objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering data. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Keywords

erosion control; erosion control products; flour pan; raindrop size; rainfall simulator

Rationale

This test method is needed for determining simulated raindrop size at laboratories.

The title and scope are in draft form and are under development within this ASTM Committee.