ASTM D8326-21

Standard Practice for Measurement of the Kinetic Energy of Simulated Rainfall

SIGNIFICANCE AND USE
5.1 When a raindrop impacts the surface of a soil, it expends its energy and begins the impact-induced soil erosion process. This kinetic energy of the raindrop is one factor influencing soil erosion. This practice provides a method to quantify the kinetic energy produced by rainfall simulators.  
5.2 Soil erosion is a concern that affects many industries. The highway and road construction industry is particularly interested in slope protection. There are many ECP manufacturers that rely on testing of their products using rainfall simulators to meet certain specifications set forth by different agencies.  
5.3 Laboratories that offer testing of ECPs use rainfall simulators. Many laboratories are able to adjust their rainfall simulators, the drop height of the raindrops, and even the slopes of the test plots they use to model expected, anticipated, or actual field conditions. The kinetic energy associated with the specific configuration of the simulator should be measured.  
5.4 Knowing the kinetic energy for the given simulator configuration will provide a way to set minimum and upper limit values so that comparisons between laboratories can be made as well as having a way to account for the differences between the laboratories. If there are minimum and upper limit values and the raindrop size is in the same range between laboratories, the kinetic energy between the laboratories should be similar. Once the kinetic energy is established for a given rainfall simulator configuration according to a specific standard, comparisons of the results for those specific standards can be made.
Note 2: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Pract...
SCOPE
1.1 This practice is used to measure the kinetic energy of rainfall simulators used by laboratories to evaluate soil erosion. The kinetic energy of raindrops is an important factor that should be considered when conducting soil erosion studies. Using the data collected from determining the raindrop size, this practice provides a method to uniformly calculate the kinetic energy which can be used to compare results from different laboratories.  
1.2 Many types of Erosion Control Products (ECPs) are evaluated for their ability to reduce soil erosion in laboratory and field settings using rainfall simulators. Rainfall simulators are used with test plots to simulate a specific condition that is or may be expected in the field. Rainfall simulators typically use drop emitters, sprinklers, or nozzles to create the raindrops. Each device produces different drops and since the rainfall simulators can be configured to produce different raindrop sizes and fall heights, the kinetic energy will be different. Therefore, the kinetic energy must be calculated for a given set of conditions in order to properly understand the impact of erosion for bare soil and the ECP.  
1.3 The upper limit of the size of a raindrop is generally accepted to be 7 mm. While it is possible to get a raindrop size between 6 and 7 mm occasionally, it is not common to get raindrop sizes above 6 mm.  
1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.  
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.  
1.5.1 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 s...

General Information

• Status: Published
• Publication Date: 31-Dec-2020
• ICS: 13.080.01 - Soil quality and pedology in general
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.25 - Erosion and Sediment Control Technology

Relations

• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D8151-19 - Standard Practice for Obtaining Rainfall Runoff from Unvegetated Rolled and Hydraulic Erosion Control Products (RECPs and HECPs) for Acute Ecotoxicity Testing
• Effective Date: 15-Jun-2019
• Refers: ASTM D8151-19e1 - Standard Practice for Obtaining Rainfall Runoff from Unvegetated Rolled and Hydraulic Erosion Control Products (RECPs and HECPs) for Acute Ecotoxicity Testing
• Effective Date: 15-Jun-2019
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D3740-12a - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-May-2012
• Refers: ASTM D3740-12 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2012
• Refers: ASTM D3740-11 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Sep-2011
• Refers: ASTM D653-11 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Sep-2011
• Refers: ASTM D3740-10 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2010
• Refers: ASTM D653-09 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Jan-2009
• Refers: ASTM D653-08a - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Dec-2008
• Refers: ASTM D653-08 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Nov-2008
• Refers: ASTM D3740-08 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2008
• Refers: ASTM D653-07f - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 15-Dec-2007

Overview

ASTM D8326-21: Standard Practice for Measurement of the Kinetic Energy of Simulated Rainfall establishes a precise methodology for quantifying the kinetic energy of rainfall simulators in laboratory settings. The accurate measurement of raindrop kinetic energy is critical for evaluating rain-induced soil erosion and assessing the performance of Erosion Control Products (ECPs). This standardized practice enables consistent, comparable results across different laboratories and testing scenarios, supporting the needs of industries such as construction, transportation, and environmental protection that are concerned with soil stability and erosion mitigation.

Key Topics

• Kinetic Energy Measurement: The standard outlines procedures to measure the kinetic energy generated by artificially simulated rainfall, specifically from drop emitters, sprinklers, or nozzles.
• Raindrop Characteristics: Considers raindrop size (up to 7 mm) and drop height as primary variables affecting kinetic energy and soil erosion.
• Uniform Calculation Approach: Provides methods to calculate kinetic energy using SI units, ensuring reliable comparison of test results between laboratories.
• Laboratory Consistency: Addresses the need to establish minimum and maximum kinetic energy values for simulator configurations to ensure repeatability and reliability.
• Quality Assurance: Stresses the role of laboratory competence, personnel training, and equipment suitability in producing high-quality, standardized results.
• Test Reporting: Requires documentation of raindrop sizes, drop heights, test plot dimensions, and calculated kinetic energies, following industry best practices for data collection and reporting.

Applications

ASTM D8326-21 is applied in a range of soil erosion assessment scenarios:

• Erosion Control Product (ECP) Evaluation: Used by manufacturers and laboratories to test the effectiveness of ECPs under simulated rainfall conditions, which is crucial for regulatory compliance and product development.
• Highway and Road Construction: Assists engineers in assessing slope protection solutions by providing standardized rainfall impact data for bare soil and vegetated or treated slopes.
• Research and Development: Enables academic and industrial research focused on understanding erosion mechanics, comparing soil treatment methods, and optimizing simulator designs.
• Regulatory and Agency Compliance: Supports consistency in meeting agency specifications for environmental impact studies and construction projects requiring soil erosion control validation.
• Inter-laboratory Comparison: Facilitates benchmarking and quality control by allowing different laboratories to calibrate rainfall simulators to recognized kinetic energy ranges and directly compare test outcomes.

Related Standards

Several ASTM standards complement or are referenced by ASTM D8326-21, supporting comprehensive rainfall simulation and soil testing workflows:

• ASTM D653: Terminology Relating to Soil, Rock, and Contained Fluids. Provides a common vocabulary for interpreting soil and erosion-related standards.
• ASTM D3740: Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock. Covers laboratory competence and quality assurance.
• ASTM D6026: Practice for Using Significant Digits in Geotechnical Data. Specifies guidelines for rounding, reporting, and recording calculated and observed values.
• ASTM D8151: Practice for Obtaining Rainfall Runoff from Unvegetated Rolled and Hydraulic Erosion Control Products for Acute Ecotoxicity Testing. Offers guidance on measuring raindrop size and collecting relevant data during soil testing.

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Keywords: kinetic energy measurement, simulated rainfall, rainfall simulator, raindrop size, soil erosion, erosion control products, ASTM D8326-21, laboratory testing, environmental protection, construction standards

Standards Content (Sample)

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.
Designation: D8326 − 21
Standard Practice for
Measurement of the Kinetic Energy of Simulated Rainfall
This standard is issued under the fixed designation D8326; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope dures used do not consider material variation, purpose for
obtaining the data, special purpose studies, or any consider-
1.1 This practice is used to measure the kinetic energy of
ations for the user’s objectives; and it is common practice to
rainfallsimulatorsusedbylaboratoriestoevaluatesoilerosion.
increase or reduce significant digits of reported data to be
The kinetic energy of raindrops is an important factor that
commensuratewiththeseconsiderations.Itisbeyondthescope
should be considered when conducting soil erosion studies.
of this standard to consider significant digits used in analysis
Using the data collected from determining the raindrop size,
methods for engineering design.
this practice provides a method to uniformly calculate the
kinetic energy which can be used to compare results from 1.6 This practice offers a set of instructions for performing
different laboratories. one or more specific operations. This document cannot replace
educationorexperienceandshouldbeusedinconjunctionwith
1.2 Many types of Erosion Control Products (ECPs) are
professional judgment. Not all aspects of this practice may be
evaluated for their ability to reduce soil erosion in laboratory
applicable in all circumstances. This ASTM standard is not
and field settings using rainfall simulators. Rainfall simulators
intended to represent or replace the standard of care by which
are used with test plots to simulate a specific condition that is
the adequacy of a given professional service must be judged,
or may be expected in the field. Rainfall simulators typically
nor should this document be applied without consideration of
usedropemitters,sprinklers,ornozzlestocreatetheraindrops.
a project’s many unique aspects. The word “Standard” in the
Each device produces different drops and since the rainfall
title of this document means only that the document has been
simulators can be configured to produce different raindrop
approved through the ASTM consensus process.
sizes and fall heights, the kinetic energy will be different.
1.7 This standard does not purport to address all of the
Therefore, the kinetic energy must be calculated for a given set
safety concerns, if any, associated with its use. It is the
of conditions in order to properly understand the impact of
responsibility of the user of this standard to establish appro-
erosion for bare soil and the ECP.
priate safety, health, and environmental practices and deter-
1.3 The upper limit of the size of a raindrop is generally
mine the applicability of regulatory limitations prior to use.
accepted to be 7 mm. While it is possible to get a raindrop size
1.8 This international standard was developed in accor-
between 6 and 7 mm occasionally, it is not common to get
dance with internationally recognized principles on standard-
raindrop sizes above 6 mm.
ization established in the Decision on Principles for the
1.4 Units—The values stated in SI units are to be regarded
Development of International Standards, Guides and Recom-
as standard. No other units of measurement are included in this
mendations issued by the World Trade Organization Technical
standard. Reporting of test results in units other than SI shall
Barriers to Trade (TBT) Committee.
not be regarded as nonconformance with this standard.
2. Referenced Documents
1.5 All observed and calculated values shall conform to the
2.1 ASTM Standards:
guidelines for significant digits and rounding established in
D653 Terminology Relating to Soil, Rock, and Contained
Practice D6026.
Fluids
1.5.1 Theproceduresusedtospecifyhowdataarecollected/
D3740 Practice for Minimum Requirements for Agencies
recorded or calculated in the standard are regarded as the
Engaged in Testing and/or Inspection of Soil and Rock as
industry standard. In addition, they are representative of the
Used in Engineering Design and Construction
significant digits that generally should be retained. The proce-
D6026 Practice for Using Significant Digits in Geotechnical
Data
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.25 on Erosion and
Sediment Control Technology. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 1, 2021. Published January 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2020. Last previous edition approved in 2020 as D8326 - 20. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D8326-21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8326 − 21
NOTE 2—The quality of the result produced by this standard is
D8151 Practice for Obtaining Rainfall Runoff from Unveg-
dependent on the competence of the personnel performing it, and the
etated Rolled and Hydraulic Erosion Control Products
suitability of the equipment and facilities used. Agencies that meet the
(RECPs and HECPs) for Acute Ecotoxicity Testing
criteria of Practice D3740 are generally considered capable of competent
and objective testing/sampling/inspection/etc. Users of this standard are
3. Terminology
cautioned that compliance with Practice D3740 does not in itself assure
reliable results. Reliable results depend on many factors; Practice D3740
3.1 Definitions:
provides a means of evaluating some of those factors.
3.1.1 For definitions of common technical terms used in this
standard, refer to Terminology D653.
6. Apparatus
6.1 Raindrop Size—See Practice D8151 for the apparatus
4. Summary of Practice
needed to measure the raindrop size.
4.1 Before the kinetic energy can be measured, the raindrop
6.2 Measuring Device—A surveyor’s rod, tape measure, or
size and drop height must be determined (Note 1). The fall
similar with enough length and divisions of 5 mm or better to
velocities are also determined based on the drop height and the
measure the rainfall distance (drop height) and the test plot
diameters as shown inTableA1.1.The fall velocities are either
width (cross slope) and length (down slope).
interpolated or selected directly from the table and then the
raindropdiameterversusfallvelocityisgraphedandfittedwith
7. Procedure
a third degree (cubic) polynomial regression trend line to
7.1 Raindrop Size—Determine and record the range of
obtain the regression equation. The constant values from the
raindrop sizes to the nearest 0.001 mm of the rainfall simulator
regression equation are used to calculate the ground velocities
configuration used following the procedure in 8.4 of Practice
for each of the average raindrop diameters as measured. Once
D8151.
the ground velocity is determined, the various kinetic energy
values are calculated, including the kinetic energy of the
7.2 Drop Height—Determine and record the drop height of
simulated event.
the raindrops to the nearest 0.1 m of the rainfall simulator
configuration used. For inclined structures, the drop height is
NOTE 1—Subcommittee D18.25 is currently developing a standard
takentobefromtherainfallsimulatortothelowestpointofthe
method for determining the raindrop size independent of any other type of
testing. Until that standard is approved, Practice D8151 provides the incline structure.
information on how to obtain the raindrop size.
7.3 Test Plot Dimensions—Determine and record the width
(cross slope) and length (downslope) of the test plot to the
5. Significance and Use
nearest 0.1 m. Determine and record the area of the test plot,
5.1 Whenaraindropimpactsthesurfaceofasoil,itexpends
A , to the nearest 0.1 m .
tp
its energy and begins the impact-induced soil erosion process.
7.4 Cake Pan Dimensions—Determine and record the width
This kinetic energy of the raindrop is one factor influencing
andlengthofeachcakepanusedtocapturetheraindropstothe
soil erosion. This practice provides a method to quantify the
nearest 5 mm. Determine and record the area of each cake pan,
kinetic energy produced by rainfall simulators.
A , to the nearest 0.001 m . Determine and record the total
cp
5.2 Soil erosion is a concern that affects many industries.
area of the cake pans, A , to the nearest 0.001 m .
pan
The highway and road construction industry is particularly
7.5 Fall Velocity—Determine and record the fall velocities
interested in slope protection. There are many ECP manufac-
to the nearest 0.01 m/s based on the drop height using raindrop
turers that rely on testing of their products using rainfall
diameters of 1.25, 2, 3, 4, 5, and 6 mm and Table A1.1 (See
simulators to meet certain specifications set forth by different
Annex A1). Graph the raindrop size (abscissa) versus the fall
agencies.
velocities (ordinate) and fit a third degree (cubic) polynomial
5.3 Laboratories that offer testing of ECPs use rainfall
trend line to the data and record the regression equation. Table
simulators. Many laboratories are able to adjust their rainfall
1 provides the cubic regression data for commonly used drop
simulators, the drop height of the raindrops, and even the
slopes of the test plots they use to model expected, anticipated,
or actual field conditions. The kinetic energy associated with
TABLE 1 Cubic Regression Data for Commonly Used Drop
the specific configuration of the simulator should be measured.
Heights
5.4 Knowing the kinetic energy for the given simulator Drop Height ab c d
A
(m)
configuration will provide a way to set minimum and upper
2.4 0.0282 -0.4071 2.0914 2.3807
limit values so that comparisons between laboratories can be
3.4 0.0324 -0.4794 2.5539 2.1783
3.7 0.0320 -0.4803 2.6169 2.1715
made as well as having a way to account for the differences
4.0 0.0313 -0.4796 2.6731 2.1715
between the laboratories. If there are minimum and upper limit
4.3 0.0324 -0.5007 2.8028 2.0595
values and the raindrop size is in the same range between
4.6 0.0343 -0.5310 2.9686 1.9051
6.1 0.0397 -0.6330 3.5798 1.3095
laboratories,thekineticenergybetweenthelaboratoriesshould
A
be similar. Once the kinetic energy is established for a given The drop height in meters corresponds to the drop height in feet as follows: 2.4
m=8ft;3.4m=11ft;3.7m=12ft;4.0m=13ft;4.3m=14ft,4.6m=15;and
rainfall simulator configuration according to a specific
6.1m=20ft.Fordropheightsgreaterthan6.1m,thevelocityis considered
standard, comparisons of the results for those specific stan-
terminal.
dards can be made.
D8326 − 21
heights. For drop heights not listed in Table 1, refer to Annex 8.5 Calculate the kinetic energy of the simulated event,
A1 for instructions on obtaining the cubic regression data. KE , using the following equation
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D8326 − 20 D8326 − 21
Standard Practice for
Measurement of the Kinetic Energy of Simulated Rainfall
This standard is issued under the fixed designation D8326; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice is used to measure the kinetic energy of rainfall simulators used by laboratories to evaluate soil erosion. The
kinetic energy of raindrops is an important factor that should be considered when conducting soil erosion studies. Using the data
collected from determining the raindrop size, this practice provides a method to uniformly calculate the kinetic energy which can
be used to compare results from different laboratories.
1.2 Many types of Erosion Control Products (ECPs) are evaluated for their ability to reduce soil erosion in laboratory and field
settings using rainfall simulators. Rainfall simulators are used with test plots to simulate a specific condition that is or may be
expected in the field. Rainfall simulators typically use drop emitters, sprinklers, or nozzles to create the raindrops. Each device
produces different drops and since the rainfall simulators can be configured to produce different raindrop sizes and fall heights,
the kinetic energy will be different. Therefore, the kinetic energy must be calculated for a given set of conditions in order to
properly understand the impact of erosion for bare soil and the ECP.
1.3 The upper limit of the size of a raindrop is generally accepted to be 7 mm. While it is possible to get a raindrop size between
6 and 7 mm occasionally, it is not common to get raindrop sizes above 6 mm.
1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026.
1.5.1 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 user’s 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 design.
1.6 This practice offers a set of instructions for performing one or more specific operations. This document cannot replace
education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be
applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.25 on Erosion and Sediment
Control Technology.
Current edition approved July 1, 2020Jan. 1, 2021. Published July 2020January 2021. Originally approved in 2020. Last previous edition approved in 2020 as D8326 - 20.
DOI: 10.1520/D8326-20.10.1520/D8326-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8326 − 21
adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project’s
many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through
the ASTM consensus process.
1.7 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.
1.8 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.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D6026 Practice for Using Significant Digits in Geotechnical Data
D8151 Practice for Obtaining Rainfall Runoff from Unvegetated Rolled and Hydraulic Erosion Control Products (RECPs and
HECPs) for Acute Ecotoxicity Testing
3. Terminology
3.1 Definitions:
3.1.1 For definitions of common technical terms used in this standard, refer to Terminology D653.
4. Summary of Practice
4.1 Before the kinetic energy can be measured, the raindrop size and drop height must be determined (Note 1). The fall velocities
are also determined based on the drop height and the diameters as shown in Table A1.1. The fall velocities are either interpolated
or selected directly from the table and then the raindrop diameter versus fall velocity is graphed and fitted with a third degree
(cubic) polynomial regression trend line to obtain the regression equation. The constant values from the regression equation are
used to calculate the ground velocities for each of the average raindrop diameters as measured. Once the ground velocity is
determined, the various kinetic energy values are calculated, including the kinetic energy of the simulated event.
NOTE 1—Subcommittee D18.25 is currently developing a standard method for determining the raindrop size independent of any other type of testing. Until
that standard is approved, Practice D8151 provides the information on how to obtain the raindrop size.
5. Significance and Use
5.1 When a raindrop impacts the surface of a soil, it expends its energy and begins the impact-induced soil erosion process. This
kinetic energy of the raindrop is one factor influencing soil erosion. This practice provides a method to quantify the kinetic energy
produced by rainfall simulators.
5.2 Soil erosion is a concern that affects many industries. The highway and road construction industry is particularly interested
in slope protection. There are many ECP manufacturers that rely on testing of their products using rainfall simulators to meet
certain specifications set forth by different agencies.
5.3 Laboratories that offer testing of ECPs use rainfall simulators. Many laboratories are able to adjust their rainfall simulators,
the drop height of the raindrops, and even the slopes of the test plots they use to model expected, anticipated, or actual field
conditions. The kinetic energy associated with the specific configuration of the simulator should be measured.
5.4 Knowing the kinetic energy for the given simulator configuration will provide a way to set minimum and upper limit values
so that comparisons between laboratories can be made as well as having a way to account for the differences between the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
D8326 − 21
laboratories. If there are minimum and upper limit values and the raindrop size is in the same range between laboratories, the
kinetic energy between the laboratories should be similar. Once the kinetic energy is established for a given rainfall simulator
configuration according to a specific standard, comparisons of the results for those specific standards can be made.
NOTE 2—The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the
equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective
testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable
results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
6. Apparatus
6.1 Raindrop Size—See Practice D8151 for the apparatus needed to measure the raindrop size.
6.2 Measuring Device—A surveyor’s rod, tape measure, or similar with enough length and divisions of 5 mm or better to measure
the rainfall distance (drop height) and the test plot width (cross slope) and length (down slope).
7. Procedure
7.1 Raindrop Size—Determine and record the range of raindrop sizes to the nearest 0.001 mm of the rainfall simulator
configuration used following the procedure in 8.4 of Practice D8151.
7.2 Drop Height—Determine and record the drop height of the raindrops to the nearest 0.1 m of the rainfall simulator configuration
used. For inclined structures, the drop height is taken to be from the rainfall simulator to the lowest point of the incline structure.
7.3 Test Plot Dimensions—Determine and record the width (cross slope) and length (downslope) of the test plot to the nearest 0.1
m. Determine and record the area of the test plot, A , to the nearest 0.1 m .
tp
7.4 Cake Pan Dimensions—Determine and record the width and length of each cake pan used to capture the raindrops to the
nearest 5 mm. Determine and record the area of each cake pan, A , to the nearest 0.001 m . Determine and record the total area
cp
of the cake pans, A , to the nearest 0.001 m .
pan
7.5 Fall Velocity—Determine and record the fall velocities to the nearest 0.01 m/s based on the drop height using raindrop
diameters of 1.25, 2, 3, 4, 5, and 6 mm and Table A1.1 (See Annex A1). Graph the raindrop size (abscissa) versus the fall velocities
(ordinate) and fit a third degree (cubic) polynomial trend line to the data and record the regression equation. Table 1 provides the
cubic regression data for commonly used drop heights. For drop heights not listed in Table 1, refer to Annex A1 for instructions
on obtaining the cubic regression data.
TABLE 1 Cubic Regression Data for Commonly Used Drop
Heights
Drop Height a b c d
A
(m)
2.4 0.0282 -0.4071 2.0914 2.3807
3.4 0.0324 -0.4794 2.5539 2.1783
3.7 0.0320 -0.4803 2.6169 2.1715
4.0 0.0313 -0.4796 2.6731 2.1715
4.3 0.0324 -0.5007 2.8028 2.0595
4.6 0.0343 -0.5310 2.9686 1.9051
6.1 0.0397 -0.6330 3.5798 1.3095
A
The drop height in meters corresponds to the drop height in feet as follows: 2.4
m = 8 ft; 3.4 m = 11 ft; 3.7 m = 12 ft; 4.0 m = 13 ft; 4.3 m = 14 ft, 4.6 m = 15; and
6.1 m = 20 ft. For drop heights greater than 6.1 m, the velocity is considered
terminal.
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