Symposium Statement


Soil Erosion Research for the 21st Century

Honolulu, Hawaii; 3-5 January, 2001



This consensus document was developed by participants of the symposium "Soil Erosion Research for the 21st Century", sponsored by the American Society of Agricultural Engineers (ASAE) and thirteen other professional societies and agencies[1].  Participants comprised 210 soil erosion researchers and field practitioners from 30 countries, who gathered with the specific purpose of reviewing current scientific understanding of soil erosion and sedimentation and setting research directions and goals for the next two decades.  This document represents the views of those esteemed individuals and is not necessarily a position of ASAE as a whole.


It is the considered consensus of this group that:


1) Soil erosion is a complex process encompassing detachment, transport, and deposition, and is caused by wind, water, and physical disturbance.  Soil erosion reduces land productivity, challenges agricultural sustainability, and degrades soil, air, and water quality.  Indirectly, soil erosion also degrades environmental quality through contaminants attached to the sediment.  Soil erosion also interacts strongly with the global carbon cycle and climate change processes.  In some conditions, these impacts are so severe that they reduce the quality of life and economic well-being, and they can even threaten survival in poorer nations.


2) Research into the detachment, transport, and deposition of soil must be a high priority in order to better define these processes and their potential consequences.  With this information, better control methods can be developed and implemented.


3) Soil erosion research must rapidly evolve and develop improved strategies to respond to the new and increasing demands of erosion assessment and resource conservation.  High-priority examples include strategies for monitoring erosion as it varies in time and space, along with assessment of off-site impacts.


4) There must be an effort to increase the awareness of policy makers and the general public of the impact of erosion and sediment transport on overall environmental quality.  The importance of continued support for efforts to assess these impacts and to protect the environment must be emphasized.


5) Substantial progress has been made over the past 50 years in understanding erosion and sediment transport and their effect on the environment.  This understanding has led to the development and adoption of a wide variety of erosion control practices, but problems caused by erosion and sediment continue and much remains to be accomplished.  Increased awareness of erosion impacts on air and water quality and on global climate change raises new challenges for erosion researchers.


The Symposium participants discussed the issues and challenges facing erosion researchers over the next 5-20 years in three general areas:  Wind Erosion, Water Erosion, and Quantification of Erosion.  A brief listing of the issues and suggested tasks in addressing each are included below.  The issues and responses most frequently raised were:


1) Long-term and large-scale coordinated erosion monitoring and broad data collection is critical, since it allows researchers to better ascertain the impacts of land management policies and practices on erosion, delivery, and the resulting degradation of soil, air, and water resources.  These efforts must more fully reflect the spatial and temporal scale of erosion and its impacts, and the topographic complexity of the processes.


2) We need greater interdisciplinary efforts in developing erosion prediction and control technology, and for ensuring better adoption of those technologies at the local level.  Land managers and end users must be more involved in the entire process in order to increase the rate of adoption.


3) We need to more effectively collect erosion data in a more organized and useful manner.  We must then also develop tools to allow for more effective sharing of that information.


4) We need to continue work on understanding the fundamental processes involved in both erosion and sediment transport by water, wind, and physical disturbance, and in how best to model those phenomena.  Though our understanding has increased greatly over the past decades, there are still some substantial gaps, including such processes as streambank and gully erosion, transport and deposition processes, effects of sediment on biotic integrity, the role of dust in climate change, etc.


5) We must greatly increase our understanding of the transport of sediment by wind or water, and the off-site impacts of this sediment on air and water quality.


It is the considered consensus of the participants at this symposium that successfully addressing these issues will result in a greater understanding of erosion and sediment transport processes, leading to improved erosion control practices and better tools for land-use planners.  This will ultimately result in more effective and efficient protection of the soil, air, and water resources.








The American Society of Agricultural Engineers is a professional and technical organization dedicated to the advancement of engineering applicable to agricultural, food, and biological systems.  Founded in 1907, ASAE comprises 9,000 members representing more than 90 countries.  ASAE members serve in industry, academia, and public service and are uniquely qualified to determine and develop more efficient and environmentally sensitive methods of cultivating food and fiber for an ever-increasing world population.



Results of Symposium Discussions


It was the major goal of the International Symposium on Soil Erosion Research for the 21st Century to encourage discussion of the challenges and issues facing soil erosion research, in order to achieve greater understanding and to move towards a common vision.  Opportunities for discussion included panel sessions, small-group discussions, and informal rap sessions.  These sessions were divided into the three general categories of Wind Erosion Research, Water Erosion Research, and Erosion Quantification.  What follows is a summary of the issues of greatest importance in each of the three general categories.



Wind Erosion Research



Issue 1: We need better physically-based equations to describe the entrainment, transport, and deposition of soil by wind at various scales.


- jeopardizes our understanding, prediction, and subsequent interpretation of the erosion processes

- undermines the credibility and usefulness of erosion research

- limits the application of the models

- undermines attempts to deal with the issues of off-site impact and land management decisions because the rates of erosion, transport, and deposition are fundamental to those issues

- leads to inaccurate models and poor conservation planning decisions

Required Actions:

- establish multi-disciplinary research teams

- encourage increased fundamental research to better define the critical parameters and to verify the resulting equations

- develop, select, and properly use more effective data-collection equipment and techniques




Issue 2: We do not have adequate tools to assess the environmental impact of land management decisions.


- makes it difficult to convince the community, policy makers, and land managers that changes are necessary and worth pursuing

- limits research into the role of dust in climate change in spite of its obvious importance

- keeps land managers from carrying out appropriate cost-benefit analyses

- makes it impossible to properly assess the sustainability of current or proposed management practices

- makes it difficult to adequately assess the impacts of proposed policy changes

Required Actions:

- develop regional models by integrating existing wind erosion models and decision-support tools

- develop additional alternative management practices to minimize erosion

- improve understanding of the impacts of erosion on fertility

- develop techniques to more effectively transfer the technology to the end users




Issue 3: We have a poor understanding of off-site wind erosion impacts on the environment and its inhabitants.


- results in targeting incorrect causal factors and in setting inappropriate legislative or regulatory goals

- results in poor predictions of air quality impacts and sedimentation problems caused by wind erosion

- makes it difficult to test environmental targets since the level of impact is unknown

- keeps us from understanding the impact on global climate change

- limits our ability to assess the economic impacts of erosion

Required Actions:

- develop models of dust deposition and dispersion

- study the impact of dust on high-priority issues such as air quality and human health

- undertake economic analyses of the off-site impacts

- develop methods to monitor dust emission, transport, and deposition

- develop indirect methods (e.g., remote sensing) to track off-site movement





Issue 4: Our technology transfer efforts are weak and ineffective.


- hinders adoption of alternative management practices

- makes it difficult to ensure that practices are used correctly

Required Actions:

- form interdisciplinary links between all stakeholders

- involve all stakeholder groups throughout the effort

- provide informational / educational materials to schools, clubs, etc.




Issue 5: Our methods of monitoring and assessing the spatial and temporal variation in wind erosion are inadequate.


- makes it very difficult and expensive to collect good data

- makes it difficult to quantify variability of erosion and the impact of that on decision-making

- means that we are often forced to use information collected at another scale

- results in great uncertainty in making planning recommendations

Required Actions:

- resolve scale impacts on erosion and transport

- develop standardized methods for a series of measurement techniques

- develop reliable and standardized indirect measurement methods as surrogates for direct methods

- develop easier, more accurate, and less-expensive ways of ground-truthing remotely-sensed information

- develop interdisciplinary teams to research and develop indirect methods






Water Erosion Research


Issue 1: We have an inadequate understanding of basic erosion processes, especially those related to irrigation, tile drainage, rangelands, water quality, gullies, deposition, and erosion caused by soil disturbance processes such as tillage.


- weakens credibility with model users when their cases are not represented in the models

- limits the usability of the models in conditions not intensively studied

- results in poor model estimates and perhaps in poor conservation planning decisions

- limits flexibility in the use of erosion models

Required Actions:

- develop fundamental research programs in these areas

- integrate research by various scientists in different locations




Issue 2: Conservation practices have not been widely adopted at farm and local levels


- results in poor utilization of research resources

- weakens efforts to protect local, national, and global soil/water/air resources

Required Actions:

- develop and document improved soil conservation practices

- develop a much better understanding of the factors controlling adoption/rejection of the practices at farm and local levels




Issue 3:  We have an incomplete and limited data set describing erosion and sediment delivery.


- results in data biased towards specific situations (mineral soils, agricultural lands, moderate slopes, and temperate climates)

- limits expansion of erosion prediction and control to other regions and land uses

- hinders understanding of sediment delivery because data sets often do not include critical parameters

- limits our understanding of long-term changes and effects

- results in duplication of data collection efforts

- limits understanding of fundamental erosion/delivery processes

Required Actions:

- develop and maintain long-term comprehensive monitoring programs, including all the factors associated with the entire erosion/delivery system

- set up systems specifically to collect information on the erosion and off-site impacts of extreme events

- develop international standards for data sets that will be useful across the broadest range of environments



Issue 4: We have a very poor understanding of how best to approach modeling erosion, sediment yield, and related water quality impacts.


- results in models often more complex than can be justified by the supporting data

- results in poor modeling of two-dimensional and long-term phenomena

- weakens our modeling of the consequences of erosion (e.g., soil quality and productivity changes, the sustainability of management systems, water quality impacts)

- makes it more difficult to integrate socio-economic factors in our models

- results in poor representation of basic erosion processes, field conditions and associated variability, and topographic complexities

- makes our models very weak in predicting sediment delivery and off-site impacts

- results in models generally based on what we know and can measure rather than on what is really important

Required Actions:

- continue fundamental research in how to most efficiently use available information in building models

- develop fundamental new approaches to estimating sediment delivery in complex situations

- begin multi-disciplinary work on defining the appropriate degree of complexity for these models

- develop better measures of spatial and temporal variability of critical parameters

- compile and strengthen information on the soil quality and water quality impacts of erosion and sediment delivery

- compile socio-economic data related to soil erosion and sediment movement, and integrate these data into assessment models



Issue 5: We have generally not given enough attention to assessing the impacts and consequences of erosion and resulting sediment transport


- means that though we may have a good estimate of how much soil is eroded, we know less about how much is transported off-site, and even less about the implications of that transport

- makes it very difficult to use our results for good cost/risk/benefit analyses

Required Actions:

- reassess the whole concept of soil loss tolerance

- examine how upland erosion impacts the TMDL of streams, reservoirs, wetlands, coastal zones, and off-coast impacts such as on the Great Barrier Reef and hypoxia in the Gulf of Mexico

- develop long-term field studies specifically looking at on- and off-site impacts, rather than just erosion rates

- develop better uses of erosion information and expertise in addressing critical water quality issues





Issue 6: Our integration of research efforts and results in the wider context has been relatively weak.


- results in poor integration across spatial scales, which requires linking lab- and plot-scale research studies with watershed-scale management practices

- results in poor integration with the efforts of social scientists and economists, and even with physical scientists with different approaches to the problem (e.g., fluvial geomorphologists)

- results in poor integration of erosion and sediment transport by water with other land degradation processes (e.g., changes in soil structure, deforestation, salinization, tillage erosion)

- results in poor integration of end user into our efforts, yielding poor adoption rates

Required Actions:

- develop more interdisciplinary research efforts

- share data openly, and standardize its collection and storage



Issue 7: We do not always understand the large-scale implications of the phenomena we study on the small scale.


- yields an inadequate understanding of the impacts of erosion and sediment transport on global climate change, such as impacts on carbon sequestration

- results in a poor understanding of erosion and sediment transport by scientists in other disciplines

Required Actions:

- develop a sound conceptual understanding of the potential role of erosion and sediment transport on these phenomena

- collect data to assess these impacts and to incorporate the results into useful models




Erosion Quantification



Issue 1: We have seen poor adoption of conservation strategies at larger scales (watersheds, regions, etc.), sometimes because of our inability to show the impacts of those strategies.


- results in a perception that we cannot provide large-scale answers and proof that conservation strategies work at those scales

- means that we get a poor return on scientific investment if we don’t get adequate adoption, resulting in less policy support

Required Actions:

- involve end users in all stages of tool development and implementation

- develop technologies that are profitable, cheap, environmentally friendly, and easy to implement

- develop watershed planning documents using multiple strategies to resolve erosion problems

- integrate physical and social science models to develop acceptable techniques

- determine the needs and priorities of users

- emphasize research that will support the decisions of aid policy makers to encourage adoption of conservation systems



Issue 2: In our data-collection efforts, we may not fully understand what is being measured and its variability.


- results in measurement techniques that often affect the parameter being measured, skewing the data

- means that we don’t adequately measure the spatial and temporal variability of the parameter

- means that in sharing the data, we often do not include information critical to assessing its usefulness

- weakens our cost/risk/benefit analyses due to a poor understanding of the data variability

Required Actions:

- evaluate existing measurement techniques and resulting data

- develop new techniques to measure parameters with minimal or well-known impacts

- develop measurement technique standards, including Quality Control/Quality Assurance methods

- develop reporting standards that include spatial and temporal variability and the setting of the measurement



Issue 3:  We lack a comprehensive database to allow us to efficiently use data collected by others.


- makes it far more difficult to do any large-scale or global erosion assessment, or to track trends in air, water, or soil quality

- deprives modelers of data that may be useful for verification/validation

Required Actions:

- establish an organization to build and maintain a meta-database (i.e., a catalog of what data are available, under what conditions they were collected, etc.)

- assess and catalog existing data

- periodically evaluate usefulness of the database



Issue 4:  We have a poor understanding of how spatial and temporal variability in soil properties, surface conditions, and climate impact soil erosion.


- results in poor erosion predictions and resulting decisions, since erosion often occurs only under certain combinations of conditions and we do not adequately understand the variability in those conditions

Required Actions:

- continue long-term plot studies under a much wider range of conditions

- develop cheaper data-collection methods to allow for more replicates

- do a better job of incorporating variability into erosion prediction models

- develop a better conceptual understanding of the sources of the variability

- develop models assessing the long-term impacts of soil erosion on soil variability and soil quality



Issue 5:  We need to better understand the risks of long-term soil erosion on soil, air and water resources.


- results in inadequate cost/risk/benefit analyses

Required Actions:

- carry out a better compilation and analysis of historical data, and how best to use those records

- develop better projection tools for time-varying phenomena, including feedback mechanisms to show how current erosion will affect future erosion, etc.

- encourage collection of the representative data most useful in making these projections                



Issue 6:  We generally do a much better job of estimating erosion on a hillslope than of modeling or quantifying sediment delivery from the source to some destination of concern.


- results in poor water-quality models

- results in poor sediment-delivery measurements

- yields a poor understanding of the pathways taken by the sediment and of its residence time within the area of interest

Required Actions:

- educate policy makers and regulators on the importance of good sediment delivery quantification in meeting environmental standards, such as NPDES or TMDL limits

- establish an interdisciplinary team to develop a comprehensive research strategy

- identify pathways and mechanisms of sediment movement

- determine the impact of temporal and spatial scales on these pathways and mechanisms


[1]Co-sponsors were: American Society of Agronomy (ASA), Chinese Soil and Water Conservation Society (CSWCS) Taiwan, Council of Agriculture (COA) Taiwan, European Society for Soil Conservation (ESSC), International Erosion Control Association (IECA), International Union of Soil Sciences (IUSS), Soil Science Society of America (SSSA), Soil and Water Conservation Society (SWCS), USDA-Agricultural Research Service (ARS), USDA-Cooperative State Research, Education, and Extension Service (CSREES), USDA-Forest Service (FS), USDA-Natural Resources Conservation Service (NRCS), and World Association of Soil and Water Conservation (WASWC).