Welcome to Hydro-Blog of Sophal Try: 2016

Thursday, December 29, 2016

Universal Soil Loss Equation (USLE)

The Universal Soil Loss Equation (USLE) predicts the long-term average annual rate of erosion on a field slope based on rainfall pattern, soil type, topography, crop system and management practices. USLE only predicts the amount of soil loss that results from sheet or rill erosion on a single slope and does not account for additional soil losses that might occur from gully, wind or tillage erosion. This erosion model was created for use in selected cropping and management systems, but is also applicable to non-agricultural conditions such as construction sites. The USLE can be used to compare soil losses from a particular field with a specific crop and management system to "tolerable soil loss" rates. Alternative management and crop systems may also be evaluated to determine the adequacy of conservation measures in farm planning.

The USLE model comprises five parameters: rainfall erosivity factor, soil erodibility factor, slope length factor, slope gradient factor, vegetation cover and management factor, and support practice management factor. The accuracy of USLE estimation is dependent on the spatial resolution of the input data. The USLE model is expressed by Equation:

A = R x K x LS x C x P

þ A represents the potential long-term average annual soil loss in tonnes per hectare (tons per acre) per year. This is the amount, which is compared to the "tolerable soil loss" limits.

þ R is the rainfall and runoff factor by geographic location. The greater the intensity and duration of the rain storm, the higher the erosion potential. R factor can be calculated by the formula of Lo et al. (1985) for application:

R = 38.46+3.489P

where R is the annual mean rainfall erosivity (N h^-1 yr^-1) and P is the average annual precipitation (cm).

This equation is generalized by Kenneth & Jeremy (1994). After changing the unit of mean annual precipitation to mm yr-1 and the unit of R by multiplying by 10 to obtain SI units (MJ mm ha-1 h-1yr-1), Eq. (2) is simplified as follows:

R = 38.46+0.35P

where R is the rainfall erosivity (10 MJ mm ha-1 h-1yr-1) and P is the mean annual precipitation (mm yr-1). This equation is considered an appropriate estimator of rainfall erosion in tropical or subtropical climate regions (Eiumnoh, 2000).

þ K is the soil erodibility factor. It is the average soil loss in tonnes/hectare (tons/acre) for a particular soil in cultivated, continuous fallow with an arbitrarily selected slope length of 22.13 m (72.6 ft) and slope steepness of 9%. K is a measure of the susceptibility of soil particles to detachment and transport by rainfall and runoff. Texture is the principal factor affecting K, but structure, organic matter and permeability also contribute.

þ LS is the slope length-gradient factor. The LS factor gives the effects of topography, such as the length and steepness of slopes, which are closely related to the amount of soil erosion. It has been shown that the steeper slope is, the higher the velocity of overland flow, which increases soil loss. is used to calculate the LS factor (Mitasova & Mitas, 1999) :

where LS is the slope-length and steepness factor (no unit), θ is the slope angle (degree), Flow Accumulation is used to integrate flow direction in the calculated LS, and Cellsize is the DEM resolution. The following picture is an example of Annual Average Precipitation and DEM in Mekong River Basin.

þ C is the crop/vegetation and management factor. It is used to determine the relative effectiveness of soil and crop management systems in terms of preventing soil loss. The C factor is a ratio comparing the soil loss from land under a specific crop and management system to the corresponding loss from continuously fallow and tilled land. The C factor resulting from this calculation is a generalized C factor value for a specific crop that does not account for crop rotations or climate and annual rainfall distribution for the different agricultural regions of the country. This generalized C factor, however, provides relative numbers for the different cropping and tillage systems, thereby helping you weigh the merits of each system.

þ P is the support practice factor. It reflects the effects of practices that will reduce the amount and rate of the water runoff and thus reduce the amount of erosion. The P factor represents the ratio of soil loss by a support practice to that of straight-row farming up and down the slope. The most commonly used supporting cropland practices are cross-slope cultivation, contour farming and strip cropping

Support Practice	P Factor
Up & down slope	1.0
Cross slope	0.75
Contour farming	0.50
Strip cropping, cross slope	0.37
Strip cropping, contour	0.25

This figure shows an example of result of soil erosion in Mekong River Basin.

The result mentioned that the 3S sub-basin has high soil erosion risk.

by Sophal Try
Please visit our Facebook page: Water Resources and Disaster Management
Credit to Hoang Thu Thuy for figures in case study of Mekong River Basin

Reference:

Eiumnoh, A (2000), “Integration of Geographic Information Systems (GIS) and Satellite Remote Sensing (SRS) for Watershed Management”, Technical Bulletin 150. Food & Fertilizer Technology Center, Taiwan.

FAO Proceedings of the validation forum on the Global Cassava development strategy (2000). “Strategic environmental assessment : An assessment of the impact of cassava production and processing on the environment and biodiversity”, Vol. 5, Food and Agriculture Organization of United Nations, International Fund for Agriculture Development.

Kenneth G. Renard, and Jeremy R. Freimund (1994). “Using Monthly Precipitation Data to Estimate the R-Factor in the Revised USLE”, Journal of Hydrology, Vol.157, pp. 287-306.

Lo A, El-Swaify S.A, Dangler E.W, and Shinshiro L (1985). “Effectiveness of Ei30 as an Erosivity Index in Hawaii”, Soil Erosion and Conservation, El-Swaify S.A., Moldenhauer W.C. & Lo A. (eds), Soil Conservation Society of America, Ankeny, Iowa, pp. 384-392.

Mitasova,H and Mitas.L (1999). “Modeling Soil Detachment with Rusle 3d Using GIS”, University of Illinois at Urbana-Champaign

Wednesday, May 11, 2016

GIS, RS & GPS

Geographic Information System (GIS)

Geographic Information System (GIS) is a computer-based information system that enables storage, management, capture, modeling, manipulation, retrieval, analysis and representation of geographically referenced data. GIS Technologies provide help in organizing huge databases in structure format. GIS allows the viewing and analysis of multiple layers of spatially related information associated with a geographic region/location.

GIS has been used in Environmental application, for example, Best Management Practices (BMPs) for Non-Point Source Pollution Control, Storm Water Management, Watershed Management, Spill Control Planning and Response, Hazardous Material Management, Air Pollution Management and Planning, Wetlands Delineation, Forestry Management, Mining and Geologic Resource Management, and Wildlife Habitat Management.

Remote Sensing (RS)

Remote Sensing is the science of obtaining information about objects or area from a distance without physical contact, typically from aircraft or satellite.
Remote Sensing is useful for generating environmental indicators with multi-resolution, multi-scale, multi-spectral, quick appropriate method, unbiased mapping and monitoring of natural resources both in space and time domain. RS provides timely and accurate information on spatial distribution of Land Use, Soil, Elevation, Precipitation, Vegetation, Forest, Geology, Water Resources, and other useful parameters.
RS addresses the impacts of natural resources and socio-economic aspects before, during, end, and post development projects, for example, Hydropower dam constructions.
RS has been used as indicators for natural resources impact parameters such as Surface Runoff, Water Resource Development, Groundwater level/yield, Variety of Irrigated Area, Crop Diversity, Crop yield, Crop intensity, Fodder availability, Afforestation, Deforestation, Climate Change, Biodiversity, Land Use Change, Socio-Economic, and Migration Status.

Global Positioning System (GPS)

GPS Technology has provided an indispensable tool for management of agriculture and natural resources. GPS is a satellite and ground-based radio navigation and locational system that enables the user to determine very accurate locations on the surface of the earth. Simple and Inexpensive GPS units are available with accuracies of 3 to 20 meters, and some more sophisticated precision agricultural systems can obtain centimeter level accuracies.

Application of GIS, GPS and RS

The usage of GIS, GPS, and RS technologies, either individually or combination, span a broad range of applications and degrees of complexity. Simple applications might involve determining the location of sampling sites, plotting maps for use in field, or examining the distribution of soil types in relation to yields and productivity, for example. More complex applications take advantage of the analytical capabilities of GIS and RS software including vegetation classification for predicting crop yield or environmental impacts, modeling of surface water drainage patterns, or tracking animal migration patterns.

Reference

Milla, K. A., Lorenzo, A., & Brown, C. (2005). GIS, GPS, and remote sensing technologies in extension services: Where to start, what to know. Journal of extension, 43(3).

Bhunia, G. S., Dikhit, M. R., Kesari, S., Sahoo, G. C., & Das, P. (2011). Role of remote sensing, geographic bioinformatics system and bioinformatics in kala-azar epidemiology. Journal of biomedical research, 25(6), 373-384.

by Sophal Try
Please visit our Facebook page: Water Resources and Disaster Management

Tuesday, April 5, 2016

Cherry Blossom 2016

Wednesday, March 30, 2016

What Is El Niño?

El Niño (Spanish word for male child) is a naturally occurring event in the equatorial region which causes temporary changes in the world climate. El Niño refers to a whole complex of Pacific Ocean sea-surface temperature changes and global weather events. The ocean warming off South America is just one of these events. Every three to seven years, an El Niño event may happen during many months to more than one year causing economic and atmospheric worldwide. The worst El Niño occurred in 1997-1998.
In contrast, La Niña (Spanish word for female child) refers to an anomaly of unusually cold sea surface temperatures found in the eastern tropical Pacific. La Niña occurs roughly half as often as El Niño.

Wednesday, March 16, 2016

Integrated Water Resources Management in Cambodia (IWRM)

Integrated Water Resources Management is a step-by-step process of managing water resources in a harmonious and environmentally sustainable way by gradually uniting stakeholders and involving them in planning and decision-making processes, while accounting for evolving social demands due to such changes as population growth, rising demand for environmental conservation, changes in perspectives of the cultural and economic value of water, and climate change (Stakhiv, 2009).

Water is a limited resource that is essential for economic growth and environmental and social well-being. Because it affects everyone, managing this precious resource requires balancing the interests of the many different user groups and individuals. Without that balance many conflicts can occur. Promoting coordinated water resources management in a basin that open to all stakeholders will not only resolve such conflicts but will also bring enormous benefits to society, the basin, and to individual stakeholders.

Integrated Water Resources Management has been identified as one of the basic water resources related policy approaches in several recent important commitments and recommendations (Varis et al., 2006). IWRM aims at developing democratic governance and promote balanced development in poverty reduction, social equity, economic growth and environmental sustainability. IWRM is a theoretical concept with not much sound scientific background from real-life development projects and not much sustainable impact on the environment, society and economy.

The facets of IWRM (Varis et al., 2006)

The Tonle Sap Lake is one of the world's most productive large lacustrine-wetland eco-system, with an extreme biodiversity. For many of the Mekong fish species, the floodplain of the lake, and particularly the riparian flooded forest and shrublands. The lake also operates as a natural flood water reservoir for the lower Mekong Basin in the wet season and make an important contribution to the dry season flow to the Mekong Delta in Vietnam.

Referemces:

STAKHIV, E. Z. (2009). IWRM Guidelines at River Basin Level. World.

Varis, O., Kummu, M., Keskinen, M., Sarkkula, J., Koponen,J., Heinonen, U., andMakkonen, K. (2006). Integratedwater resources management on the Tonle Sap Lake, Cambodia. Water Scienceand Technology: Water Supply, 6(5),51-58.