Geology Reports⌕ Search
Home/Archive/USGS

USGS · sir20145227

Hydrographic survey of Chaktomuk, the confluence of the Mekong, Tonlé Sap, and Bassac Rivers near Phnom Penh, Cambodia, 2012

Benjamin J. Dietsch·Brenda K. Densmore·Richard C. Wilson
View original source ↗Read source document ↗Export metadata ↓

Abstract

The U.S. Geological Survey, in cooperation with the U.S. Department of State, Mekong River Commission, Phnom Penh Autonomous Port, and the Cambodian Ministry of Water Resources and Meteorology, completed a hydrographic survey of Chaktomuk, which is the confluence of the Mekong, Tonlé Sap (also spelled Tônlé Sab), and Bassac Rivers near Phnom Penh, Cambodia. The hydrographic survey used a high-resolution multibeam echosounder mapping system to map the riverbed during April 21–May 2, 2012. The multibeam echosounder mapping system was made up of several components: A RESON Seabat™ 7125 multibeam echosounder, an inertial measurement unit and navigation unit, data collection computers, and a Real-Time Kinematic (RTK) Global Navigation Satellite System (GNSS) base station. The survey area was divided into six survey subreaches and each subreach was surveyed within 3 days along survey lines oriented parallel to the flow direction. Complete coverage of the riverbed was the operational objective; however, to obtain broad spatial coverage, gaps between parallel swaths were permitted, especially in wide, shallow areas where multibeam swath widths were narrow. The survey was referenced to two existing bench marks with known geographic coordinates by establishing a GNSS base station on the bench marks each day and using real-time corrections from the base station to correct boat navigation data. The World Geodetic System of 1984 (WGS 84) ellipsoid was used during data collection to reference height, and data were adjusted to the local datum, Ha Tien 1960, during postprocessing. The quality of hydrographic surveys was described by an uncertainty estimate called total propagated uncertainty (TPU). Calculations of TPU were completed for the hydrographic survey data resulting in the maximum TPU of 0.33 meters. The mean and median TPUs were 0.18 meters, and 99.9 percent of TPU values were less than 0.25 meters. Detailed hydrographic maps of Mekong, Tonlé Sap, and Bassac Rivers showing the riverbed elevations surveyed April 21–May 2, 2012, referenced to Ha Tien 1960 were produced. The surveyed area included a 2-km stretch of the Mekong River between the confluence with the Tonlé Sap and Bassac Rivers, and extended 4 km upstream and 3.6 km downstream from the 2,000-m confluence stretch of the Mekong River. In addition, 0.7 km of the Bassac River downstream and 3.5 km of the Tonlé Sap River (from the confluence to Chroy Changvar Bridge) upstream from their confluence with the Mekong River were surveyed. Riverbed features (such as dunes, shoals, and the effects of sediment mining, which were observed during data collection) are visible on the hydrographic maps. All surveys were completed at low annual water levels as referenced to nearby Mekong River Commission streamflow-gaging stations. Riverbed elevations surveyed ranged from 24.08 m below to 1.54 m above Ha Tien 1960.

Explore related subjects

Scientific Investigations ReportReport
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 10.914224006944366° to 13.036669323115246° latitude; 103.64501953125° to 105.8148193359375° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Benjamin J. Dietsch, Brenda K. Densmore, Richard C. Wilson. 2014. Hydrographic survey of Chaktomuk, the confluence of the Mekong, Tonlé Sap, and Bassac Rivers near Phnom Penh, Cambodia, 2012. https://doi.org/10.3133/sir20145227

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Baseline water-quality inventory and summary for the Paterson Great Falls National Historical Park, New Jersey

The Paterson Great Falls National Historical Park (PAGR), established in 2011 in the City of Paterson, New Jersey, contains many cultural, historical, and natural resources. Because of the PAGR’s young age and limited resources, a long record of natural resource data is not available for use to guide future park management and planning decisions. A detailed natural resource inventory was identified as an immediate need in the “Foundation Document—Paterson Great Falls National Historical Park,” given the history of extensive industrial activity throughout the PAGR and the Passaic River Basin. The U.S. Geological Survey, in cooperation with the National Park Service and the Urban Waters Federal Partnership for the Lower Passaic River, inventoried water-quality monitoring efforts and compiled historical water-quality data from secondary data sources to define baseline conditions in the PAGR and the surrounding study area. This report documents the methods used to harmonize water-quality data aggregated from multiple sources for the PAGR study area. Procedures implemented during data harmonization include compiling data from multiple sources, assessing the dataset for completeness, addressing metadata concerns, and creating a consistent and quality-assured dataset for future analysis. The harmonized dataset contains 14 aggregated surface-water sites, 1,103 individual sampling days, and 32,000 water-quality records throughout the period of record defined for this study (1952–2021). Summary statistics and comparison to water-quality criteria are provided for focus parameters that can support PAGR management, including field properties, suspended material, total dissolved solids, specific conductance, chloride, sulfate, Escherichia coli, nutrients, contaminants of concern related to fish consumption advisories, and litter and floatable debris. A spatial data gap was identified for the recreational area near the base of the Great Falls and immediately downstream from a known combined sewer overflow discharge location. Analytic data gaps were identified for continuous streamflow and water-quality parameters, floatable debris characterization, and harmful algal blooms identification. Continuous collection of contaminants of concern was identified as a temporal data gap, as these parameters were not consistently collected within the study area. The water-quality data synthesis and summary presented in this report can assist PAGR staff in understanding the complex baseline water resources within the study area and can serve as a baseline to design future water-quality monitoring efforts and evaluate changes in water quality over time. The harmonized dataset, as well as future New Jersey Department of Environmental Protection and New Jersey Harbor Discharge Group monitoring data and assessments, can also be used to examine the status and trends in surface-water quality, support compliance with the Clean Water Act (33 U.S.C. 1251 et seq.), and further investigate changes to park water resources that can affect ecological and human health.

New Jersey↗
USGS2026

Slip tendency and dilation tendency of Quaternary faults in the Great Basin region, Arizona, California, Idaho, Nevada, Oregon, Utah, and Wyoming

This report presents the results of slip tendency and dilation tendency analysis of Quaternary faults in the Great Basin region, in the states of Arizona, California, Idaho, Nevada, Oregon, Utah, and Wyoming. This effort was undertaken as part of two studies: the U.S. Department of Energy Geothermal Technologies Office-funded Innovative Geothermal Exploration through Novel Investigations of Undiscovered Systems (INGENIOUS) project, which is a multidisciplinary, multi-institution effort to develop new methodologies and best practices to accelerate the discovery of new, commercially viable hydrothermal resources; and the U.S. Geological Survey Geothermal Resources Investigations Project. The goal of this work is to identify faults and fault segments that are appropriately oriented to be stress-loaded for slip or to dilate under the ambient stress conditions. Both conditions may make such faults more likely to host permeability and fluid flow relative to other faults in the region. Slip tendency and dilation tendency were calculated for all fault segments in the study area from the U.S. Geological Survey Quaternary Fault and Fold Database. Results demonstrate that faults with high slip tendency and dilation tendency are common in the Great Basin region. The areas containing many high slip tendency and dilation tendency fault segments are associated with high strain rates. These areas also host a relatively high proportion of the known hydrothermal systems. This indicates that faults with high slip tendency and dilation tendency in areas with high strain-rate are potentially most prospective for hosting hydrothermal systems. The database published in coordination with this report contains the slip tendency and dilation tendency results data, including the fault geometry and stress data used to calculate these quantities, for both the Great Basin study area and the smaller INGENIOUS study area.

Arizona, California, Idaho, Nevada, Oregon, Utah, ↗
USGS2026

A spatial analysis of the groundwater emergence flood hazard in Long Island, New York, and coastal areas surrounding Long Island Sound in New York, Connecticut, and Rhode Island

Long Island, New York, and nearby coastal areas surrounding Long Island Sound are densely populated and, like other coastal areas, are susceptible to flooding from several potential sources, including stormwater from precipitation events, tidal flooding and storm surge, and groundwater emergence flooding. Groundwater emergence fooding refers to the intersection of a rising water table with land surface or critical infrastructure. Many studies of flood drivers either neglect or only briefly discuss how shallow groundwater conditions may contribute to or exacerbate flood conditions. As a part of a comprehensive study of compound flood hazards in the coastal areas of Long Island and Long Island Sound, a spatial analysis was completed by the U.S. Geological Survey, in cooperation with the Environmental Protection Agency’s Long Island Sound Partnership, formerly called the Long Island Sound Study, using available regional datasets to characterize the potential hazard for groundwater emergence flooding. The approximately 3,100 square mile study area was subdivided into 11,407 grid cells that were 900 meters by 900 meters (approximately 3,000 feet by 3,000 feet), for the purpose of integrating the spatial datasets to calculate and map the groundwater emergence flood hazard. The depth to the water table, hydrologic soil groups, and National Land Cover Database were harmonized to the common grid. A groundwater emergence flood hazard score was calculated for each grid cell for current average conditions following a set of rules accounting for the depth to the water table and the percentage of area within each cell with slow infiltrating soils. A scenario with a higher sea-level position was also calculated for the Long Island part of the study area. The calculated groundwater emergence flood hazard score was reviewed in conjunction with the National Land Cover Database to identify developed areas and associated infrastructure that may be at risk of potential groundwater emergence flooding. Study results indicate that the groundwater emergence flood hazard is highest in coastal areas and near surface water where the water table is close to ground surface. Inland areas away from surface waterbodies are not likely to be exposed to groundwater emergence flooding. For Long Island, in the scenario with higher sea-level position, a greater groundwater emergence flood hazard is calculated for some locations closer to the coast and where land is submerged. Away from the coast and surface-water drainage, the groundwater emergence flood hazard is similar between the current average sea-level condition and the higher sea-level position scenario.

Connecticut, New York, Rhode Island↗