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Latest Earthquake | Chat Share
As Harvey’s record breaking rainfall and catastrophic flood waters recede in Texas and western Louisiana, U.S. Geological Survey teams are collecting high water marks, monitoring water levels and coastal change, retrieving storm tide sensors and collecting samples for water quality analysis.
How High Did the Water Reach?
Now is when the USGS starts the extensive effort of finding high-water marks. During a flood event, rising waters are loaded with floating debris, seeds and dirt that can stick to buildings, trees, or other structures. Once flood waters recede from their highest peak, the line of debris left behind is a high-water mark and they can indicate to scientists the highest point the flood reached. But, these marks are fragile and easily destroyed – both by people cleaning up and by natural weathering – so collecting them is a time-sensitive effort.
For the next several weeks, dozens of USGS employees will be working from sun up till sundown in Texas to find and catalogue these important high-water marks as fast as possible. The crews will be focusing on areas of interest within southeast Texas.
After most major floods, USGS partners with the Federal Emergency Management Agency, the U.S. Army Corps of Engineers, the National Weather Service, and other agencies to identify high-water marks throughout the affected areas. Depending on where these high-water marks are located, they can be used for a variety of purposes, like improving computer models used for predicting the severity of future floods.
Though high-water marks caused by coastal surge and those caused by inland river flooding are similar to each other they are not the same, and the information USGS collects is used for different purposes. For example, with coastal high-water marks, the data can be fed directly into the National Hurricane Center’s storm surge models to verify how accurate their storm surge predictions were before the storm made landfall. This helps them calibrate their models for improved forecasting accuracy during future storms.
One of the most important uses of high-water-mark data is so FEMA can revise their flood hazard maps. These maps help FEMA identify areas that are likely to experience high water in the event of a flood that has a 1 percent chance of happening in any given year. These floods, often referred to as 100-year floods, are the most common severe inundation events, and serve as the foundation for flood management planning.
Another significant use for these high-water marks is the USGS Flood Inundation Mapping effort. These maps are developed using models that incorporate high-water marks, streamgage and storm surge information. The maps can be used by resource managers to assist in updating building codes, evacuation routes, bridge design, environmental assessments and other community planning efforts.
A view of the storm: Reservoir Webcams and Coastal Change Portal
USGS crews installed webcams at the request of the U.S. Army Corps of Engineers at the outflows of Addicks and Barker reservoirs in Houston, Texas. These webcams helped communicate information about the status of releases from these reservoirs. Images at the Addicks Reservoir camera and Barker Reservoir camera are collected at 5 minute intervals, and an animation of the most recent 25 images is available online.
Prior to Harvey’s landfall, USGS scientists, using state-of-the-art modeling, forecast what coastal changes were likely to occur on the Texas coast. The storm surge was expected to cause erosion on almost all state beaches, with water overtopping and in some cases inundating dunes. Scientists from the USGS National Assessment of Coastal Change Hazards storm team are comparing post-storm imagery to predictions of coastal change made in advance of the storm. Before and after photos highlighting coastal changes will be available on the USGS Coastal Change Hazards Portal in the coming weeks.
Peaks of Record
Flooding from Harvey set a number of records in Texas streams and rivers during the peak period of flooding. About 81 streamgages in east and southeast Texas have recorded water levels at flood stage on 20 rivers, streams and bayous, with preliminary reports showing some rivers have already crested reaching their highest levels.
Immediately after the worst of the storm had passed, USGS hydrologists in Texas and from other parts of the southeast were deployed to verify high river flows and peak stages. The crews are also calibrating and repairing streamgages damaged by the storm to ensure they continue to transmit information in real time to users working to protect lives and property.
USGS provisional data shows record peaks on the following bodies of water:
In Texas, the USGS has almost 800 real-time stream, lake, reservoir, precipitation and groundwater stations. The USGS, in cooperation with state, local and federal agencies, operates a nationwide network of more than 8,200 streamgages on inland rivers and streams. These gauges provide real-time data important to the National Weather Service, FEMA, the U.S. Army Corps of Engineers and other state and local partners involved in issuing flood and evacuation warnings, coordinating emergency responses to communities and operating flood-control reservoirs.
Water Quality Sampling
In response to the high flow conditions that resulted from Harvey, USGS crews are collecting water quality samples as part of ongoing routine studies and monitoring. Samples are being collected at selected sites along the Colorado and Trinity Rivers and Lake Houston. The USGS also continuously monitors sediment and water-quality from selected sites on the Trinity, Colorado, Guadalupe, San Juan and Nueces River basins. Some of these data are available real-time at Texas Real-Time Water Quality. Findings may provide insights on the effects of high-flow conditions on water quality. Crews will be monitoring concentrations and transport to coastal areas of select water-quality constituents that may include nutrients, sediment, carbon, E. coli and pesticides. The types of water-quality constituents measured at each site are determined based on local, state or federal needs. Results will be available in the future at USGS Water Data for the Nation.