USGS Hydrologic Data Collection Program in North Carolina
USGS North Carolina Data Chief, Jeanne Robbins, provides an overview on hydrologic data collection techniques for North Carolina.
The following podcast is a product of the U.S. Geological Survey and the North Carolina Water Science Center.
[Intro audio]: Hydrologic data delivery mix... Jeanne Robbins: "Quite often you will see a reporter standing next to a USGS stream gage during a flood, but you never really hear that that is indeed what it is, a USGS stream gaging station."
In this age where cell phones and shifting weather patterns are common place a group of highly skilled USGS scientists have given those silent sentinelles a voice of their own. Using cell phones to alert you when your drive at five should detour low lying areas...or when that rafting trip (text-message alert) might be a little short on white water
Today on Water Science for a changing world USGS NC Water Data where it's been, and where it's going. I am Ray Douglas your guide and this is Water Science for a changing world."
Douglas: Joining us is Jeanne Robbins USGS Data Chief for the North Carolina Water Science Center. Jeanne thanks for talking with us today.
Robbins: Ray I am delighted to be here. I appreciate the opportunity to talk with you today about the USGS Hydrologic Data Collection Program and specifically the program in North Carolina. You know it's the mission of the USGS to provide reliable, impartial, timely information that is needed to understand the Nation’s water resources.
Douglas: Well, the USGS has certainly been the collector and keeper of our Nation's water data, but how does the North Carolina program fit into that history?
Robbins: We have a very long history of hydrologic data collection within the USGS and in North Carolina and our program has benefitted from the partnerships that we have with other federal, state and local agencies that assist in funding this data collection effort through our Cooperative Water Program. In fact we have a stream gage in NC that actually dates back to 1895. If this gage could talk, I can only imagine the stories it would tell.
Douglas: Well we can get into talking gages a little later, but what type of history has this particular gage seen?
Robbins: During its 114 years, this gage has seen some dramatic floods and droughts and in fact, just last year we recorded the lowest ever streamflow at the site of 170 cubic feet per second that would be equivalent to about 1270 gallons every second. And while this seems like a lot of water, when you consider that this area drains a watershed of almost 1000 square miles, that’s really not much water.
Douglas: 1000 square miles, what is the largest flood ever recorded at that gage?
Robbins: The largest flood recorded at this gage was one of the most devastating floods in Western North Carolina, the flood of 1916 and the peak streamflow during this event was 110, 000 cubic feet per second and a river stage of 23 feet. And it’s important to note that while the streamgages directly monitor and record river stage, it is streamflow or the volume of water passing by the gage that is critical to defining the 1% flood and subsequently the 1% floodplain.
Douglas: Another critical component to mention is the USGS staff that visit these gages during floods and droughts and all of the other conditions in between recording streamflow measurement to calibrate the gages.
Robbins: It's that streamflow more so than river stage that is also critical for use in sizing road culverts and designing bridges and determining the amount of water that can safely be withdrawn from a river or the amount which is critical for the support of the aquatic ecosystem. And needless to say both river stage and streamflow information from our gages are closely monitored by recreational users and quite often I will get a telephone call from a canoer or a fisherman that is letting me know that a streamflow gage might not be operational, and that we need to get the information out there to them as well.
Douglas: Well this season seemed light with fewer hurricanes to contend with I am sure that was much appreciated.
Robbins: Well sometimes it seems like we have had more than our share of floods in North Carolina. In the last 15 years we have witnessed the 1 percent flood or what we used to call the 100-year flood in most of the river basins in North Carolina, the major river basins. We have gotten away from the term 100-year flood because it gives the impression that once you have a 100-year flood you can sit back and relax for the next 99 years, but what it really means is that you have a 1 in 100 chance of this type of flood happening in any given year. So even if you had a 100-year or what we term the 1% chance flood this year, the chance of it happening next year is still 1 in 100.
And this also goes to why it is important to collect streamflow data for long periods of time to gain more confidence in our ability to define the 1% chance flood. We need at least 10 years of data to even begin to compute flood frequency statistics and our confidence in these estimates is improved with longer periods of data collection. Many of these large floods in North Carolina were the result of rainfall from tropical systems that either made landfall along the coast of North Carolina or along the gulf in something that we like to call back door systems that then traveled up through central or western North Carolina.
Douglas: Jeanne how does the stream gaging program in North Carolina differ from other states?
Robbins: Well that's one of the unique things about the USGS hydrologic data collection program and our stream gaging program particularly is that we use a national set of standards and all of our streamgages are part of the National Streamflow Information Program. We use pretty much the same techniques to measure streamflow in North Carolina as well as North Dakota, although it may be colder in North Dakota. Most all of the streamgaging stations across the country are now what we call real-time and transmit data either via satellite or some other type of telemetry back to USGS offices for display on our web pages. In fact during the coming year we have a national effort to upgrade those gages currently equipped with satellite telemetry to ensure that they transmit no less frequently than every hour. This means that data on our web pages should never be more than 1 hour old.
Douglas: Can you tell us a little about the groundwater program in North Carolina?
Robbins: In addition to our basic streamflow data collection program which dates back over 100 years we maintain important networks for the collection of groundwater level information and water quality information too. The groundwater component is an important element of the overall hydrologic cycle and needs to be measured and monitored too. Some of the oldest wells in our network are relatively shallow wells representative of climatic effects on groundwater conditions. A nearby well at Chapel Hill, NC dates back to 1943 and one in the mountains of western North Carolina in Haywood County dates back to 1955. It is critical to monitor this component of the overall hydrologic cycle as groundwater provides the base flow to streams throughout the year and these data are especially important in assessing drought conditions, as we witnessed during the exceptional drought that we had in NC from 1998 – 2002. It's also important because 52% of North Carolina's population depends upon groundwater for its drinking water supply and 2.7 million North Carolina residents use privately owned private domestic wells. So our long term goal is to have at least one observation well in each of the 100 counties in North Carolina to evaluate the effects of impending and persistent drought conditions.
Douglas: And a big public concern, water quality and it's data collection in your program.
Robbins: Our water quality data collection network includes sites that continuously monitor key water quality components like dissolved oxygen, pH, temperature and specific conductance and sites where we routinely collect water samples and analyze for particular constituents like nutrients (including nitrogen and phosphorous), suspended sediment, metals, chlorophyll, pesticides and a host of other pollutants. It is unfortunate that during these trying economic times we have lost financial support for some of our long-term continuous water quality monitors in the Pamlico and Neuse River estuaries. These were valuable for explaining conditions related to fish kills, such as the extensive one that occurred in the Neuse River this past September. All of this information is critical to USGS meeting our mission and to water resource and emergency managers… not to mention recreational users that really value the data as well.
Douglas: So Jeanne, what would you say is the most significant change over the past 100 years in streamflow data collection?
Robbins: While some of our streamflow data collection activities have changed very little in the last 100 years some things have changed dramatically, like our ability to transmit data via satellite near real time and over UHF and VHF radio frequencies. We now display all of our real-time data on the internet for anyone to view and use. And these data are critical to emergency managers during floods, to National Weather Service Flood Forecasters and to water resource managers responsible for water supplies across the state and the country, not to mention the public who also rely on these data.
Douglas: But what is the most significant change that you can cite?
Robbins: Probably the single greatest change in streamflow measurement technology during the last 100 years has been the development and application of acoustic instruments for measuring streamflow. This technology is rapidly replacing traditional mechanical current meters for streamflow measurement that have been around since the early days of our data collection activities. These devices are known as Acoustic Doppler Current Profilers and they use sound to measure water velocity using a phenomenon known as the Doppler effect. You have probably experienced that yourself Ray if you have listened to the sound of a train or car horn as it seems to change frequency as it passes by. This has allowed us to make more accurate streamflow measurements in a fraction of the time that we used to, and has permitted us to measure streamflow in tidal rivers and is being investigated for use in measuring suspended sediment concentration in streams too.
Douglas: O.K. we have a good overview of the water program in North Carolina. Now I understand that you have a program that you have been working on for quite some time and you are quite excited about it. If you could tell us about North Carolina HAS.
Robbins: This is really one of the most exciting new features of our data collection program in North Carolina the North Carolina Hydrologic Alert System, otherwise know as NC HAS. It was developed as a prototype sort of proof-of-concept notification system to provide real-time email or text message notifications on river stage, streamflow and rainfall conditions.
The North Carolina Hydrologic Alert System, is a customizable system that provides these notifications when a user-specified threshold is met at USGS data-collection sites in North Carolina. These notifications can be set for when the river stage or streamflow either exceeds or falls below a user-specified threshold at any site of their choice. Likewise, these notifications can be established at rainfall sites for cumulative 1-, 2-, 4-, 6-, or 12-hour rainfall amounts.
You can really easily subscribe via a simple web interface for either hourly or daily alerts. The site selection is accomplished either through a clickable map or simply by entering the USGS station number into a selection box. You can set up notifications for any number of sites and each one comes with a link to the recent real-time data for the site and a link that will allow you to unsubscribe to the alert.
Douglas: Finally a good use for text-messaging. This sounds like it something that would be very useful for emergency managers and recreationalists users too. What about sites outside of North Carolina, what's happening there?
Robbins: Well I am glad you asked Ray because NC-HAS is still in development and its very much in its infancy but we are working to make it a robust national application within about 6 months. We are currently beta testing the system, and encouraging users to test the application and to provide us with any feedback you have through the feedback link on the NC-HAS web page, So be on the lookout for USGS-HAS in the very near future.
Douglas: O.K Jeanne well give us that link where we can all go and subscribe and start receiving Hydrologic Alert text-messaging from USGS.
Robbins: You can find the alert system at nc.water.usgs.gov/alert/
Douglas: Jeanne thanks for talking with us today.
Robbins: Well Ray I am always glad to talk about our Hydrologic data collection network. USGS is really a hidden gem within the Department of the Interior.
[Close Audio]: USGS Hydrologic Alert simulation audio mix...
Water Science for a changing world is a product of the U.S. Geological Survey and the North Carolina Water Science Center.