Hydrography: The scientific description and analysis of the physical conditions, boundaries, flow, and related characteristics of surface waters such as oceans, lakes and rivers. The mapping of bodies of water. (Webster’s II New Riverside University Dictionary)
Starting in 2006, the International Hydrographic Organization has designated June 21st as World Hydrography Day. The purpose of this annual celebration is to publicize the work of hydrographers and the importance of hydrography as well as to increase the awareness about protection of safe navigation and marine life protection. So, it may be appropriate on this day in 2019 to consider the importance of hydrography as it relates to Arkansas.
Hydrography is generally considered to be a coastal science. The initiation of the Science of Hydrography in the US was possibly during 1807 when president Thomas Jefferson signed a mandate ordering a survey of our nations coast. The purpose of this survey was to provide reliable nautical charges to the maritime community for safe passage into American ports and along the US Coastline. The job of completing the survey was given to ‘Survey of the Coast’. The Survey of the Coast is now the Office of Coast Survey in the National Ocean Service of the National Oceanic and Atmospheric Administration, a division of the Department of Commerce. The survey now contains information about over 95,000 miles of US coastline.
With respect to Arkansas however, in-land hydrography is much more important. The history of in-land hydrography is not so complete as that of coastal hydrography. But there are several events that could be considered to be precursors to the science in the Americas.
A starting point might be the exploration and mapping of the Mississippi. Louis Jolliet and Jacques Marquette are credited with being the first non-native people to explore and map the Mississippi. Likely, they did not consider their expedition to be a hydrographic survey, they were more interested in the potential for trade as well as the possibility of saving souls. Actually, Marquette and Jolliet didn’t navigate the entire Mississippi. Their route started at the junction of Lakes Michigan and Huron, went up the Fox river then down the Wisconsin river to a confluence with the Mississippi on the border of Wisconsin and Minnesota. From their they canoed down river to the mouth of the Arkansas. They could determine at that point that the river flowed to the Gulf of Mexico so they turned back at that point. Exploration of the upper Mississippi was left for Henry Schoolcraft’s expedition in 1832. Then in 1861, Andrew Atkinson Humphries, with the US Army Corps of Engineers completed a topographic and hydrographic map of the Mississippi published in “Report upon the Physics and Hydraulics of the Mississippi River.
Prior to Jefferson’s mandate to survey the coast, he had already ordered exploration of inland waterways that drained the Louisiana Purchase. These were the great Voyages of Discovery including Louis and Clark’s expedition on the Missouri, Dunbar and Hunters exploration of the Ouachita, Freeman and Curtis’ expedition on the Read River and Zebulon Pikes trip up the Arkansas, all during the 1804 to 1806 time frame. A few years later, during 1818 Henry Schoolcraft explored the James and White Rivers through Missouri and Arkansas. Thomas Nuttall also explored the Arkansas River during the same time span. Once again, these explorers likely did not consider themselves to be hydrographers, but essentially, they were surveying rivers.
Many other surveyors worked for years to generate maps of our nation’s rivers as well as the topography of the country. Their work was published in the General Land Office (GLO) maps during the early to mid-1800’s. The original GLO maps can still be obtained from the Bureau of Land Management. Those maps can provide countless hours of entertaining map gazing if you are so inclined.
Today the task of hydrography falls primarily to the United States Geologic Survey (USGS). The USGS uses field surveys, remote sensing and geographic information systems to compile maps of our nations rivers as well as the watersheds that are tributary to those rivers. The data on rivers is contained in the National Hydrography Dataset (NHD) available on the agency’s website. In the NHD, stream reaches are given a unique identifier and are linked both to upstream and downstream reaches or other water bodies. The USGS also operates and maintains a series of stream gages and monitoring stations making it possible to develop hydrologic models of stream systems. Water utilities can link hydraulic and water quality models to the NHD to efficiently track the progress of a pollutant from a source down to their intake if necessary.
Watershed delineation is also a function of the USGS. In the US, watersheds are delineated in 7 nested scales designated by numeric descriptors starting with 2 digits at the largest scale down to 12 digits at the smallest scale. These numbers are referred to as the Hydrologic Unit Code (HUC). Two-digit HUC’s referred to as ‘major geographic areas’ are the major river basins such as the upper Mississippi or they may include several rivers draining into a coastal area such as the ‘Texas Gulf Coast’. There are 21 major geographic areas. The Arkansas, White and Red rivers are lumped together into region 11.
The next level in the hydrologic unit map is the ‘subregion’ and is designated by 4 digits. There are 221 subregions. The White river in Arkansas above and including the confluence with the Red River is subregion 1101. The third level is the ‘Accounting Unit’. Accounting units are nestled within or may be equivalent to the subregion. To stay with the example, the White River in Arkansas and Missouri is accounting unit 110100. There are 378 accounting units in the US. Next come ‘Cataloging Units’ designated by 8 digits. As an example, the Buffalo River in Arkansas is cataloging unit 11010005. The cataloging unit is the basic unit used by federal agencies for implementation of targeted conservation programs.
Watersheds are further divided into 10-digit ‘watersheds’ and 12-digit ‘subwatersheds. Some states have completed even smaller 14 and 16-digit HUCs. The HUC provides convenient and consistent watershed delineations. These delineations can be used to target conservation efforts by local state and federal programs. They provide a common language for hydrographers and resource managers.
Hydrographers don’t get a lot of recognition. The work is intense and requires lots of expertise. The results help track flooding, manage pollutants and keep drinking water sources safe. Give a hydrographer a big hug today!