Saint Johns
Saint Johns is a mapped river in the YearMaps hydrographic index. River courses organise settlement, agriculture and frontier-making more durably than any political boundary, and this reach is indexed against the dams, lakes and cities within its catchment.
- Feature Class
- River
- Coordinates
- 29.07°, -81.37°
About Saint Johns
The St. Johns River (Spanish: Río San Juan) is the longest river in the U.S. state of Florida and its most significant for commercial and recreational use. At 310 miles (500 km) long, it winds through or borders twelve counties, three of which are the state's largest. The drop in elevation from the headwaters to the mouth is less than 30 feet (9 m). Like most Florida waterways, the St. Johns has a very slow flow rate at 0.3 mph (0.13 m/s), and is often described as "lazy". Numerous lakes are formed by the river or flow into it, but as a river its widest point is 3 miles (5 km) across, spanning several miles between Palatka and Jacksonville, the latter being the largest urban area on the river. The narrowest point is in the headwaters, an unnavigable marsh in Indian River County. In all, 3.5 million people live within the various watersheds that feed into the St. Johns River.
With a drainage basin of 8,840 square miles (22,900 km2), the St. Johns is one of the major interior wetlands of Florida. It is separated into three major basins and two associated watersheds for Lake George and the Ocklawaha River, all managed by the St. Johns River Water Management District.
Encyclopedic summary adapted from Wikipedia: St. Johns River (CC BY-SA 4.0).
Saint Johns in Depth
Geography
Starting in Brevard County and meeting the Atlantic Ocean at Duval County, the St. Johns is Florida's primary commercial and recreational waterway. It flows north from its headwaters, originating in the direction of the Lake Wales Ridge, which is only slightly elevated at 30 feet (9.1 m) above sea level. Because of this low elevation drop, the river has a long backwater. It ebbs and flows with tides that pass through the barrier islands and up the channel. Uniquely, it shares the same regional terrain as the parallel Kissimmee River, although the Kissimmee flows south.
The river is separated into three basins and two associated watersheds managed by the St. Johns River Water Management District.
Formation and hydrology
Lying within a coastal plain, the St. Johns River passes through an area that was at one time barrier islands, coastal dunes, and estuary marshes. The Florida Peninsula was created primarily by forces and minerals from the ocean. It lies so low that minor fluctuations in sea levels can have a dramatic effect on its geomorphology. Florida was once part of the supercontinent Gondwana. Lying underneath the visible rock formations is a basement of igneous granite and volcanic composition under a sedimentary layer formed during the Paleozoic era 542 to 251 million years ago. During the Cretaceous period (145 to 66 million years ago), the basement and its sedimentary overlay were further covered by calcium carbonate and formations left by the evaporation of water called evaporites.
Human history
Humans arrived on the Florida Peninsula about 12,000 years ago when the ocean was about 350 feet (110 m) lower than today, and the peninsula was double its current size. These earliest people are called Paleo-Indians. They were primarily hunter–gatherers who followed large game, such as mastodons, horses, camels, and bison. Much of the land was far from water—most fresh water was contained in glaciers and polar ice caps. As a result, Florida was an arid landscape with few trees, dominated by grasslands and scrub vegetation.
Around 9,000 years ago, the climate warmed, melting much of the polar ice caps and many glaciers, creating a wetter environment and submerging half the peninsular shelf.
Sections adapted from Wikipedia: St. Johns River (CC BY-SA 4.0).
Saint Johns: Key Facts
| Length | 499 km |
|---|---|
| Average discharge | 425 m³/s |
| Drainage basin | 22,895 km² |
| Mouth | Atlantic Ocean |
| Drainage system | St. Johns River drainage basin |
| Tributaries | Econlockhatchee River, Ocklawaha River, Wekiva River, Black Creek, Pottsburg Creek, Trout River |
Facts from Wikidata Q1677915 (CC0).
Major River Dossiers
Hand-written studies of the great river systems of history.
Connected Reaches
Nearby watercourses in the same drainage network.
Water Bodies in the Catchment
Settlements Along the Reach
Hydraulic Infrastructure Nearby
Surrounding Terrain
Saint Johns: Quick Answers
- Where is Saint Johns?
- Saint Johns is located in United States, at 29.0692° N, 81.3732° W.
- Are there dams on the Saint Johns?
- No dam on the Saint Johns is recorded in the YearMaps dam index, which covers major structures only.