THE WORLD DELTA DATABASE

THE GRIJALVA DELTA

Delta ID        # 11

LOCATION LAT. 18°47’N, LONG. 92°57’W

The Grijalva River is located in Central America and empties into the Gulf of Mexico. The drainage basin is 134,400 sq km in size and the river runs through the basin for a length of only 82 km. The drainage density of the tributaries within the basin is quite low (Figure 44). Numerous large lakes exists within the headwaters of the river system and an extremely large lake, providing most of the fresh water for the country’s agriculture, is located in the northeast part of the basin (Figure 44). Most of the drainage basin lies within Paleozoic granites, but the central basin is located within relatively soft and easily eroded Jurassic and Cretaceous sediments. The western boundary of the basin is defined by the Chiapas Massif, while the southern basin is defined by the complex Sierra Madre de Chiapas-Peten fold belt. The eastern basin lies within the carbonates of the Yucatan Platform. The western and southern boundary display a large number of earthquake epicenters. Tropical and subtropical moist broadleaf and coniferous forests and the average annual rainfall is exceptionally high, 1,591 mm, with a maximum of 2,801 mm and a minimum of 916 mm. The rainy months are May through October.

The river channel is highly meandering and flows within a well-defined alluvial valley. The average annual discharge is 3,079 cu m/sec with a maximum of 6,286 cu m/sec and a minimum of only 87 cu m/sec during the dry months of November through March. Although sediment load is not available, the unconsolidated sedimentary rocks of the drainage basin yields extremely large amounts of sediment as defined by the sediment plumes seen in many of the satellite images. 11-i01 is a satellite image of the delta and lower part of the alluvial valley. The highly meandering river channel is well defined in the image and enlargement of the images indicate numerous abandoned river channels.

The delta is quite large for such a small river system and covers an area of 3,341 sq km. A former active distributary is shown in the satellite image and is located east of the presently active channel. Although the wave energy of the delta front has not been calculated, it must be quite high as most of the delta plain displays a series of seaward prograding beach ridges. Note the erosion displayed along the eastern edge of the delta plain in the vicinity of the former active river mouth. A considerable amount of erosion as taken place as the truncated beach ridges are quite well-displayed. Coastal lagoons are present all along the coast and lie behind prominent barrier islands or prograded beach-ridge complexes. Because of the large variation in river discharge, floods must frequently top the river bands as crevasse splays and well-defined natural levee ridges are prominent in the satellite images. Tidal range is relatively low and although a few tidal channels are present, most of the vegetation within the delta plain consists of fresh-water reed marshes. Most of the small lakes seen in the image are the result of abandoned distributaries and meander cut-off lakes.