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Houston, the most populous city in theSouthern United States, is located along the upperTexas Gulf Coast, approximately 50 miles (80 km) northwest of theGulf of Mexico atGalveston. The city, which is theninth-largest in the United States by area, covers 601.7 square miles (1,558 km2), of which 579.4 square miles (1,501 km2), or 96.3%, is land and 22.3 square miles (58 km2), or 3.7%, is water.[1]
Houston is located in theGulf Coastal Plainbiome, and its vegetation is classified as temperate grassland. Much of the city was built onmarshes,forested land,swamp, orprairie, all of which can still be seen in surrounding areas.
The city's topography is very flat, makingflooding a recurring problem for its residents. The city stands about 50 feet (15 m) above sea level—the highest area within city limits being 90 feet (27 m).[2] However,subsidence, caused by extensivegroundwater pumping and resource extraction, has caused the elevation to drop 10 feet (3.0 m) or more in certain areas. As a result, the city turned tosurface water sources for its municipal supply, creating reservoirs such asLake Houston andLake Conroe (of which Houston owns two-thirds interest).
Houston has four majorbayous passing through the city:Buffalo Bayou, which runs into downtown and theHouston Ship Channel; and three of its tributaries:Brays Bayou, which runs along theTexas Medical Center;White Oak Bayou, which runs through the Heights and near the northwest area; andSims Bayou, which runs through the south of Houston and downtown Houston. The ship channel goes pastGalveston and into theGulf of Mexico.
Houston is located 165 miles (266 km) east ofAustin,[3] 112 miles (180 km) west of theLouisiana border, and 250 miles (400 km) south ofDallas.[4]Houston County, Texas, located 100 miles (160 km) north of Houston, is unrelated to Houston.
Houston is largely located within the Northern Humid Gulf Coast Prairieslevel IV ecoregion (34a), a subset of theWestern Gulf coastal grasslands level III region as defined by theUnited States Environmental Protection Agency. This region is generally underlaid byQuaternary-aged sand, silts, and clays (clay,clay loam, or sandy clay loam) and covered bygrasslands with occasional clusters ofoak trees.[5]
The land surface in and around the city of Houston is composed of alternating layers of red, gray, sandy brown, and black organicclay; thesestrata generally dip to the southeast at a slope of 0.06% (3 feet (0.91 m) of vertical change for every 1 mile (1.6 km) of distance traveled).[6] These soils weredeposited bytributaries of local waterways, particularly theBrazos andTrinity rivers.[6] There is a considerable contrast in soil composition to the north aroundCypress Creek; most of the surface there consists of tan-colored sand with small amounts of gray clay.[6] The north and northwestern regions of Houston and Harris County feature a slightly steeper slope than other parts of the city, with occasionalescarpments caused byfaulting orerosion.[6]
Thesedimentary layers underneath Houston ultimately extend down some 60,000 feet (18,000 m), with the oldest beds deposited during theCretaceous.[7] Between 30,000 feet (9,100 m) and 40,000 feet (12,000 m) below the surface is a layer ofsalt, the primary source ofsalt domes that dot the metropolitan area.[7] Since salt is morebuoyant than other sediments, it rises to the surface, creating domes andanticlines and causingsubsidence due to its removal from its original strata.[7] These structures manage to capture oil and gas as it percolates through the subsurface;Pierce Junction is a notable example of a heavily drilled salt dome oil field in Houston.[8]
The Houston region is generallyearthquake-free, despite the presence of 86 mapped and historically active surfacefaults with an aggregate length of 149 miles (240 km).[9] This includes theLong Point–Eureka Heights fault system which runs through the center of the city. No significant historically recorded earthquakes have occurred in Houston, but researchers[who?] do not discount the possibility of such quakes having occurred in the deeper past, or occurring in the future.
Land subsidence has occurred across Greater Houston, primarily due to the pumping of water from subsurface aquifers (seeGroundwater section). This subsidence may also be associated withslip along the faults; however, the slippage is slow and not considered an earthquake, in which stationary faults must slip suddenly enough to create seismic waves.[10] The clay below the surface precludes the buildup of friction that produces ground shaking in earthquakes. As a result, faults generally move at a smooth rate in what is termedfault creep.[citation needed] The recently built Premium Outlet Mall and newly renovated US 290 have experienced the slippage of the Hockley Fault, which was redefined as being farther east than previously mapped.[11]
Houston, often popularly referred to as theBayou City,[12] is crossed by a number ofslow-moving, swampy rivers, which are essential to draining the region's broadfloodplains. The city was founded at the convergence ofBuffalo Bayou andWhite Oak Bayou, a point today known asAllen's Landing.
Buffalo Bayou is the longest and largest of the bayous which flow through Houston, following a 53-mile (85 km)[13] route fromKaty throughMemorial,Rice Military,Downtown, theEast End,Denver Harbor, andChannelview before meeting theSan Jacinto River atGalveston Bay. The broad eastern stretch of the river, known as theHouston Ship Channel, plays an essential role in thePort of Houston and is home to one of the largestpetrochemical refining complexes in the United States.[14] Buffalo Bayou's environs are also home to significant amounts of parkland, includinglinear parks such asTerry Hershey Park and Buffalo Bayou Park which serve as corridors for walking and bicycling.
White Oak Bayou, a majortributary of the Buffalo, has its source inJersey Village and travels 25 miles (40 km)[15] southeast, throughInwood Forest,Oak Forest, andHouston Heights.Brays Bayou, another major tributary to the south, originates nearMission Bend and travels 31 miles (50 km)[16] throughAlief,Sharpstown,Meyerland,Braeswood Place, theTexas Medical Center,Riverside Terrace, and the East End before meeting Buffalo Bayou atHarrisburg.
Two more significant tributaries of Buffalo Bayou flow through parts of Houston outside the Interstate 610 loop. Greens Bayou, which originates in far northwest Houston nearWillowbrook, flows for 43 miles (69 km)[17] throughGreenspoint and undeveloped areas of northeastern Harris County. Sims Bayou, which has its source nearMissouri City southwest of Houston, flows for 23 miles (37 km)[18] pastAlmeda,Sunnyside,South Park, andManchester.
Houston's topography is further defined by a large number of creeks andditches. Overall, this intricate system of waterways is essential toflood control; Houston is well known as one of the most flood-prone cities in the United States.[19] Since the mid-20th century, theUnited States Army Corps of Engineers, in cooperation with the city andHarris County Flood Control District, haschannelized, paved, widened, and deepened extensive sections of all of the five major bayous specified above, with the notable exception of some parts of the Buffalo near Memorial. The Buffalo Bayou watershed also features twoflood controlreservoirs,Addicks Reservoir andBarker Reservoir, which retain large amounts of water after extreme rainfall events.
Cypress Creek drains a significant portion of northern Harris County. The river flows for 52 miles (84 km)[20] through the suburban areas ofCypress andSpring before joining the San Jacinto River. The creek's watershed, which covers 310 square miles (800 km2), is one of the largest in the county.[20]
TheBrazos River straddles some of Houston's extreme western and southwestern suburbs, particularlySugar Land andRosenberg.
Houston contains few naturally formed lakes.Lake Houston, an 11,854-acre (4,797-hectare) reservoir located approximately 15 miles (24 km) northeast of Downtown, was created by damming the San Jacinto River in the 1950s to create a dependable, long-term supply ofdrinking water.[21] The lake is owned and operated by the City of Houston.[22] Besides supplying water to the city, the lake is also a central feature of theKingwood community and serves as a recreational destination.
Galveston Bay is a central feature of theGreater Houston metropolitan area. The bay serves an essential economic role as the home of the Houston Ship Channel and a large fishing industry and is also an important destination for recreation and coastal wildlife. Covering approximately 600 square miles (1,600 km2), theestuary extends 30 miles (48 km) inland from the coast and has a maximum width of 17 miles (27 km).[23] Important regional communities, includingGalveston andTexas City, are located along the bay. While the City of Houston proper does not adjoin the bay, its limits do extend southward to encompass theNASAJohnson Space Center and the community ofClear Lake.[24]
Clear Lake, which gives the aforementioned community its name, is atidal lake[25] withbrackish water located on the western side of Galveston Bay. Covering about 2,000 acres (810 hectares), the lake is fed byClear Creek and inflow from the bay.[25] Ultimately, the Clear Creek watershed covers an area of 250 square miles (650 km2) encompassing seventeen tributaries.[25]
Twofreshwater aquifers, the Chicot and Evangeline, underlie the Greater Houston area. These aquifers are composed mostly of sand and clay. The Chicot is located above the Evangeline, and aconfining layer separates them from the Jasper aquifer below, which is mostly saltwater.[26] A majority of drinking water supply wells in Houston are drilled to depths between 1,000 feet (300 m) and 2,000 feet (610 m).[26]
Extraction of water, oil, and gas from these aquifers has causedland subsidence throughout the Greater Houston region since the early 20th century. Before 1942, Houston's municipal water supply was sourced exclusively from groundwater wells.[26] The inception of thepetroleum industry at the beginning of the century also led to widespread resource extraction around the city.[26] Surface elevations began to drop with thewater table, and by the 1970s, areas around the Houston Ship Channel had subsided up to 7 feet (2.1 m) due to rapid industrialization, prompting the creation of the Harris–Galveston Coastal Subsidence District.[26] By the end of the decade, subsidence had intensified to 10 feet (3.0 m) in some parts of east Houston, and 3,200 square miles (8,300 km2) of the region had experienced at least 1 foot (0.30 m) of sinking.[26]
The creation of the district, which enforced a transition from ground to surface water consumption, effectively halted subsidence in the most severe areas near the Ship Channel; aquifer recharge has helped water table elevations return to normal.[26] However, in the northwestern region of the city, groundwater levels – and, concurrently, land surface elevations – continue to decline.[26]
When Houston was established in 1837, the city's founders—John Kirby Allen andAugustus Chapman Allen—divided it into political geographic districts called "wards." The ward designation is the progenitor of the current-day Houston City Council districts—there are nine in all.
Locations in Houston are generally classified as either being inside or outsideInterstate 610, known as the "610 Loop" or simply "The Loop". Inside the loop generally encompasses the central business district, and has come to define an urbanlifestyle and state of mind. Elizabeth Long, the author of the 2003 bookBook Clubs: Women and the Uses of Reading in Everyday Life, wrote that most of the upper middle classes in the 610 Loop live in the southwestern part of the inner city in the areas nearHermann Park, theHouston Museum District,Rice University, and theTexas Medical Center, while some portions of northern Houston and Eastern Houston have been gentrified and also have upper middle classes.[27]
The outlying areas of Houston, the airports, and the city's suburbs and enclaves are outside the Loop. Another ring road,Beltway 8 (also known simply as the "Beltway" or as the "Sam Houston Tollway"), encircles the city another 5 miles (8 km) farther out. Parts of Beltway 8 are toll roads, but for most of the route, motorists can drive in the adjacent "feeder" or service roads at no charge.[citation needed]Farm to Market Road 1960 (FM 1960) forms a semicircle in northern Houston and is another dividing line.[28] The third ring road,State Highway 99 (also known as the Grand Parkway), is under construction.[citation needed] Long stated that most of the wealthier Houston suburbs are west and north of the central city, while to the southeast theClear Lake/NASA "[represents] another burgeoning concentration of largely aerospace-related prosperity".[28]
Houston, being the largest city in the United States without zoning laws, has grown in an unusual manner. Rather than a single "downtown" as the center of the city's employment, five additionalbusiness districts have grown throughout the inner city—they areUptown,Texas Medical Center,Greenway Plaza,Westchase, andGreenspoint. If these business districts were combined, they would form the third-largest downtown in the United States. The city also has the third-largestskyline in the country (after New York City and Chicago), but because it is spread over a few miles, pictures of the city show—for the most part—the main downtown area.[citation needed] The growth of the Greater Houston area has occurred from all directions from the city core.[29]
