Nineteen major tributaries discharge to the Ohio River (Figure 11-2). The 155,000-square-mile ORSANCO district originates on the western slopes of the Appalachian Mountains, with the Allegheny River flowing into the Ohio River from the northwest and the Monangahela River from the south. The southwestern portion of the district is characterized by rolling hills and wide valleys, and the northwest is level or gently rolling. The elevation of the Ohio's riverbed drops 429 feet from the headwaters to the mouth at the confluence with the Mississippi River, with flow in the drainage basin generally toward the southwest. The ORSANCO district is approximately 700 miles long and has an average width of 220 miles. Rainfall in the basin averages 45 inches, and the average annual discharge of the Ohio River into the Mississippi River
is 258,000 cfs. Variations in rainfall, temperature, vegetation coverage, and snow storage have historically caused wide ranges of runoff and streamflows. Low-flow conditions usually occur in July through November; the monthly average, taken at Louisville, Kentucky, ranges from 33,853 cfs in September to 239,613 cfs in March. Figures 11-3 and 11-4 show summer average flows (July-September) and monthly average flows over the 55-year period from 1940 to 1995.
Canalization of the entire Ohio River and some of its tributaries was achieved by 1929, converting the river into a series of backwater pools. The original system of submergible wicket dams has been almost completely replaced by high-lift permanent dams (Tennant, 1998).
POPULATION, WATER, AND LAND USE TRENDS
The Ohio River basin continues to be one of the most important agricultural and industrial centers of the nation. Population in the ORSANCO district has increased steadily over the past few decades, and use of the water resources has increased with the development of the basin. More than 3,700 municipalities, more than 1,800 industries, and three major cities—Louisville, Cincinnati, and Pittsburgh—depend on
Figure 11-3 Long-term trends in mean, tenth, and ninetieth percentile statistics computed for summer (July-September) streamflow in the Ohio River. (USGS Gage 03294500 at Louisville, Kentucky.) Source: USGS, 1999.
the Ohio River Valley. The Ohio River case study area includes a number of counties identified by the Office of Management and Budget (OMB) as Metropolitan Statistical Areas (MSAs) or Primary Metropolitan Statistical Areas (PMSAs). Table 11-1 lists the MSAs and counties included in this case study. Figure 11-5 presents long-term population trends (1940-1996) for the counties listed in Table 11-1. From 1940
TABLE 11-1 Metropolitan Statistical Areas (MSAs) and Counties in the Ohio River Basin Case Study
Wheeling, WV-OH MSA
Belmont County, OH Marshall County, WV Ohio County, WV
Jefferson County, OH Brooke County, WV
Huntington-Ashland, WV-KY-OH MSA
Boyd County, KY Carter County, KY Greenup County, KY Lawrence County, OH Cabell County, WV Hancock County, WV Wayne County, WV
Cincinnati-Hamilton, OH-KY-IN CMSA
Dearborn County, IN Ohio County, IN Boone County, KY
Source: OMB, 1999.
Campbell County, KY Kenton County, KY Pendleton County, KY Brown County, OH Clermont County, OH Hamilton County, OH Warren County, OH Butler County, OH
Louisville, KY-IN MSA
Clark County, IN Floyd County, IN Harrison County, IN Scott County, IN Bullitt County, KY Jefferson County, KY Oldham County, KY
Evansville-Henderson, IN-KY MSA
Posey County, IN Vanderburgh County, IN Warrick County, IN Henderson County, KY
to 1996, the population in the Ohio River case study area increased by more than 50 percent (Forstall, 1995; USDOC, 1998). Agriculture continues to be the dominant land use in the area, although extensive mining is conducted in the watershed; 70 to 80 percent of the national total amount of bituminous coal and a significant amount of natural gas and oil are present in the basin.
The Ohio River supports navigation, power generation, industrial cooling and processing, warm-water aquatic habitats, public water supplies, and recreation. Because the river serves as a water source to industries, agricultural lands, and more than 3.5 million people, and as a waste receptacle for far larger numbers, the river's environment has been placed in a fragile balance.
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