The weight of prior experience that upland streams, such as the Potomac and Mohawk Rivers, had proved unsatisfactory for dependable navigation, led to a decision to build an independent canal which freed the location from the constraints of river channels and made possible a cross-country water route directly to Lake Erie.
The decision on dimensioning the canal prism - chiefly width and depth - involved balance between a fear of building too small and thus not achieving the economic potentials, and a fear of building too expensively. The constraints proved effective, and for the first part of its history the revenues collected were sufficient to replay all costs. So great was the economic advantage of the canal that the rising trend in traffic soon induced an enlargement of the canal cross section, based upon a new but riskier objective build as large as the projected trend in toll revenues would finance. The in-creased revenues did not materialize.
Water supplies were a primary concern for both the planners and the operators of the canal. Water required for lockage, although the most obvious to the planners, proved to be a relatively minor item compared with the amounts of water that were required to compensate for leakage through the bed and banks of the canal. Leakage amounted to about 8 inches of depth per day. The total quantities of water taken into the canal made it the largest hydraulic undertaking of the 19th century in the United States. The diversion of water to factories that were attracted to the canal as a source of hydraulic power added to the water requirements. Although new feeders and reservoirs to extend the supply were built throughout the canal's history, these efforts to cope with water shortages were never fully successful. The primary cause of the persistent deficiencies in supply was the method used to estimate the available flow of the streams during extended dry spells. Ad hoc, spot measurements of streamflow consistently led to overestimation of the dependable supply.
There was a persistent hydraulic problem as well. The cross section the canal, especially when obstructed by many barges, was inadequate convey the large volumes of water needed to maintain navigable depths of the long distances between feeders.
The major flood problem was caused by cross-drainage-the small creeks that crossed under the canal in culverts. Washout of culverts was a never ending source of sporadic disruption of traffic of 1 or 2 weeks duration. Repairs and replacements could not cope with the problem created by deficiency in information about the flood potentials of the small streams.
A fortunate occurrence of severe floods in 1817 at the start of canal construction. Provided such clear and persuasive evidence of the flood potentials of the Mohawk River, which the canal followed for about 110 miles, so as to compel putting the canal at a high level in difficult terrain.
Environmental anxieties, broached early in the planning of the canal, centered on the potentially adverse effects of land development and deforesta-tion on floods, water supply, and erosion. The flow of rivers did not de-crease as originally feared. Land use did not increase - the intensity of flooding and so endanger the canal. Viewed first as a conveyor of pure water from Lake Erie to the State, water in the canal became polluted by the wastes from the persons and animals involved in operations. The extent of pollution, however, was within the oxygen assimilation capacity of the water and the canal did not become septic. The canal contained fish life, but its role in the migration of the troublesome sea lamprey and alewife to the Great Lakes remains unclear.
Among the large set of effects of the canal upon the water environment that took place but that had not been considered in the planning or design were those on river flows, landforms, ground water, vegetation, and fish mi-gration. The overriding fact that the initial anxieties of the planners proved unwarranted and that environmental conditions did not become intolerable by the standards of that time probably led to neglect of consideration of environmental risks in subsequent public works practice during the 19th century.