As the first major water project in the United States, the old Erie Canal provides an example of the hydrological and environmental consequences of water development. The available record shows that the project aroused environmental fears that the canal might be impaired by the adverse hydrologic effects of land development induced by the canal. Water requirements proved greater than anticipated, and problems of floods and hydraulic inefficiencies beset navigation throughout its history. The Erie Canal proved the practicality of major hydraulic works to the extent that operations and maintenance could cope with the burdens of deficiencies in design. 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 repay 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 increased 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 of the canal, especially when obstructed by many barges, was inadequate to convey the large volumes of water needed to maintain navigable depths over 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 deforestation on floods, water supply, and erosion. The flow of rivers did not decrease 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