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r I I I I I I I I I 'I I I !I I I I I I I ground cover also are factors which influence erodability and potential sediment loads. In urbanizing area where land development is underway, grading and excava- tion operations can multiply eroded soil quantities and sediment deposits by hun- dreds, or thousands, of times. Non-structural measures can be applied prior to, and during, land development to keep soil erosion and subsequent sedimentation with- in tolerable limits. Structural measures, although they are usually more costly and sometimes produce other unexpected problems, can also be implemented effectively. Local conditions and circumstances will ordinarily favor one approach over another. But, unfortunately, the techniques applied are often selected without evaluation of alternative approaches, and decisions are made in favor of methods that can be adopted expeditiously with little advance planning. Stormwater Pollution and Water Quality. The quality of receiving water bodies is one of the most pressing concerns to people in highly-developed urban and metropolitan areas, especially in places where heavy industry and manufacturing is entrenched. Public officials of urban areas having extensive systems of combined sewers are greatly concerned about water pollution contributions from sewer over- flows and treatment plant by-passes. The demands of the U.S. Environmental Pro- tection Agency, under Section 208 of the 1972 Amendments to the Water Pollution Control Act (P.L.92-500), have required public officials in metropolitan areas to develop areawide plans for controlling and eliminating pollution from stormwater. Non-structural measures (land use controls, improved street cleaning, regular re- moval of accumulated sediment, source control of pollutants, etc.) are usually applicable more quickly, economically, and with less adverse secondary impact than are structural methods. The latter may involve massive sewer separation projects or construction of enlarged treatment facilities, huge reservoirs and other single- purpose public works. Groundwater Supplies. Protection and conservation of groundwater supplies is a major concern of people in many urban areas that depend upon underground sources for municipal water supply. In such places, today, the possible entry of pollutants transported by and stored in surface runoff is an important factor in- volved in all decisions regarding local activities. Although little information was available years ago concerning the characteristics of runoff and its pollution potentials, studies conducted in recent years prove the need for quality control of stormwater. Also of concern is the maintaining of a "sufficient" underground water supply at all times. Any actions or events that may threaten available quan- tities are factors demanding attention. Man's land development activities that cause increases in runoff flows can produce interruptions of, and a lessening of, the natural process of groundwater recharge. Uncontrolled land development, com- bined with increased groundwater withdrawal, can produce continual, serious lower- ing of the natural groundwater table, particularly during periods of drought. As a result, the water supply available for consumption by humans, animals, trees and other flora and fauna is often insufficient. This may require importation of pot- able water from other sources. Survey of Stormwater Management Agencies As a mjans of developing a broad perspective of stormwater management agencies, a survey(a was made in 1975 of 56 public agencies located in various parts of the United States. Included were: public works and planning departments of local a. Poertner, H. G.: Survey of participants in seminars on urban stormwater management, in Atlanta and Denver, sponsored by the U.S. Environmental Protection Agency (unpublished). 37