| Popis: |
Highways may have favorable or unfavorable influences on our environment. These may be social, economical, or physical, chemical, and biological. The presence or absence of deep cuts and extensive fills can produce a large variety of transformations on the terrain and in the hydrogeologic environment. Such possible changes include: (1) the beheading of aquifers when present in soils and shallow bedrock (2) the development of extensive ground-water drains where cuts extend below the water table (3) damage and pollution of water supplies (4) changes in ground- and surface-water divides and basin areas (5) reduction of induced streambed infiltration rates due to sedimentation (6) siltation of channels causing flooding, erosion, and reduction in recharge areas on flood plains (7) obstruction of ground-water flow by abutments, retaining walls, and sheet pilings, and (8) changes in runoff and recharge characteristics. Unstable slopes may result by piping failures where cuts serve as ground-water drains, thus changing the seepage forces which may act outward or upward and either increase driving moments or reduce resisting moments. Water quality changes may result from: (1) sediment damage to surface and ground-water supplies (2) pollution, resulting from use of highways and related accumulations of oils, chemicals, and hazardous substances through accidental spills, and (3) road side litter and debris. Changes occur by economic activity stimulated by the highway. Sanitary, industrial and solid wastes may be disposed of in an unsatisfactory manner. Pollution may result from maintenance procedures used to control weeds, insects, snow and ice, and from exposed stock piles of chemicals used for these purposes. Acid and other chemically polluted waters may be produced where road cuts and fills expose pyrite-bearing strata which normally cause serious mine drainage problems. |
