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Show PART II PRESEITT STATUS OF IRRIGATION Irrigation developments are of greater magnitude than those for meadow lands along upper reaches of tributary streams as they have wider, more complex drainage problems. Many of the irrigated lands at the lower elevations are naturally well-drained. They occupy favorable topographic positions adjacent to natural drainageways, and the soils have sufficient permeability and depth for adequate removal of surplus water. Existing ground water tables in these lands remain at depths well below critical levels during the irriga- tion season without artificial measures. Drainage problems, however, have developed in some irrigated areas of lower reaches, particularly where there are no natural drainage channels or escarpment outlets to remove ex- cess waste water or where lands with fine-textured soils lie in unfavor- able positions on slopes below coarse-textured higher lands that are being irrigated. In valley bottoms near Price and Castle Dale, Utah, and Grand Junction, Rifle, Delta, Montrose, and Cortez, Colo., the drainage problems are com- plex and often difficult to rectify. Fine-textured, massive soils at vary- ing depths over marine shale or mudstone barrier formations restrict drain- age and leaching of salt. As a result of ground water buildup and salt accumulations, these lands are unproductive without artificial drainage. Many miles of drains have been installed to remove and dispose of waste water, some of which are improperly located and only partially effective. Solution of the drainage problem in the Grand Junction Area requires a com- bination of drains and drainage wells. In areas where a permeable gravel aquifer is confined by fine-textured saline soils, the artesian pressure in the deeper aquifers is relieved more effectively by wells than by con- ventional open or closed drains. Drainage wells in this area have lowered the pressure of the artesian aquifer and allowed conventional drains to operate effectively in lowering the water table and leaching salts. Some previously waterlogged tracts in the vicinity of Montrose and Cortez, Colo., have been reclaimed into productive units and others remain undrained. The impaired drainage results from abrupt changes in land gra- dient and the occurrence of a pronounced thinning and concurrent restricted capacity of the gravel aquifers due to undulating shale bedrock approaching or outcropping the surface. The subsurface materials are normally very permeable and respond well to drainage. Complex drainage problems exist in small, scattered areas on benches and low rolling terrain in Montrose, La Plata, and Montezuma Counties of Colorado. The uneven terrain causes ground water accumulations in topo- graphic lows or at small outcrops on slopes shallow to bedrock. Most of these are localized in nature and generally not susceptible to economic drainage• The bench areas of the Uinta Basin in eastern Utah are remnants of old glacial outwash plains. The soils are usually underlain by deposits of gravel and cobble. Drainage problems have developed where dikes occur 38 |