PROBLEMS FROM LAND OCCUPANCY 165 



standing examples. Other streams that are well regulated by 

 ground- water reservoir control are the Peconic River in New 

 York, Maurice River in New Jersey, Mad River in Ohio, 

 Tippecanoe River in Indiana, Muskegon River in Michigan, 

 Fox River in Wisconsin, South Fork of Provo River in Utah, 

 and Warm Creek in California. Some very productive ground- 

 water reservoirs are located within these and other similar 

 drainage basins. The recharge areas of many other ground- 

 water reservoirs, occupying only small parts of drainage basins, 

 are composed of very permeable materials, such as sand and 

 gravel, which have high capacity for infiltration. Overland 

 runoff is unlikely in these materials, and permeability is high 

 enough to permit rapid infiltration and ground-water re- 

 charge. For agricultural use it might be desirable to reduce 

 the permeability in order to hold water within reach of plant 

 roots. 



Man has done little to change the infiltration capacities of 

 the least permeable land surfaces. These are formed by the 

 dense bare rocks of mountainous regions, by impermeable 

 shales, or by clays such as those in the rice-growing areas. 

 Infiltration rates are so low that a large proportion of the 

 precipitation is disposed of by surface runoff and evaporation. 

 Streams draining these impermeable areas are characteris- 

 tically "flashy" and are well typified by the Bayou Nezipique 

 in Louisiana, where storms of moderate intensity may cause 

 sharp increases in stream discharge. In many areas infiltration 

 is impeded by clay pan, hardpan, or caliche at shallow depth 

 below the surface, and the impermeability is thus a product 

 of soil development. Where the underlying rock materials 

 are more permeable than these surficial layers, that is, where 

 impermeable soil covers a ground-water reservoir, the re- 

 charge to the ground-water reservoir is impeded by the soil 

 zone. Increasing the permeability of very tight materials is 

 highly desirable but difficult of achievement. 



The surficial materials in most of the country are mod- 

 erately to slightly permeable. The great soil groups of agri- 



