SUMMARY STATEMENT WAS) 
do not always coincide with periods of need for water. Many 
streams carry objectionable quantities of sediment. Moreover, 
the normal regime of flow can be altered and its sediment load 
greatly increased by unwise use of the watershed lands. 
Inasmuch as most of the comments about inflowing water came 
out of the discussion, rather than from the papers, I would like 
to develop this aspect of the subject a little more fully. 
Dams and reservoirs are a well-known means of regulating the 
availability of water from streams. They do not, however, control 
water on the land or maintain the soil in place on watershed 
slopes. The greatest threats to the usefulness of streamflow as a 
source of water for arid lands are sedimentation in downstream 
water storage structures and floods. The control of these menaces 
and the increasing of water yields pose many problems in the field 
of upstream watershed management. Among them are: 
1. Inadequate understanding of the source of sediment and of 
soil formation and erosion processes. 
2. The necessity of distinguishing between normal and accel- 
erated erosion, for which adequate criteria have not been devel- 
oped in many places. 
3. The need for controlling accelerated erosion on slopes and in 
channels for which effective measures are not yet known in many 
places. 
4. Prevention of watershed deterioration under the impact of 
increasing demands for use of the timber and forage resources, 
for which guides are also lacking. 
5. Inadequate information about the quantitative effects of 
watershed treatments on sediment production and streamflow 
characteristics. 
