PART VII — WATER RESOURCES, FORESTRY, AND AGRICULTURE 



gradualness. But the geologic 

 processes that shape the steep 

 lands are often violent and er- 

 ratic. Landslides, avalanches, 

 massive floods, and abrupt 

 changes in stream cutting and 

 deposit are normal incidents in 

 the down-wearing of steep 

 mountain slopes. Since hazard 

 is often unsuspected and fre- 

 quency is on a larger scale 

 than laymen reckon with, such 

 events often appear as "ac- 



cidents" or are attributed to 

 the wrong causes. 



It is clear that man's activities in 

 some susceptible landscapes decades 

 and centuries ago have increased the 

 frequency or severity of such events 

 and triggered self-accelerating erosion 

 of unstable slopes. Now, landslides 

 and slips associated with road con- 

 struction are a continuing problem 

 as roads are extended into steep 

 remote areas. Hence, there is need 



for much better understanding of 

 soil and geomorphic processes on 

 vulnerable steep lands with a view 

 to characterizing hazards and devis- 

 ing measures of avoidance or control. 

 Such research concerns not only 

 forest management operations but 

 equally highway construction, ski- 

 slope developments, powerline clear- 

 ance, mining, and all other activities 

 that change stream courses, slope 

 loading, or the stabilizing effects of 

 vegetation. 



Factors Relating Forest Management to Water Quality 



Water derived from forested wa- 

 tersheds is generally the highest- 

 quality water found under natural 

 conditions although, contrary to pop- 

 ular opinion, water from pristine 

 forest streams is frequently unsafe 

 for human consumption. Under nat- 

 ural conditions, water quality is a 

 function of: 



Geology and Geochemistry — Par- 

 ent materials and the products of 

 their weathering influence mineral 

 content. 



Topography — Elevation, exposure, 

 and steepness influence the form of 

 precipitation, time and mode of de- 

 livery, evaporation rates, water tem- 

 perature, infiltration opportunity. 



Climate — Climate influences or 

 determines the amount and form of 

 precipitation input and the time and 

 mode of delivery of water; indirectly, 

 it influences sediment and organic 

 content, rate of weathering, soil de- 

 velopment, and vegetative cover. 



Soils — Type and depth of soil 

 mantle are significant factors in wa- 

 ter quality determination, especially 

 in surface water. They influence the 

 rate and amount of infiltration and 

 percolation and, consequently, quality 

 and amount of groundwater recharge, 

 the rate and amount of erosion, and, 

 thus, the sediment and chemical con- 

 tent of surface water. Soil influences 



biological activity and nutrient cy- 

 cling processes and is a determining 

 factor in type and density of vegeta- 

 tive cover. 



Biota — Includes animal and plant 

 forms. Animals, from soil bacteria 

 and microorganisms to large wild- 

 life forms, play a significant role in 

 determining water quality. Similarly, 

 vegetative forms from lowly mosses 

 through forests exert an influence on 

 water quality. These combined in- 

 fluences include bacteria, nutrients, 

 organic matter, and sediment or tur- 

 bidity content, hydrogen ion activity, 

 suspended solids, and water tempera- 

 ture. 



Natural Disturbances — Natural ca- 

 tastrophes including forest fires, in- 

 sect and disease depradation, earth- 

 quakes, volcanic eruptions, landslides, 

 avalanches, hurricanes, and tornadoes 

 all influence water quality, often in a 

 major way. 



The Role of Forests 



Forest vegetation influences and in 

 turn is influenced by climate, soil de- 

 velopment, geologic weathering, other 

 biota, and natural disturbances. Ex- 

 amples of some forest influences 

 which directly or indirectly affect 

 water quality include: 



1. An ameliorating influence on 

 local climate leading to lower 



water temperatures and lower 

 evaporation rates and also, usu- 

 ally, to greater transpiration 

 rates and higher production of 

 atmospheric oxygen. 



2. A favorable influence in reduc- 

 ing flooding levels, erosion, 

 and consequent sedimentation 

 production and turbidity in 

 streams. 



3. A favorable influence in the 

 area of nutrient cycling; more 

 nutrients are held in and on 

 forest land. 



4. High production of organic 

 matter may produce short-term 

 discoloration, and sometimes 

 odors, in surface water. At the 

 same time, this organic material 

 has a very favorable influence 

 on biotic activity in and on soil. 



5. Forest vegetation, particularly 

 deep-rooted types, tend to pro- 

 vide optimum natural protec- 

 tion against avalanching and 

 landslides. 



6. Forests generally consume more 

 water than other vegetation; 

 thus, less total water may be 

 available downstream for dilu- 

 tion. 



7. Forests tend to buffer highs and 

 lows of streamflow volume and 

 the quality of this water. 



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