|
<br />15
<br />
<br />N
<br />C')
<br />N
<br />~'1
<br />
<br />original USDA planning documents on Grand valley, Lower Gunnison,
<br />and McElmo Creek units assumed that 95% of the return flow was
<br />surface runoff and 5% was deep percolation. Salinity program
<br />monitoring for irrigation the in Grand Valley on over 166 fields
<br />for the entire irrigation season, on several crops, soils, and
<br />irrigation methods, docments that about 50% of the return flow is
<br />deep percolation and 50% is surface runoff. Over ten feet of
<br />deep percolation for the season has been monitored on two
<br />different fields. One irrigated with a sprinkler system and the
<br />other with a surface system.
<br />
<br />Conservationists had contributed to the problem for over 25 years
<br />by recommending leaching or "blackening across" in the spring to
<br />leach salts. Special leaChing for salinity is not needed as the
<br />quality of the irrigation water is excellent, usually less than
<br />400 mg/L. Since the start of the salinity control program no
<br />specific leaching fraction has been recommended in the spring.
<br />
<br />The water and salt budgets developed for Grand Valley in 1993
<br />based on monitoring and evaluation by USDA, ARS, CSU, USGS and
<br />the Bureau show a change in potential salt load reduction. The
<br />revised salt load reduction from the USDA program is 132,000
<br />tons/year or about 100,000 tons/year less than the anticipated
<br />reduction shown in the 1977 and 1980 USDA reports. The total
<br />salt loading for present conditions from onfarm deep percolation
<br />is significantly greater than the 1977 estimate because of
<br />current information on deep percolation. The expected seepage
<br />and salt load reduction from field ditches and laterals is less
<br />because monitoring showed that water was in farm and field
<br />ditches about one third the time originally assumed. The
<br />assumptions for Grand Valley in the water and salt computations
<br />are similiar to areas in Lower Gunnison and the McElmo salinity
<br />control units. _,..L""/,\":\,t\v.-J \ ,...J
<br />~'v'"".'.." ,,),:\..,.-
<br />0'" ,9/ "f
<br />.)"
<br />
<br />Yz.. -f ~.. \,~:':...;J
<br />.,. I ''''
<br />\...JfI.\~~,:'r...l...h ....
<br />~
<br />
<br />Total
<br />
<br />
<br />~)1.l{'
<br />
<br />.' / \l\~ 12.-
<br />// t->";
<br />tons per year ~
<br />1977/1980 Plan ~\~
<br />Total Reduct
<br />
<br />Salt Budget for Grand Valley:
<br />
<br />
<br />USDA
<br />Treatment
<br />x----.
<br />~~90.~~ 664 mi
<br />
<br />60 000 A 53 000 A
<br />
<br />T
<br />
<br />Onfarm
<br />Ditch Seep.
<br />
<br />Dee
<br />
<br />86,000
<br />I
<br />218 700
<br />
<br />32 000
<br />
<br />158,000
<br />
<br />65,000'
<br />
<br />~
<br />
<br />61 000
<br />
<br />-139 000 /68 000
<br />
<br />",
<br />
<br />Off-farm
<br />Laterals
<br />
<br />490 mi
<br />
<br />..-
<br />304,700 93,000 297,000 133,000
<br />
<br />", 'J.ll ".L, I
<br />'r ,.. ~u....... ~
<br />190 mi 100,600 139,000') 100,000
<br />)303,000
<br />172.000 1
<br />
<br />TOTAL ONPAlUl
<br />
<br />Canals(USBR No.)
<br />
<br />TOTAL OFF-FARM
<br />
<br />272,600 39,000 303,000 100,000
<br />
<br />..>>--..
<br />\-;-z..
<br />
<br />..- ,
<br />577.300 132.000' 600,000 233,000
<br />~~ " .'
<br />~ .'0'---.-), _::--1
<br />~~:~:~ L A
<br />~ ';p' ~ \1 \ '\\J) )"0c
<br />
<br />TOTAL
<br />
|