3. Upper Snake Rock Watershed – Idaho
1. 82,000 ha with 70,000 ha cropland (85%).
2. 270 mm annual precipitation, 90 mm May to Sept.
3. Daily rainfall >20 mm only six times during 2005-2008,
five times in 2005.
4. About 40% sprinkler irrigated.
5. Monitoring for the Conservation Effects Assessment
Project (CEAP) began in 2005.
6. • 24 return flow monitoring sites.
• 5 sub-watersheds, 150 to 600 ha, 5 to 50% sprinkler irrigation
7. -1500
-1000
-500
0
500
1000
1971 2005 2006 2007 2008
SuspendedSediment(kg/ha)
Inflow
Outflow
Net
Sediment loss has decreased since 1971 when watershed was 95% furrow irrigated.
USR Watershed
20. Summary
• Sediment loss from the USR has dramatically decreased
since 1970 due to multiple practices.
• No correlation between amount of sprinkler irrigation and
sediment loss among sub-watersheds.
• Sediment and P loss from a farm decreased 90% when
the entire farm was converted to sprinkler irrigation.
• Furrow irrigation management or conversion to sprinkler
irrigation is the key to reducing sediment and
phosphorus losses.