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L" .-4 N o (l -, , ," CHAP:rER." IV CONSULTATION AND COORDINATION COMMENT LETTERS RONALD JOHNSTON, PROJECTS MANAGER JULY 16. 1990 PAGE 4 The DEA addressed impacts that deletions of detention dams and ditches would cause to wildlife, but not impacts to the canal or the land between the Stubb Ditch and the Government Highline Canal. According to this DEA, the Stubb Ditch will be filled in and the irrigating water carried in a buried pipe line (this is not addressed in the DEA). There will be nothing between the north side of 1-70 and the Government Highline to stop water racing off the BLM lands which are denuded of vegetation for the most part. It is slated it courd -cause the canal to fail." Then what? What is to be done to prevent this from happening? Water in this magnitude of volume carries large quantities of silt that contains salts. It is obvious the situation has not improved since 1977. .Operation of the Government Highline Canal is somewhat complicated by the failure of numerous cross-drainage structures to convey natural flows from the Book Cliffs across the canal to natural drains connected with the Colorado RiVer. The majority of these structures have been rendered inoperable by the accumulation of silt and debris over the 60 years of project operation, and some have been closed for so long that farming operations have eliminated the drainage channels below the culverts. Only the major cross-drainage structures still convey water under the canal, and the flows from the other drains accumulate behind the canal until they overtop the upper bank and either flow down the canal or over the downhill bank, The flows thus introduced into the canal bring with them sediment and debris which have to be cleaned from the canal regularly. In some places, the downhill bank has been lowered to allow flows to wash over it without eroding the bank. A special cross-drainage problem exists along the Stub Ditch and the Government Highline Canal between the Price-Stub Pumping Plant and the terminus of the Stub Ditch. The natural drainage system in this area has been interrupted and altered by the construction of Interstate Highway 70. Most of the hi9h';/ay cross- drainage structures empty into the Stub Ditch, but a small number cross the ditch and empty directly onto cultivated fields. Flows in the $1'-c::J Ditch sometimes exceed its capacity, and they spill onto fields, county rC.:lds, or whatever lies downhill, .Current operation and maintenance practices include monitor';'lg of weather conditions to determine when high natural runoff would ct.:::ur, System employees then open wasteways on the canal to release excess flows down existing drains to prevent overflows and washouts on the lower bank. When sediment and debris accumulate to such an extent as to interfere with proper flows, they are removed by dragline and backhoe. When excess flows overtop the lower bank. crop damage and additional maintenance expense on ditches is incurred by farmers immediately below the canal. Very little maintenance has been conducted to preserve 52