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Arkansas River channel that has restricted and continues to confine the river channel such as that in the La Junta area (Aerial Photograph 1). The diversion of irrigation water and sediment by the Ft. Lyon Canal diversion structures, located between 1 and 2 miles upstream of Channel Problem Area No.1 (Figure 2), and the canal's partial return of sluiced sediments to a dewatered river channel are most likely having some effect on sediment transport in Channel Problem Area No. 1. Human encroachment on the floodplain in theLa Junta area also contributes to the channel problem by restricting the movement of flood flows through the area (Aerial Photograph 1). Encroachment on the floodplain and on the river channel by agricultural lands is continuing to occur throughout the Arkansas River Valley (Aerial Photographs 1 and 2). Between the Ft. Lyon diversion structures and the State Highway 109 bridge downstream, there are three locations where the river's floodplain is constricted by human development; Constricted Floodplain Points A, B, and C as shown on Aerial Photograph 1. In this area, the river channel measures approximately 135 feet in width. At Constricted Floodplain Point A the floodplain measures about 530 feet in width, at Constricted Floodplain Point B near the old railroad roundhouse the floodplain measures about 265 feet in width, and Constricted Floodplain Point C at the State Highway 109 Bridge the floodplain also measures about 265 feet in width. These three constriction points significantly hamper the movement of flood flows through the La Junta area. The Arkansas River is also continuing to experience authorized and unauthorized channel modification at numerous locations. Two examples in the area of Channel Problem Area No.2 are provided (Aerial Photographs 3 and 4; USACE 1994). Channel Problem Area No.2 is located at the upstream end of the Las Animas Levee (Aerial Photograph 3, Figure 2). The Las Animas Levee Project (US ACE 1968), constructed in 1977-1978, includes about 9.3 miles of levee on the south side of the river that protects agricultural lands and the city of Las Animas and a short 1.0-mile levee on the north side of the river immediately north of Las Animas. The channel problem at Channel Problem Area No.2 was not a problem until the levee was constructed and encroached on the river channel. The problem now is that the Arkansas River wants to continue to use a channel meander, thereby threatening the levee during flood flow events, and human activity, subsequent to levee construction, has tried to divert and straighten the river at this location through channelization efforts and the construction of rock groins to divert the river away from the levee. Downstream of Channel Problem Area No.2, sediment from Horse and Adobe Creeks enter the Arkansas River. The channelization at Channel Problem Area No.2 increases the velocity of river flows downstream of the channelization and at the Horse and Adobe Creek confluences the river attempts to transport the increased sediment. Immediately downstream, the river tends to slow again and tries to regain equilibrium as evidenced by the sediment deposition and wide meanders (Aerial Photograph 5). Construction of the Las Animas Levee project not only constricted the floodplain but also channelized a portion of the river downstream of Channel Problem Area No.2 and upstream of Las Animas and Channel Problem Area No.3 (Figure 2). Abandoning the recent historic channel area, the levee project constructed a new straight channel from about 3.5 miles upstream to about 0.75 miles downstream of the U.S. Highway 50 Bridge located north of Las Animas. A portion of the Horse and Adobe Creeks sediment is also transported into the approximately 4- mile straightened channel at Las Animas. Aerial photography provides views of significant 50 I I I I I I I I I I I I I I I I I I I