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<br />G, Step 4. Evaluate latE!ral stability. <br /> <br />1, Los Gatos Creek has widened its channel since construction of the <br />1-5 bridges, possibly because of the additional discharge from the <br />channelization of Chino Creek and confluence effects, <br /> <br />2, Upstream of the bridge, the channel is 91 - 122 m (300- 400 feet) <br />wide, Just upstream of the bridge, the channel is 98.15 m (322 feet) <br />wide. <br /> <br />3, Downstream the channel narrows to 46-76 m (150 to 250 feet) wide, <br />probably as a result of the brid!Je. <br /> <br />4. Lateral instability resulted in poor alignment and a high angle of <br />attack at the bridge, <br /> <br />H, Step 5. Evaluate vertical stability, <br /> <br />1. The stream has had a significant increase in slope after the bridge <br />was built because of the subsidence. <br /> <br />2, The stream degraded 6 feet within 2 years after the bridge was built. <br /> <br />3, A 1980 inspection showed the stream bed generally 1.5 - 24 m (5-8 <br />feet) below original ground elevation. <br /> <br />4. By March 1995, the stream bed had degraded 2.4 - 3 m (8-10 feet) <br />since the bridge was built. <br /> <br />I. Step 6. Evaluate channel respons1e' to change, <br /> <br />1, The knowledge and insight developed from evaluation of present and <br />historical channel and waterslled conditions, as developed from <br />Steps 1 through 5, provide an understanding of potential channel <br />response to previous impacts and/or proposed changes. <br /> <br />2, For Los Gatos Creek: <br /> <br />. <br /> <br />Significant changes occurred due to subsidence (increase in <br />slope), long-term degradation (loss of column embedment), <br />and increase in width upstream (poor alignment and high <br />angle of attack). <br /> <br />. <br /> <br />The stream will continue to degrade but slowly. <br /> <br />4.13 <br />