Fishery Foundation of California-Bellota Weir maintenance recommendations. Introduction: The Fishery Foundation of California (FFC) began monitoring Chinook salmon and steelhead passage in the lower Calaveras River below New Hogan Dam in Fall 2003. The objective of the monitoring was to assess the timing and relative abundance of upstream migrating adult salmon and steelhead and juvenile outmigration. The monitoring program is funded in part with a grant from the Anadromous Fish Restoration Program (AFRP) to improve salmon and steelhead passage, escapement to spawning grounds, and overall salmon and steelhead production in the Calaveras River. One aspect of the monitoring program was to document actual passage through the newly placed DeNeil ladder and to assess potential passability at various flows. Although no salmonids were observed using the ladder, the FFC was able to document the frequency with which the ladder was passable. The criteria with which the ladder was evaluated were given by George Heise (DFG passage engineer) and are as follows in order of importance: 10 cfs minimum requirement inside of ladder Proper conditions at ladder outlet (Must be adequately covered by downstream water surface to minimize hydraulic leap. This allows fish to swim into rather than jump into the ladder). Debris in ladders (can seriously degrade hydraulics inside of ladder). False attraction flows Slope of the ladder is an important consideration but was not considered as it does not vary. Assuming 10 cfs minimum ladder requirement the ladder was potentially passable due to natural rain events for 43 days or roughly 38% of the monitoring period (Nov-Mar). Actual passability was reduced by 58% to 18 days or 15% of the monitoring period by improper or untimely maintenance (Figure 1).
Days Passable Assuming 10cfs Minimum Ladder Requirement
Nov # Days Upper flashboards Maintenance problems 0 0 0 Dec 10 0 0 Jan 8 0 0 Feb 17 17 12 Mar 8 8 6 Sum % 43 25 18 38 21 15
Figure 1. Number of days by month the Bellota Weir was potentially passable assuming 10 cfs minimum flow requirement in DeNeil ladders. Lower two rows show actual passability due to failure to remove the flashboards in the upper ladder and improper maintenance of the flashboards on both the upper and lower weir crests.
To maximize the number of days the ladders are passable in a given year, the FFC offers the following recommendations:
1) Problem: Flashboards are installed in the upper ladder inlet to maintain adequate upstream water surface elevation for diversion purposes during low flows (<10cfs)(Figure 2). These were not removed at anytime during the first half of the migration period and the upper ladder was therefore not functional until mid January.
Figure 2. (left)Upstream view of upper ladder with flashboards installed, 15Dec03 (Q=11cfs). (right) Close up of flashboards at inlet of upper ladder 23Feb04 (Q=7cfs)
Recommendation: A system must be developed by which the flashboards can be taken out as soon as flows exceed 10 cfs. We suggest removing the boards at the onset of a flow increase (remotely if safety is an issue) and not replacing them until it is absolutely necessary for SEWD operations. As an alternative, we suggest modifying the current operation of the diversion structure so that the ladder flashboards are no longer needed. The second option, if possible, would eliminate the need for time consuming and often inconsistent maintenance and would ensure that the ladder is functional for the maximum amount of time. 2) Problem: There is often significant leakage in the flashboards surrounding the upper ladder. This creates false attraction flows and fails to utilize all of the available water during low flow periods (<50 cfs). This is especially problematic on the right bank (looking downstream) side of the ladder where sand bags are used in lieu of flashboards. These (sandbags) are often dislodged during moderate flow events and have to be replaced when flows recede to a safe level. In the meantime, there is significant false attraction flow immediately adjacent to the upper ladder outlet and an unacceptable waste of the available water. Likewise, the flashboards on the left bank side of the ladder are not water tight. These do not create a significant attraction flow but water is wasted (Figure 3).
Figure 3. View from right bank of the upper ladder with sandbags installed (right) and with missing sandbags (left). Note the false attraction flow immediately adjacent to ladder and on opposite bank.
Recommendation: The left bank sandbags should be replaced with rigid flashboards so that the need for maintenance is reduced. All flashboards along the weir crest should be made water tight with plastic sheeting during low flows to minimize water waste. This should be closely monitored and maintained when it is safe to do so.
3) Problem: The flashboards in the lower weir control the water surface elevation for both the outlet of the upper ladder and the inlet of the lower ladder. During large flow events, the flashboards in the lower weir are often dislodged. This lowers the water surface elevation in the middle pool and creates a hydraulic leap into the upper ladder (figure 4). This condition is most pronounced at flows below 50 cfs. Failure to replace the boards in a timely manner seriously diminishes both the upper and lower ladders functionality and reduces the amount of time that the ladders are passable.
Figure 4. Downstream view of upper ladder (left) illustrating hydraulic leap at the outlet caused by missing flashboards (right). Picture on right demonstrates proper conditions at outlet of lower ladder and shows missing flashboards on lower weir crest. Both pictures were taken on 20Feb04 (Q=41cfs).
Recommendation: Conditions at the weir should be monitored closely on the descending limb of the hydrograph. As flows receded and when it is safe to do so(<100cfs), all dislodged boards should be replaced to the previous configuration. As an alternative, we suggest constructing an isolated pool between the ladders that would withstand high flows and eliminate the need for the maintenance intensive flashboards. The second option, if possible, would eliminate the need for time consuming and often inconsistent maintenance and would ensure that both ladders are functional for the maximum amount of time. 4) Problem: When the flashboards in the lower weir are installed, there is often significant leakage. At low flows (<50cfs) this creates false attraction flows and wastes water that would otherwise flow through the lower ladder (Figure 5).
Figure 5. (left) Downstream view of both ladders showing leakage through flashboards on 23Feb04 (Q=7 cfs). Note that the upper ladder is completely dry due to flashboards. (right) Side view of lower ladder illustrating significant false attraction flow across lower weir face and gross waste of available water, 6Mar04 (Q=50cfs).
Recommendation: When the flashboards are installed, plastic sheeting should immediately be placed on the upstream side of the boards to eliminate leakage. Sheeting lost to flow events should be replaced as soon as it is safe to do so. As an alternative, we suggest constructing an isolated pool between the ladders that would withstand high flows and eliminate the need for the maintenance intensive flashboards. The second option, if possible, would eliminate the need for time consuming and often inconsistent maintenance and would ensure that both ladders are functional for the maximum amount of time.