STATE OF CALIFORNIA CALIFORNIA NATURAL RESOURCES AGENCY DEPARTMENT OF WATER RESOURCES DIVISION OF SAFETY OF DAMS INSPECTION OF DAM AN D RESERVOI R IN CERTIFIED STATUS Name of Dam San Andreas Dam No. 10-10 County San Mateo Earthfill Type of Spillway Concrete-lined open channel -----------2 feet below spillway crest and 12 feet below dam crest. ---------~ Type of Dam Water is Rain and cold Paul Hu (SFPUC) Reason for Inspection Periodic inspection Weather Conditions ----------------------------------~ Contacts Made Importa nt Observations, Recommendations or Actions Taken The dam has system. According to the owner, the San Andreas Dam Facility Improvement Project is underway. The project team is finalizing a conceptual engineering study which includes for uptake of emergency drawdown. The study was planned to be finalized in Summer 2016. However, DSOD has not received any documents yet. piezometers in the next two years, which is acceptable. The owner plans to Conclusions From the known information and visual inspection, the dam, reservoir, and the appurtenances are judged safe for continued use. Observations and Comments Dam The visible portion of the upstream slope appeared to be satisfactory with no signs of slope instability. The rock rip rap was intact and appeared in good condition (Photo 1). The paved crest was uniform. The downstream slope of the dam also appeared to be satisfactory (Photo 2). Vegetation control on the embankment was good. Seasonal grass on the downstream slope was low enough to allow a thorough visual inspection. I noted no significant rodent activities on the embankment. Spillway The spillway approach , control section and the downstream channel were clear and unobstructed (Photo 3). No apparent concrete or structural deficiencies were noted. The crack sealings on the chute floor remained intact. The stilling basin was not inspected since the old spillway tunnel was passing some flow into the chute. From a distance, a pile of tree debris was observed in the stilling basin, which needs to be removed. Outlet The reservoir has system . The reservoir has operable outlet structures/towers and associated adits: . During the recently completed seismic retrofit project in 2015, the fully exercised with no problems. The log boom was in place and intact. valves were The dam has valve system. Currently, emergency draw down of the reservoir can be done through the which is not acceptable. The owner's conceptual study to use a has not been finalized . DSOD will continue to work with the owner to have valve installed. All gates used for emergency drawdown of the reservoir need to be cycled annually by the owner and in DSOD's presence every three years. Inspected by Photos taken? Yes cc for DWR 1261 (Rev. 10/09) x No Owner/Book Date of Inspection Date of Report Sheet - -1 - of 3 Date of lnspection _ _ _ _ 3/_6_/2_0_1_7_ _ __ Observations and Comments Seepage No signs of seepage were observed either along the downstream toe of the dam or along the groins. The usual seepage through the old tunnel was obscured by water release. Instr. Instrumentation at this dam consists of survey monuments and piezometers. The last instrumentation.data was received on 07/11 /2016 and extends through December 2015. As in the past, most of the piezometer readings were affected by surface water intrusion . The owner plans to retrofit or abandon various piezometers in the next two years, which is acceptable. The phreatic surfaces shown on different cross sections were stable. The maximum settlement from the 1971 baseline continued to be around 0.3-foot at the maximum section (Station 3+00). The annual settlements in the monuments are not significant. Horizontal movements were minimal in the long term and annually. The survey monument readings are acceptable. The existing instrumentation is considered adequate, and no additional instrumentation is judged necessary at this time. Based on the available data and my observation during this inspection, the dam performance is judged satisfactory at this time. Photo 1 - The rock-covered upstream slope of the dam and the paved crest appeared in satisfactory condition. DWR 1261 (rev. 10/09) Sheet 2 of 3 Name of Dam - -San - -Andreas - - - - - - - - - - - - - - - - - - - - - Da. __.fo. - - - - -10-10 ------0 ate of lnspection _ _ _ _3_/_6_/2_0_1_7____ Photo 2 -The downstream slope of the dam appeared to be satisfactory. D --- STATE OF CALIFORNIA CALIFORNIA NATURAL RESOURCES AGENCY DEPARTMENT OF WATER RESOURC ES DIVISION OF SAFETY OF DAMS INSPECTION OF DAM AND RESERVOIR IN CERTIFIED STATU S Name of Dam I Type of Dam Water is San Andreas Dam No. 10.010 - - - - - - - - - County San Mateo _E_a_rt_h_ __ _ __ __ __ Type of Spillway _C_o_n_c_re_t_e_c_h_u_te_ _ _ _ _ __ __ __ _ _ feet below - 10 feet below spillway crest and - 20 dam crest. Mostly sunny and mild Contacts Made Stacy Feng (SFPUC) Reason for Inspection Periodic Maintenance Inspection Weather Conditions Importa nt Observation s, Recommendation s or Action s Ta ken The final inspection for the seismic work on the outlet towers and adits was performed on 5/20/2015. Final close-out paperwork for the alteration application filed on February 11, 2009, and approved on February 16, 2011, was requested from the owner by letter dated 6/15/2015. DSOD is still working with the owner to get a reservoir can be drawn down valve (or valves) installed at this dam so that the Conclusions From the known information and visual inspection, the dam, reservoir, and the appurtenances are judged safe for continued use, pending resolution of the low-level outlet issue. Observations and Comments Dam The downstream face, visible portions of the upstream face, abutment contacts, crest road, and toe area were in satisfactory structural condition with no evidence of instability or distress. Vegetation control was satisfactory. The downstream face was closely mowed, and the trees in the toe area were well-trimmed, allowing for a thfo ugh visual inspection. Rodent activity was still very prevalent. The owner has installed raptor per~es and nesting boxes. As noted previously, the owner is not allowed to use poison bait because of the dam's location in a public park. Spillway The spillway approach , control section , and chute were clear and unobstructed. The concrete was in satisfactory condition . The recent repairs made to the chute wall appeared to be holding up well. Ms. Feng pointed out where the owner will be placing riprap at the end of the energy dissipation structure to reduce potential erosion and undercutting . The owner has also installed a valve through the end wall of the structure to allow the stilling basin to be drained without pumps. The log boom was in place and intact. outlet though the dam . The towers and intake adits were recently retrofitted to mitigate seismic performance issues. The final inspection for this work was performed on 5/20/2015 at which time the outlet gate valves were fully cycled. There is DSOD is still working with the owner to get a (or valves) installed at this dam so that the reservoir can be drawn down without running water through Inspected by Photos taken? Yes cc for DWR 1261 (Rev. 10/09) No Owner/Book x Date of Inspection Date of Report RC .Bowlus 11/5/2015 ~ lZ·kf (,\ ifIF" 12/1712015 ~ INSPECTION OF uAM AND RESERVOIR IN CERTIFli::u STATUS Name of Dam San Andreas Dam No. 10.010 ---------~ Date of lnspection _ _ _ _1_1_/5_/_2_0_15 _ _ __ Observations and Comments Seepage I noted no signs of seepage through the embankment or along the abutment contacts and toe area. There is a minor, longstanding seep through the old spillway tunnel that appeared similar to my previous inspections. Instr. Instrumentation at this dam consists of survey monuments and piezometers. The most recent instrumentation report was received on August 13, 2015, and covers data gathered through December 2014. The embankment has only settled a maximum of 0.3 ft at Station 3+00 (the approximate maximum section) compared to the 1971 baseline. Approximately 0.05 ft of that difference occurred when the monument was reset following repaving of the crest road in 2007. Overall, year-to-year variations are very small, basically within the margin of error of the survey equipment. Horizontal deflection is equally small, with essentially no change from year to year. The piezometer array continues to indicate a relatively low phreatic surface. Many locations have issues with apparent infiltration, and Based on the submitted data, the embankment is performing satisfactorily. Other than the ongoing work on the piezometer array, no additional instrumentation is judged necessary at this time. DWR 1261 (rev. 10/09) Sheet 2 of 2 STATE OF CALIFORNIA NATURAL RESOURCES AGENCY ~ALIFORNIA DEPARTMENT OF WATER RESOURCES DIVISION OF SAFETY OF DAMS INSPECTION OF DAM AND RESERVOI R IN CERTI FIED STATU S Name ofDam San Andreas Dam No. 10-10 Earthfill Type of Spillway 2.5 feet - - below spillway crest and ---- ----------~ Type of Dam Water is County San Mateo Concrete-lined open channel 12.5 feet below dam crest. Weather Conditions Clear and mild Contacts Made Paul Hu during the inspection Reason for Inspection Periodic inspection Important Observations, Recommendations or Action s Taken The application for the seismic retrofit of the outlet towers, tower adits, and outlet tunnels was submitted on January 29, 2009, and was approved on February 16, 2011. The project is completed and DSOD is scheduling the final construction inspection for this work. and the owner is working with URS to I notified Stacy Feng that correct the deficiencies. an alteration application must be filed and approved before the start of construction. As noted in the June 11, 2014 inspection report, the stream channel adjacent to the spillway stilling basin outfall has undergone significant backwash erosion . I reminded Mr. Hu of the need to repair the existing erosion damage with large boulder rip-rap or by other suitable means. Failure to do so may result in under cutting of, and damage to, the stilling basin overflow weir. Conclusions From the known information and visual inspection, the dam, reservoir, and the appurtenances are judged safe for continued use pending the completion of the approved seismic retrofit project. Observations and Comments Dam The visible portions of the upstream and downstream faces, the crest, and the abutment contacts remain in satisfactory condition with no indication of surficial distress or instability. The rock boulder riprap upstream face armor is in good condition, is adequately thick, and provides effective protection for the upstream face and shell. Vegetation control is excellent, and only a few emerging trees and bushes require removal. The embankment is covered in moderately dense ankle to knee tall grass and other moderately tall ground cover that provide protection against erosion without hindering inspection and monitoring for seepage and other defects. Rodent control is also satisfactory and only minor indications of burrowing activity were observed. All large burrows should be collapsed and backfilled with suitable material. Existing owl boxes should be elevated to enhance their attractiveness to potential habitants. Raptor perches should also be considered and are an inexpensive way to increase the effectiveness of local natural predators. Spillway The spillway approach, concrete-lined channel, and stilling basin are open and clear and remain in satisfactory condition. The recent repair of cracks, spalls, and offsets along the spill~ nnel are holding up well. A flow of less than 0.5 gpm was estimated from the at' its confluence with the spillway chute. Inspected by Photos taken? cc for Yes DWR 1261 (Rev. 10/09) x No Owner/Book Date of Inspection Date of Report Sheet -1- Name of Dam San Andreas 10-10 Date of lnspection _ _ _1_4_A~p_r_il_2_0_1_5_ __ Observations and Comments As noted in the June 11, 2014 inspection report, the stream channel adjacent to the spillway stilling basin outfall has undergone significant backwash erosion. I asked Mr. Hu to repair the existing erosion damage with large boulder rip-rap or by other suitable means. Failure to do so may result in under cutting of, and damage to, the stilling basin overflow weir. The current design storm, prepared in August 1983, is for a PMP producing 3, 655 cfs (-831 cfs I sq mi) from the 4.4 square mile drainage area. The spillway capacity is 4,410 cfs which is greater than peak inflow. Total freeboard is 10 feet and the residual freeboard for the design storm is 4. 7 feet. Freeboard is satisfactory. The seismic improvement work related to the outlet towers, adits and piping is complete, and the final construction inspection to verify the adequacy of the work will be scheduled within the next month or two. The retrofitted outlet works consist of two outlet systems designated SAOS2 and SAOS3. from thence into a through the hillside east of the reservoir. The adit runs into the tower, and pipe which conveys reservoir flow The ad its feed into a tower, and from thence into a pipe which also conveys is provided by reservoir flow through hillside east of the reservoir. Downstream control for valves . valve or outfall. The owner is exploring the possibility of There is presently no dedicated installing a suitable valve on the pipe but there are significant challenges to doing so because of , the lack of a suitable natural drainage channel of sufficient capacity, Construction on the outlet systems is complete, but none of the outlet controls were cycled during this inspection. A full demonstration of SAOS2 and SAOS3 outlet control valves, which requires coordination with the Harry Tracy Water Treatment Plant operators, will be made during the upcoming final construction inspection. Seepage The downstream face, groins, and abutments were dry and free of any indication of seepage. Instr. Regularly monitored instrumentation for the dam and reservoir consists of the following: • Nineteen (19) piezometers designated 1 through 15 and 17 through 20. Piezometers 1, 2, 3, 13, and 18 are located through the crest of the dam; piezometers 4 through 10, 14, and 17 are located through the downstream shell; piezometers 11 and 15 are located through the downstream toe, and piezometers 12, 19, and 20 are located through the upstream shell. • Six (6) settlement monuments located on or near the crest and designated -0+65, 0+00, 0+99, 3+00, 4+82, and 6+ 70. DWR 1261 (rev. 10/09) Sheet 2 of 5 Name of Dam San Andreas 10-10 Date of lnspection _ _ _1_4_A_,_p_r_il_2_0_15 _ __ Observations and Comments I reviewed the SFPUC instrumentation report transmitted to DSOD on June 26, 2014; there are no significant changes since the previous instrumentation report submitted June 7, 2013. The 2014 report documents piezometer readings between the data collection period January 2013 through December 2013, and settlement survey data between January 1994 and December 2013. The data, which follows trends reported in the June 11, 2014 inspection report, shows that: • Leaky open well piezometers 1 through 11 have been an ongoing problem at this site. That they track rainfall closely and with large increases in water elevation suggest that their casings and covers are compromised , rendering them unreliable. Open wells No. 1, 2, 3, 4, 6, 7, and 11 will be retrofitted to either open standpipe or vibrating wire piezometers; open wells No. 5 and 8 will be eliminated in favor of redundant wells nearby; and open wells No. 9 and 10 will also be eliminated, but these well locations will be evaluated for possible replacement. • The remaining piezometers continue to track rainfall more closely than reservoir elevation , though less dramatically than piezometers 1 through 11 . • Since the end of 2006, survey monuments show vertical settlement of less than 0.02 feet (0.24 inches), and horizontal movement of less than 0.05 feet (0.6 inches). Neither horizontal nor vertical movements show any indication of accumulation over time, but rather fluctuate around an average value, and are largely within the range of instrumentation error. The SFPUC report concludes that San Andreas dam has performed satisfactorily for the report period. I agree with report's conclusion. The existing instrumentation appears adequate and no additional instrumentation is recommended or required at this time . The upstream face and spillway entrance as seen from the left abutment. DWR 1261 (rev. 10/09) Sheet 3 of 5 Name of Dam San Andreas Date of lnspection _ _ _1_4_A_,p_r_il_2_0_1_5_ __ Vegetation control is excellent, and only a few emerging trees and bushes require removal (circled) . The view above is looking towards the right downstream abutment, the view below is looking towards the left abutment. DWR 1261 (rev. 10/09) Sheet 4 of 5 Name of Dam San Andreas Date of lnspection _ _ _ _ 14_A_,_p_r_il_2_0_1_5_ __ The recent repair of cracks, spalls, and offsets along the spillway channel are holding up well. As noted in the June 11, 2014 inspection report, the stream channel adjacent to the spillway stilling basin outfall has undergone significant backwash erosion. I asked Mr. Hu to repair the existing erosion damage with large boulder rip-rap or by other suitable means. DWR 1261 (rev. 10/09) Sheet - 5 - of 5 STATE OF CALIFORNIA " CALIFORNIA NATURAL RESOURCES AGENCY I 11 DEPARTMENT OF WATER RESOURCES DIVISION OF SAFETY OF DAMS •I FILE COPY INSPECTION OF DAM AND RESERVOIR IN CERTIFIED STATUS San Andreas Dam No. 10-010 County San Mateo ---------Type of Dam Earth Type of Spillway Concrete chute -----------Water is 1.67 feet below spillway crest and - - 11.67 feet below dam crest. -- - Name of Dam WSE448 Weather Conditions Overcast with showers Contacts Made Paul Hu, et al (SFPUC) Reason for Inspection Periodic Maintenance Inspection Important Observations, Recommendations or Actions Taken Work related to the alteration application filed on 1/29/2009 and approved on 2/16/2012 was ongoing. The alteration consists of a seismic retrofit of the outlet towers and adits. The spillway stilling basin was cleared of vegetation and sediment, as requested. I recommended additional clearing of trees/willows in the discharge channel. Rodent activity remains excessive. The owner is actively working to reduce the rodent population, but is not allowed to use poison bait because the dam is located in a park. Conclusions From the known information and visual inspection, the dam, reservoir, and the appurtenances are judged safe for continued use, pending completion of the seismic retrofit of the outlet. Obse rvation s and Comments Dam Spillway The downstream face, visible portion of the upstream face, abutment contacts, crest road, and toe area were in satisfactory structural condition with no evidence of instability or distress. Vegetation control was satisfactory. Rodent activity is still excessive. The owner is actively working to reduce the rodent population, but is not allowed to use poison bait because the dam is located in a park. The watershed supervisor noted that they have spotted a local mountain lion preying on the rodents. The spillway approach, control section, and concrete chute were clear and unobstructed. The stilling basin was cleared of all vegetation and sediment, as requested. Several feet beyond the end of the stilling basin was cleared as well. I recommended clearing more of the willow and tree growth from the downstream channel. The concrete spillway channel was in generally satisfactory condition, with the exception of the popped joint noted previously. Mr. Hu said that the owner is still working on a fix. The problem area is far enough downstream to not be a hazard to the embankment during a spill. Outlet Work related to the alteration application filed on 1/29/2009 and approved on 2/16/2012 was ongoing. The alteration consists of a seismic retrofit of the outlet towers and adits. We did not inspect the outlet towers because of the ongoing construction. Inspected by Photos taken? Yes cc for DWR 1261 (Rev. 10/09) x No Owner/Book Date of Inspection Date of Report RC.Bowlus ~ \t11/8/2012 12131201 2cL{ 1~ Sheet 1 of 4 1 i;/ 1e. l2/rzl ll.-- INSPECTION t,, · DAM AND RESERVOIR IN CERTi. 1ED STATUS Name of Dam San Andreas Date of lnspection _ _ _ _1_1_/_8_/2_0_1_2_ _ __ Photo 4: Upstream face . Vegetation is sprayed periodically. Photo 5: Downstream face. DWR 1261 (rev. 10/09) Sheet 4 - -- of 4