Implementing the DCR Dam Break Inundation Zone Regulations with Local Government

Transcription

1 Implementing the DCR Dam Break Inundation Zone Regulations with Local Government By Zhengang (Michael) Wang, Ph.D., P.E., CFM Regional Dam Safety Engineer (Region 1) 98 Alexandria Pike, Suite 33Warrenton, VA Office Phone: (540) October 16, 2014

2 Disclaimer I use some firms plans and inundation studies. Credits belong to whoever performed the studies.

3 Code of Virginia Requirement for development in dam break inundation zones For any development proposed within the boundaries of a dam break inundation zone that has been mapped, the locality shall, (i) review the dam break inundation zone map on file with the locality for the affected impounding structure, (ii) notify the dam owner, and (iii) within 10 days forward a request to DCR to make a determination of the potential impacts of the proposed development on the SDF standards required of the dam.

4 continued If DCR determines that the plan of development would change the SDF standards of the impounding structure, the locality shall not permit development in the dam break inundation zone unless 1) the developer agrees to alter the plan of development so that it does not alter the SDF standard required of the impounding structure; or 2) the developer contributes payment to the necessary upgrades to the affected impounding structure

5 continued The requirements of this subsection shall not apply to any development proposed downstream of a dam for which a dam break inundation zone map is not on file with the locality as of the time of the official submission of a development plan to the locality.

6 Payment by developer or subdivider A. If DCR determines that a plan of development proposed by a developer or subdivider is wholly or partially within a dam break inundation zone and would change the spillway design flood standards of an impounding structure, a locality shall require, prior to its final approval of a subdivision or development, that a developer or subdivider of land submit an engineering study. The study shall provide a contract-ready cost estimate for conducting the upgrades. DCR shall verify that the study conforms to the Board's standards.

7 Payment by developer or subdivider - continued B. Following the completion of the engineering studies in accordance with subsection A, and prior to any development within the dam break inundation zone, a locality shall require that a developer or subdivider of land pay 50 percent of the contract-ready costs for necessary upgrades to an impounding structure attributable to the development or subdivision, together with administrative fees not to exceed one percent of the total amount of payment required or $1,000, whichever is less. Necessary upgrades shall not include costs associated with routine operation, maintenance, and repair, nor shall necessary upgrades include repairs or upgrades to the impounding structure not made necessary by the proposed development or subdivision.

8 Payment by developer or subdivider - continued C. Where a payment under subsection B is required, such payment shall be made by the developer or subdivider in accordance with the following provisions: 1. A locality may elect to receive such payment. 2. If the locality elects not to receive such payment, any payments shall be made to the Dam Safety, Flood Prevention and Protection Assistance Fund. D. No locality shall be required to assume financial responsibility for upgrades except as an owner of an impounding structure.

9 Example 1 DCR Warrenton Office forwarded inundation maps received from simplified dam break study to localities OEM DCR Warrenton Office forwarded the inundation zone maps received from the simplified dam break inundation study to the Office of Emergency Management (OEM) of localities so that the inundation zone maps can be incorporated into the Emergency Operations Plan (EOP) of localities Diguilian Dam, #06102, Fauquier County Little Lake Arrowhead Dam, #17907 and Lake Arrowhead Dam, #17908, Stafford County Other dams

10 Diguilian Dam, # GIS Shapefile Inundation Areas PMF Failure

11 Diguilian Dam, # GIS Shapefile Inundation Areas - Sunny Day Failure

12 Consequence 1 Overtop Sawyer Dam in both PMF failure and Sunny-day failure, inventory # 06103, that is under Agricultural Exemption. (Sawyer Dam is not modeled, the failure of Sawyer Dam is also not modeled)

13 Sawyer Dam, inventory # Evidences: Sawyer Dam: capacity at normal pool 107 acre-ft; capacity at top of dam 258 acre-ft. The capacity between normal pool and top of dam is: = 151 acre-ft DiGiulian Dam: capacity at normal pool 224 acre-ft, capacity at top of dam 275 acre-ft Conclusion: both the PMF failure flood and sunny-day failure flood will overtop Sawyer Dam and cause overtopping failure of Sawyer Dam

14 PMF Failure of DiGiulian Dam and the induced overtopping failure of Sawyer Dam

15 Consequence 2 inundate public roads Inundate County Road 635, Hume Rd, DOT 2010 road count 380, depth x velocity: 6.1 ft x 10 ft/s (No bridge/culvert is modeled) Inundate County Road 734, Washwright Rd, DOT 2010 road count 180, depth x velocity: 4.5 ft x 15 ft/s (No bridge/culvert is modeled) Total road count = = 560

16 Consequence 2-1 inundate County Road 635, Hume Rd, DOT 2010 road count 380, depth x velocity: 6.1 ft x 10 ft/s (No bridge/culvert is modeled)

17 Consequence 2-2 inundate County Road 734, Washwright Rd, DOT 2010 road count 180, depth x velocity: 4.5 ft x 15 ft/s (No bridge/culvert is modeled)

18 For Dams without dam break inundation maps and EAP with OEM, localities can do something: 1. The locality is authorized to map the dam break inundation zone in accordance with criteria set out in the Virginia Impounding Structure Regulations (4VAC 50-20) and recover the costs of such mapping from the owner of an impounding structure for which a dam break inundation zone map is not on file with the locality and a map has not been prepared by the impounding structure owner - Code of Virginia Requirement for development in dam break inundation zones

19 For Dams with inundation maps and EAP with OEM, localities can do something - continued 2. DHS s DSAT can be used to develop EAP, which will be available in spring 2015 as I was told The Dams Sector Analysis Tool (DSAT) is intended to provide Dams Sector partners with secure access to a series of modules and applications covering a range of analytical capabilities. Created in collaboration with the U.S. Army Corps of Engineers, the DSAT serves as an effective Web-based tool to integrate available information on critical infrastructure facilities across the sector. DSAT provides an integrated platform to consolidate analysis tools and data collection mechanisms supporting the screening, prioritization, characterization, and analysis of critical assets. For more information please contact the Dams Sector-Specific Agency at dams@hq.dhs.gov

20 Example 2 Request from Stafford County In July 2013, Stafford County requested DCR to determine the potential impacts of a proposed development on spillway design flood standards of Lake Curtis Dam and Seven Lakes Dam (Virginia Code ) Some lots of the proposed development appear to be encroaching to the Dam Break Inundation Zone of Lake Curtis Dam and Seven Lakes Dam

21 Vicinity Map

22 Area in Concern

23 Topographic Information and Proposed Development

24 Cross Section Layout in HEC-RAS Model Lake Curtis Dam Seven Lakes Dam

25 TOPO

26 Lot #xxx: Lowest Adjacent Grade (LAG) = ft Lake Curtis Dam WSE in PMF w/ Breach: ft Seven Lakes Dam: WSE in PMF w/ Breach: ft

27 DCR s Determination No Impact WSE, PMF Breach(ft) Proposed LAG (ft) LF (ft) Lake Curtis Seven Lakes House Dam, #17912 Dam, #17922 Lot #xxx Lot #xxx Lot #xxx Lot #xxx Lot #xxx Lot #xxx * LAG - Lowest Adjacent Grade * LF - Lowest Floor * WSE - Water Surface Elevation I conclude that the houses at those Lots will not be impacted by the PMF dam failure flood of either Lake Curtis Dam or Seven Lakes Dam if those houses are built as proposed The submitted development will have no potential impact on the spillway design flood standards required of either Lake Curtis Dam or Seven Lakes Dam if it is built as proposed on the submitted grading plan.

28 Code of Virginia Notice to the public A. When applying to the Department for a permit to construct a new high or significant hazard potential impounding structure, the applicant shall provide localities that lie within the inundation zone with copies of the construction permit request and the dam break inundation zone map. B. When submitting the application to the Department, the permit applicant shall publish a notice in a newspaper of general circulation in the affected localities summarizing the permit request and providing the address of locations where copies of the construction permit request and the dam break inundation zone map may be examined. The applicant shall provide copies of the published notice to the Department and to the local government offices with plat and plan approval authority or zoning responsibilities as designated by the locality.

29 Notice to the public - continued C. The Department may hold a public hearing on safety issues associated with the construction permit application for the impounding structure. D. The Department may require a permit applicant to provide other forms of reasonable notice, such as the placement of a sign on the proposed site, to ensure that affected parties have been informed.

30 Notice to the public - continued E. The permit applicant shall send, by certified mail, to each property owner within the dam break inundation zone, a summary of the permit request and the addresses of locations where the map of the dam break inundation zone may be viewed. In the case of a condominium or cooperative, such information shall be sent to each property owner or the owners' association. The permit applicant may rely upon real estate assessment records to identify property owners. If requested by the Department, the applicant shall provide a list of the persons to whom notice has been sent.

31 Example 3 Lake Ashby and Lake Anne in Fauquier County Studied area Lake Ashby Dam, Inventory #06152 Lake Anne Dam, Inventory #06110 Both dams have the same owner and same engineer

32 Draft Plan of Development near Lake Ashby and Lake Anne

33 Timelines from DCR s viewpoint DCR received construction/alteration permit application for Lake Ashby Dam, including dam break inundation study

34 Timelines from DCR s viewpoint I visited the dam and met with owner s engineer at the dam. After that, my review comments were ed to owner s engineer. Major problems: SDF without a breach is the control event, which gave a wider inundation zone than PMF with a breach Emergency spillway should meet either the stability or integrity standards HEC-RAS steady model was used, which could be accepted if no major concern is raised.

35 Chosen breach location at the existing pipes (close to trees)

36 The existing Lake Ashby Dam

37 Timelines from DCR s viewpoint - continued At the County s request, I met with Fauquier County Dept. of Community Development, Zoning and Permitting to discuss a project and answer some questions regarding mapping of these zones. County officials expressed concern from property owners about proposed inundation zone in Lake Wesley As a result, I also requested owner s engineer to use HEC-RAS unsteady model because impacted property owners have concern.

38 Timelines from DCR s viewpoint - continued One month later, I met with Fauquier County Dept. of Community Development and County attorney again, total 5~6 officials, at the County s request. County officials expressed strong concern about proposed inundation zone in Lake Wesley.

39 Timelines from DCR s viewpoint - continued Then I met with owner s engineers. Engineers wanted to confirm my review comments. Engineers didn t understand why I requested HEC-RAS unsteady model. I told them the concern about proposed inundation zone in Lake Wesley from impacted property owners and Fauquier County. I asked the engineers: The dam is really flat, and the breach location can be here, or can be there. Why did you choose that breach location, not elsewhere? Engineers couldn t give me a defendable reason. At my insist during our meeting, I convinced the engineers and we all agreed that the dam may breach somewhere else other than the chosen location.

40 Topographic Information Breach Location #1 is at the proposed emergency spillway

41 Timelines from DCR s viewpoint - continued After the meeting, I made my determination and ed to the owner, engineers, and Fauquier County: (1) The dam may breach somewhere else other than the chosen location. (2) The Different breach location will result in different dam break inundation zone. The dam breach location is uncertain. (3) The submitted dam break inundation zone map is the engineer s selection, not a fact, because the breach location is the engineer s selection. (4) During my meeting with Fauquier County, I felt the safety concern from the property owners around Lake Wesley. Because of the above reasons, I request Fauquier County s acceptance of the selected dam breach location and the resulted dam break inundation zone on behalf the impacted property owners before I recommend an alteration or construction permit for this dam.

42 Follow-ups The dam is modeled to breach at the main stream, at the Breach Location #2. Two alteration permit applications were submitted to DCR Warrenton Office in 2014, the latest application contains fuse plug. A brand-new design was proposed at each application.

43 Follow-ups continued in 2014 Because of the concerns raised by Fauquier County, I see some possible safety issues AGAIN associated with the alteration permit application including a fuse plug for Lake Ashby Dam. The proposed fuse plug is built above the proposed auxiliary spillway which has a concrete level section. The fuse plug is about 2 feet in height, and is to comply with the CLOMR on file. For the latest application, because the proposed alteration to Lake Ashby Dam will enlarge the capacity of the lake and raise the height of the dam, at my judgment, it is subject to at least part of the requirements of Code of Virginia Notice to the public. DCR will meet with Fauquier County to collect any safety concerns/safety issues associated with the proposed fuse plug.

44 Lake Anne Dam, Inventory #06110

45 Proposed by owner s engineer: separate Lake Anne into two lakes, consider two dams, and make one or two dams size-exempt from Dam Safety Regulations.

46 DCR s response For dam safety purpose, DCR considers Lake Willow and Lake Anne as one lake and one dam. The reason is: if two lakes and two dams were considered, both dams should be L shape dams, and the potion that separates two lakes would be a shared potion of two dams. If the shared potion of two dams failed at the same time when any other potion of any dam failed, Lake Willow and Lake Anne would share water and become one lake.

47 Engineer s decisions, with DCR s permission, during a meeting in September 2013 One dam and one lake will be considered for dam safety purpose This dam will have two possible breach locations: one to Lake Brittle, another to Lake Ashby. 100% lake water (both Lake Anne and Lake Willow) will go through each breach location to map the dam break inundation zone. This is similar to FEMA s floodplain mapping on alluvial fan. Both Lake Ashby Dam and Lake Anne Dam will be high hazard dams. Each will have 90% PMP flood spillway capacity.

48 My recommendation and Fauquier County s Reply Even though not required by Regulations, for the sake of future property owners, I recommend engineers to raise the Lowest Adjacent Grade (LAG) of each new house above the water surface elevation in PMF with a breach. Fauquier County Official: We will strive to see that the LAG is above the water surface elevation as you recommend Lowest Floor (LF) with basement (source: FEMA s Lowest Floor Guide)

49 Lessons learnt Breach location of a long dam can determine the inundation zone. The selection of breach location may be the interest of dam owner, developer, impacted property owners, and localities. If localities have safety concerns about a dam project including the resulted dam break inundation zone, please tell DCR directly so that DCR knows them. Within the gray areas, the better and more communications between DCR and localities, the better service DCR and localities can provide to the public, and the less trouble we would have. DCR may need to hold a public hearing if any safety issue associated with Lake Ashby in this construction/alteration permit application still remains.

50 Example 4 At Loudon County s Request, Developer Brought Quail Ridge Dam into Compliance with State Regulations Quail Ridge Dam, #10720, was a low hazard dam without O&M certificate Loudon County Requested Owner/Developer to Have O&M Certificate in order to get zoning permits As a result, one dam owner (the dam has two owners), who is also the developer, worked very hard with DCR. The other owner, as I was told, did nothing. The dam got a regular O&M certificate in November It is still a low hazard dam.

51 Quail Ridge Dam

52 Loudon County s Conditions for Developer/Subdivider Zoning permits for Lots xx-xx shall not be issued until the developer/subdivider has acquired a Conditional or Regular Operation and Maintenance Certificate for the Quail Ridge Lake dam If it is determined that any portion of a lot is located within the dam break inundation zone, then prior to the sale of that lot the developer/subdivider shall provide disclosure in writing to all prospective purchasers that a portion of the lot is located within the dam break inundation zone, accompanied by a map of the affected area and information pertaining to the Impounding Structure Regulations, including the hazard classification of the dam and associated dam inspection requirements.

53 Proposed Development Proposed Development Aerial Photo

54 Inundation Zone in PMF with Breach

55 Inundation Zone in PMF with Breach

56 Look downstream the development is leveled up (on the left side)

57 Comments or questions? Thank you!