Natural Resources, Water Rights

Rule R655-11

Requirement for the Design, Construction and Abandonment of Dams

Notice of Proposed Rule

(Amendment)

DAR File No.: 34960
Filed: 06/22/2011 03:11:15 PM

RULE ANALYSIS

Purpose of the rule or reason for the change:

The current rule requires clarification and update to current industry practice.

Summary of the rule or change:

In Subsection R655-11-6A(B), makes a clarification. In Subsection R655-11-6E(G), updates to current industry practice. In Subsection R655-11-6E(I), makes a clarification. In Subsection R655-11-7A(A), updates to current industry practice. In Subsection R655-11-7C(J), makes a clarification and updates to current industry practice. In Section R655-11-10D, makes a clarification and updates to current industry practice. In Section R655-11-12B, makes a clarification. In Subsection R655-11-12E, makes a clarification and updates to current industry practice.

State statutory or constitutional authorization for this rule:

• Title 73, Chapter 5a

Anticipated cost or savings to:

the state budget:

No cost involved, clarification of processing does not require a dollar figure.

local governments:

No cost involved, clarification of processing does not require a dollar figure.

small businesses:

No cost involved, clarification of processing does not require a dollar figure.

persons other than small businesses, businesses, or local governmental entities:

No cost involved, clarification of processing does not require a dollar figure.

Compliance costs for affected persons:

No cost involved, clarification of processing does not require a dollar figure.

Comments by the department head on the fiscal impact the rule may have on businesses:

No physical impact, clarification of process procedures does not require a dollar figure.

Michael Styler, Executive Director

The full text of this rule may be inspected, during regular business hours, at the Division of Administrative Rules, or at:

Natural Resources
Water Rights
1594 W NORTH TEMPLE
SALT LAKE CITY, UT 84116-3154

Direct questions regarding this rule to:

• Marianne Burbidge at the above address, by phone at 801-538-7370, by FAX at 801-538-7467, or by Internet E-mail at marianneburbidge@utah.gov

Interested persons may present their views on this rule by submitting written comments to the address above no later than 5:00 p.m. on:

08/15/2011

This rule may become effective on:

11/12/2011

Authorized by:

Michael Styler, Executive Director

R655. Natural Resources, Water Rights.

R655-11. Requirements for the Design, Construction and Abandonment of Dams.

R655-11-6A. Factors of Safety.

A. All dams should meet the following criteria for factors of safety under normal loading conditions.

 

TABLE

                                                 Minimum Factor

   Condition                                        of Safety



   End of Construction Case--upstream and

     downstream slopes                                 1.3

   Steady State Seepage--upstream and downstream

     slopes (full pool)                                1.5

   Instantaneous Drawdown--upstream slope              1.2

    OR

   Actual Drawdown--upstream slope                     1.5

 

B. All factors of safety should be generated by methodology acceptable to the State Engineer. In undertaking the analysis, the effects of anisotropy should be considered and a ratio of horizontal to vertical permeability of at least nine should be used in the seepage analysis , unless otherwise justified to the satisfaction of the State Engineer. Ratios of up to 100 should be considered if the material types and construction techniques will cause excessive stratification.

C. The strengths used in the stability analysis should be obtained from tests which best model the situation being analyzed.

D. The analysis of the upstream slope stability for actual drawdown should consider drawdown rates which the low level outlets are capable of generating. Actual residual pore pressures should be used.

E. For low hazard dams the State Engineer may waive the requirements of a stability analysis, including a seismic analysis, if it can be demonstrated that conservative slopes and competent materials are used in the dam, and seismic problems (i.e., liquefiable materials, active faults close to the dam) are not present.

F. Stability evaluations where residual strengths are used must have a minimum factor of safety of 1.3.

 

R655-11-6E. Internal Drainage.

A. All underdrains and collection pipes shall be constructed using non-corrodible materials capable of withstanding the anticipated loads.

B. Underdrains and collection pipes should be designed to conduct flows several times larger than anticipated. All pipes within the dam which are not easily accessible shall have a minimum diameter of six inches.

C. All internal drain pipes should be enveloped with free draining material, meeting filter requirements with adjacent zones.

D. Where multiple pipes are used to conduct drainage from internal portions of the dam, they should be carried to the downstream toe or gallery separately without intervening connections or manifold systems. If the drain pipes are connected at their termination points, manholes should be provided to facilitate observation and measurement of the separate drain lines.

E. All underdrains and collection pipes should have provisions for measuring discharges in manholes or at their discharge points. If the anticipated discharge is in excess of 10 gallons per minute (gpm), a weir or other suitable measuring device should be provided. If the anticipated flows are less than 10 gpm, provisions should be made so the water can be discharged freely into a vessel 1.5 feet high and one foot in diameter.

F. All exposed underdrain and collection pipes shall have an appropriate rodent screen attached.

G. All underdrains and collection pipes [should]shall be cleaned out and inspected by camera prior to the first filling of the reservoir.

H. All seepage collection systems must include a collection pipe to discharge flows.

I. All internal drains must have a sufficient[minimum] cover [of 3 feet] of impermeable material to eliminate the collection of surface waters.

 

R655-11-7. Outlet Requirements.

All outlet designs should meet the following criteria.

 

R655-11-7A. Outlet Sizing.

A. All dams shall have a low level outlet capable of draining the reservoir[ to the sediment pool]. Exemptions to this requirement may be granted at the discretion of the State Engineer. Normally, exemptions will only be considered for low head, low hazard dams. Any dead storage must be approved by the State Engineer and must be sufficiently low to eliminate any storage hazard. The outlet should be sized to meet the project demands as well as the following criteria.

1. All outlets shall be 24 inches in diameter or larger unless exempted in writing by the State Engineer. Outlets should have valves or capped flanges which can facilitate entry into the pipe by personnel or video equipment.

2. All outlets shall have the capacity to evacuate 90% of the active storage capacity of the reservoir within 30 days neglecting reservoir inflows. The State Engineer may adjust this requirement on large reservoirs if it can be demonstrated that compliance would result in an unreasonably sized outlet or potential releases would exceed the downstream channel carrying capacity.

3. All outlets shall have the capacity to satisfy prior downstream water rights and the owners' release requirements.

 

R655-11-7C. Outlet Details.

A. All outlets shall have a trash rack to prevent clogging.

B. All outlets connected directly to a downstream pipeline shall have an emergency bypass valve.

C. All outlets shall have a suitable energy dissipator at the discharge end to prevent erosion of the downstream channel.

D. All outlets will be placed on a concrete cradle or encased in concrete unless specifically exempted by the State Engineer in writing.

E. All outlets, with the exception of ungated outlets, shall have an operating gate or a guard gate on the upstream end.

F. All outlets shall have seepage control measures to reduce the potential for piping along the conduit. Common methods may include locating the outlet conduit in bedrock and installing a conduit filter drain to intercept seepage.

G. Outlets encased in concrete should have battered sides to facilitate compaction against the encasement.

H. Every attempt should be made to locate the outlet on bedrock or consolidated materials. In the event this is not possible, consideration should be given to articulating the outlet to allow for settlement.

I. Outlet gates and valves can be either mechanically or hydraulically operated. In either case the hydraulic lines or mechanical stems must be adequately protected from debris, wave action, settlement, and ice damage. Buried stems should be encased in an oil-filled pipe supported on pedestals. No catwalks or similar access structures will be allowed on reservoirs where freezing occurs or significant floating debris is present. All outlets which are operated with electrical equipment must have back-up generating capability or a manual bypass system capable of being operated in a reasonable amount of time.

J. All outlets shall be properly vented .[ to avoid cavitation, surging, and reservoir vortexes. On low head dams adequate ventilation may naturally occur through the conduit if a free water surface is maintained. In most cases a] A vent pipe and air manifold around the perimeter of the conduit immediately downstream of the gate will be required unless waived by the State Engineer. The air supply lines should be conservatively sized for the anticipated flows and protected in the same manner as the outlet control lines or stems.

K. All operators and supporting equipment for outlet controls should be properly protected and secured. Particular attention needs to be given to protection from vandals and unauthorized operation. All outlet controls should be clearly marked as to which way the gates and valves operate so that overloading of a closed gate or valve should not occur.

L. Outlet controls should be accessible when the spillways are in use.

 

R655-11-10D. Seepage Measurements.

Seepage measurements for all drains and collection pipes should be provided, as outlined in R655-11-6E, for all high and moderate hazard dams. Any significant seepage areas which develop [following the initial filling should]must be [also be] provided with measuring devices and at the discretion of the State Engineer, must be collected in a filtered drainage system.

 

R655-11-12B. Formal Construction Inspections.

In approving plans the State Engineer may require his approval of certain construction operations before the next phase of construction can commence. The owner's engineer or inspector must notify the State Engineer and determine a mutually acceptable time to observe and approve the work prior to continuation of the construction.[ Written acceptance of work inspected during formal inspections will be sent to the owner and his engineer.]

 

R655-11-12E. Final Inspection.

Before any dam can be placed in operation a final inspection of the project must be undertaken by the State Engineer and his written acceptance of the project received. The Emergency Action Plan, Standard Operating Plan, and Initial Filling Plan, if required, must be completed and approved before final acceptance and authorization for filling can be given. During rehabilitation of existing dams, at the discretion of the State Engineer, some reservoir storage may be allowed provided sufficient safety criteria are adopted. Record drawings[As-constructed plans] of the project must be submitted within 60 days of the date of the final inspection. All record drawings[ as-constructed plans] submitted must be on a high quality reproducible medium or electronic format acceptable to the State Engineer. Record drawings shall[As-constructed plans should] reflect design changes made during construction, geological logs of the foundation excavation, and piezometer borings.

 

KEY: dams, earthquakes, floods, reservoirs

Date of Enactment or Last Substantive Amendment: [December 10, 2003]2011

Notice of Continuation: April 14, 2011

Authorizing, and Implemented or Interpreted Law: 73-5a