Conn_Dam_-_Technical_and_Budget_Proposal_hydroplus.pdf

CONN DAM

USE OF THE FUSEGATE SYSTEM

TECHNICAL & BUDGET PROPOSAL

2023/MSE/077 Rev0

9.32 ft high Fusegate® at Pikes Creek Dam (Pennsylvania)

HYDROPLUS

2023US001

B

A

0 2023-11-07 MSE CDS HKO First issue

Rev. Date Prepared by Reviewed by Approved by Description

INDEX

I. INTRODUCTION

II. BASIC DATA

1. MAIN FEATURES OF THE DAM

2. HYDROLOGICAL DATA

3. RESERVOIR STORAGE CAPACITY

4. MAIN FEATURES OF THE SPILLWAY

4.1. Existing broad crested weir

5. Existing configuration flood routing

III. DESCRIPTION OF THE SOLUTION

1. BASIC DESIGN REQUIREMENTS

2. FUSEGATE SYSTEM CONFIGURATION

3. WET WELL TOWER

IV. FLOOD ROUTING SIMULATION

1. BASIC DATA

2. HYDRAULIC STUDY RESULTS

V. CONCLUSION

VI. BUDGET PROPOSAL

1. Preamble

2. Scope of Works

2.1. Conceptual design

2.2. Detailed design

2.3. Supply of the Fusegate System

3. Exclusions

4. Commercial Proposal

VII. ANNEXES

1. Fusegate Functioning principle

I. INTRODUCTION

Conn dam is located on the Conn Creek near the city of St. Helena, CA, and serves as a drinking water supply dam for the City of Napa.

City of Napa is currently working on developing alternatives to improve the flood discharge potential of the dam and requested Hydroplus to study the application of the

Fusegate System to increase the spillway capacity.

The Fusegate® System is a patented non-mechanical spillway control system, which has gained an international reputation of reliability and robustness. It consists of independent free-standing blocks made in steel or concrete set on a spillway weir and designed to tip-off during extreme flood events when the reservoir level reaches a predetermined elevation. Compared to the mechanical alternatives, the Fusegate System has design simplicity that minimizes the risk of mechanical failure and maximizes reliability and accuracy in flood management. Also, as the Fusegates are a non-mechanical spillway control system with no moving parts, they do not require operational checks or parts replacement.

This proposal serves as a record of the design parameters of the Fusegates to be used at Conn dam based on the data provided by the City of Napa. Other solutions can also be developed to meet any other requirements or to reduce costs.

Figure 1 - Typical 3D rendering of a labyrinth Fusegate

The present proposal serves as a record of the design parameters of the Fusegates to meet the project requirements.

II. BASIC DATA

The data used to perform the study are extracted from the documents supplied to

Hydroplus and are summarized hereafter for ease of reference.

1. MAIN FEATURES OF THE DAM

o Dam type: Rockfill dam o Full Supply Level (FSL): El 315.00 ft o Maximum Water Level (MWL): El. 320.00 ft o Dam crest level: El. 330.00 ft

2. HYDROLOGICAL DATA

For the Conn Dam spillway study, the only flood event to be considered is the PMP flood.

The inflow data are given in the following table:

Time (hrs) Flow (cfs)

0 0

6 500

12 2 730

18 5 314

24 8 045

30 10 716

36 12 507

42 13 652

48 15 002

54 16 060

60 33 881

64.8 42 719

66 42 278

72 31 650

78 15 972

84 6 547

90 2 642

96 998

102 323

108 0

114 0

120 0

126 0

132 0

138 0

144 0

Table 1 – PMP inflow discharge at Conn Dam

3. RESERVOIR STORAGE CAPACITY

Elevation (ft) Volume (acre-ft)

315.00 29,175

316.00 29,894

317.00 30,623

318.00 31,369

319.00 32,104

320.00 32,841

321.00 33,579

322.00 34,316

323.00 35,054

324.00 35,791

325.00 36,529

Table 2 – Reservoir capacity at Conn Dam

4. MAIN FEATURES OF THE SPILLWAY

4.1. EXISTING BROAD CRESTED WEIR

o Type: Free sill o Width: 135.00 ft o Sill crest level: El. 315.00 ft o Weir discharge coefficient: 3.09

5. EXISTING CONFIGURATION FLOOD ROUTING

The flood routing of the PMP flood for the existing configuration shows the following results:

Figure 2 - Flood routing results for the existing spillway aleblanc Highlight aleblanc Callout Confirms W&C's approximation

III. DESCRIPTION OF THE SOLUTION

1. BASIC DESIGN REQUIREMENTS

The purpose of the study is to extend the existing spillway to 255 ft and construct a concrete broad crested weir set at elevation El. 305.5 ft. Toe abutment blocks will be anchored at the downstream end of spillway to prevent Fusegates from sliding.

Fusegates are then accommodated on the spillway sill.

o Full Supply Level (Fusegates Crest): El. 315.00 ft o Spillway Width: El. 255.00 ft o Maximum Water Level (MWL): El. 320.00 ft

2. FUSEGATE SYSTEM CONFIGURATION

The main features of the proposed Fusegate System are given in the following table:

Fusegate type Labyrinth

Fusegates number 18

Fusegate height 9' - 6''

Fusegate width 14' - 2''

Sill width 255 ft

First tipping level El. 318.58 ft

Last tipping level El. 320.00 ft

Table 3 - Fusegates solution main features

Fusegates will be made in precast reinforced concrete. The precast concrete solution is cost effective in terms of fabrication and allows a better product quality control.

All steel items will be stainless-steel.

Rectangle

The toe abutments

Toe abutment blocks are used to prevent Fusegates from sliding under the upstream hydraulic pressure. They are anchored at the downstream end of the spillway sill and are proposed to be made in stainless steel.

Fusegates rotate around the toe abutment blocks when the water level reaches the tipping elevation.

Figure 3 – Steel Toe Abutment blocks – Nam Mang 3 (Laos)

The deflectors

For each activation sequence, only one Fusegate (called Master) is connected to the related inlet well. The tipping of other Fusegates (called Side) belonging to the same activation sequence will occur by filling of their chamber through a connection pipe (PVC or HDPE) installed inside the spillway sill and includes a steel deflector device.

Figure 4 – WHH Master (with well) and a Fusegate WHH Side

Fusegate

WHH Master

Fusegate WHH

Side

The deflector's purpose is to deflect and concentrate the flow into the pipe connected to the Side Fusegate’ s pressure chamber after the Master Fusegate has tipped.

When the Master Fusegate is still in operation on the spillway sill (no tipping), a cover is placed over the deflector orifice to prevent any premature feeding of the Side Fusegate’s chamber. This cap is attached to the Master Fusegate and, therefore, will tip together with the Master Fusegate during its activation, leaving the deflector orifice free.

Figure 5: Deflector next to a Master Fusegate Figure 6: Deflector with cover attached to the Master Fusegate

3. WET WELL TOWER

The Fusegate solution considers the use of protected wells located in a structure (called

Wet Well Tower or Intake Tower) adjacent to the spillway. This configuration offers the following benefits:

• Improving the discharge capacity of the Fusegates.

• Increasing the tipping accuracy for each Fusegate.

• Preventing any impact and accumulation of floating debris on Fusegates and inlet wells,

• Facilitating the inspection of the inlet wells.

This structure, referred to as a wet well tower, will have an opening (protected by a trash-rack) to the reservoir to allow water reaching the inlet wells under static flow conditions.

Each inlet well is connected to the corresponding Fusegate’s chamber through a pipe

(PVC or HDPE) embedded in the spillway sill.

Figure 7 – Inlet wells inside the wet well tower at Terminus dam - CA

Figure 8 - Inlet wells in the wet well tower at Pont-et-Massène dam - France

Figure 9 - Intake tower view from outside at Nam Leuk Dam (Laos)

Figure 10 - Intake tower at Terminus Dam - CA

INTAKE TOWER

INTAKE TOWER

TRASH RACK

IV. FLOOD ROUTING SIMULATION

1. BASIC DATA

Flood routing simulations were undertaken using our in-house software and are based on the following assumptions:

o The discharge over the spillway sill (with all Fusegate having tipped) per unit length can be calculated by the following formula:

Q (ft3/s/ft) = C x H3/2

With H: upstream head [m], C: discharge coefficient of the spillway sill, considered equal to 3.05 o The discharge per unit of length above the Fusegate is given by:

If H < HC, Q (ft3/s/ft) = μ(H) x H3/2

Then Q (ft3/s/ft) = A x H + B

With HC: Fusegate critical height [ft], μ(H): discharge coefficient varying with the upstream head, A, B: Fusegates’ coefficient depending on its geometry,

2. HYDRAULIC STUDY RESULTS

Inflow and outflow hydrographs for the 1st tipping flood and the PMF for the Fusegates are shown below:

Figure 11 - PMP hydrograph for Conn dam

Figure 12 - Hydrograph for first tipping at Conn dam

It will be noted from the above that:

o A Peak inflow flood of more than 16,000 cfs (equal to 38% of the PMF) is passed without tipping of any Fusegates, o The PMF is passed below the Maximum Water Level at El. 320.00 ft.

Max. Inflow 42,719 cfs

Max. Outflow 42,449 cfs

Max. Reservoir Level El. 320.00 ft

Tipped Fusegates 18/18

Table 4 - Flood routing result table for Conn dam

V. CONCLUSION

The proposed Fusegate alternative meets all the project requirements at Conn dam in order to increase the spillway discharge capacity. In addition, the Fusegate System has valuable safety features inherent to the concept:

o Fusegates overturn automatically, responding to those physical forces acting upon them.

o Fusegates are entirely self-operating and do not require any source of power to operate.

o Only minimal maintenance is required compared to other mechanical gates.

o The environmental impact potential has been minimized.

o It will be reminded that the Fusegates will be engineered so that no malfunctions could lead to a tip-off without any significant flood. Abnormal operating conditions may affect the precision of the System but not the reliability of tipping in the event of major flooding.

VI. BUDGET PROPOSAL

1. PREAMBLE

The scope of work in this proposal covers the design, supply and delivery of the complete

Fusegate System as described hereafter.

2. SCOPE OF WORKS

2.1. CONCEPTUAL DESIGN

It includes:

o Preliminary design report defining the Fusegate System and its performance, o Preliminary drawings and specifications

2.2. DETAILED DESIGN

It includes:

o Final design report:

o Mechanical and geometrical definition of the Fusegate System, hydraulic studies, stability of the Fusegates in all working scenarios, effect on stability of external abnormal load cases such as ice, waves, wind set up, earthquakes, impact loading.

o Project documents: Detail design of the Fusegate System (structural design calculations, specifications, all necessary detail design, and shop drawings for

Fusegates fabrication) including spillway and intake tower layout (structural design of the sill and intake tower by others).

o o Maintenance manual: Procedure of inspections to be carried out on the Fusegate

System (annual inspection, 20-year inspection, inspection after a major flood event) and remedial work to be performed if required.

o Quality control plan o Technical assistance: assistance to the A/E for all aspects related to the Fusegate

System (approval, basic data, review of documents, etc.) and technical assistance on site for up to 3 weeks during installation of Fusegates.

2.3. SUPPLY OF THE FUSEGATE SYSTEM

It includes:

o Fabrication of precast concrete Fusegates, o Fabrication of the Fusegates inlet wells and intake tower trash rack, o Fabrication of the Fusegates components such as embedded steel plates and jacking shoes, o Fabrication of ballast blocks, o Fabrication of the embedded stainless-steel toe abutments and deflectors, o Supply of all items required for the watertightness system (steel flanges, EPDM seals, bolts, nuts, washers, etc.), o Transportation of all the components to the dam site,

3. EXCLUSIONS

The following tasks are excluded from Hydroplus’s scope of work:

o Any civil works at the dam site related but not limited to the spillway sill, o Intake tower works, o Assembly and installation of the Fusegates, ballast blocks and inlet wells, o Installation of the watertightness system, o Any specific insurance beyond standard policies, o General sales tax or any other taxes, bonds, customs, or duties.

4. COMMERCIAL PROPOSAL

Type of Fusegates Labyrinth crested

Height / Width of the Fusegates 9' - 6'' / 14' - 2''

Number of Fusegates 18

TOTAL PRICE (including patent fees) $3,950,000

The price is budgetary and have 10% accuracy.

VII. ANNEXES

1. FUSEGATE FUNCTIONING PRINCIPLE

The Fusegate System is based on the following concept:

- Fusegate are free-standing units installed side-by-side on a spillway sill to form a watertight barrier.

- They bear against small abutment blocks set in the sill to prevent them from sliding before they are required to rotate (under extreme flood conditions).

- There is a chamber in the base of each

Fusegate, with drain holes to discharge incidental inflow (due to leaking seals for example).

- An inlet well on the upstream side of the

Fusegate® crest discharges water into the chamber when the headwater reaches a predetermined level. (Well lips on individual

Fusegate® are actually set at different levels).

During very large floods, water entering the chamber over the inlet well causes an uplift pressure to develop in the chamber.

The uplift pressure combined with the hydrostatic pressure (acting from left to right on the adjacent diagram) is sufficient to overcome the restraining forces and the imbalance causes rotation of the unit off the spillway. The Fusegate is then washed away clear of the spillway by the flood.

If the water level continues to rise after the first breach more Fusegate can rotate, all according to pre-determined upstream water levels until eventually there are no more units remaining and the spillway is free to pass the original maximum design flood. Until rotation of the first Fusegate, (for floods of extremely low risk of occurrence), the user has the benefit of the additional storage.

Each Fusegate has a different overturning level, precisely determined by the height of the water inlet and its own unique stability.

The Fusegate have valuable safety features inherent to the concept and not shared by other spillway control systems:

o they tip-off automatically, responding to those physical forces acting upon them.

o they are entirely self-operating and do not require any source of power to operate.

o only minimal maintenance is required compared to other mechanical gates.

The minimum tipping level (defined earlier) constitutes an engineered safeguard which is of vital importance for the people living and working downstream of the dam since it removes the risk of a sudden downstream artificial flood.

Besides the normal operating condition, Fusegate are engineered in such a way that no malfunction (upstream seal removed or drain holes completely blocked) could lead to a tip-off before water is admitted through the well.

Unlike other spillway control systems, Fusegate® units do not have any moving parts and are therefore less subject to wear and tear and to aging. In addition, their massive structure offers little vulnerability to vandalism and, considering their high stability margin, to terrorist threat.

The Fusegate System does not involve any chemical product, which could later involve a pollution of the river stream (such as oil, paint etc.). In addition, the construction materials are chosen to mitigate the visual impact of the rehabilitation.

The Fusegate will be fabricated in concrete and steel. The maintenance and life expectancy of the System are therefore optimal. Unlike most spillway control systems, the construction of the Fusegate themselves can often be undertaken in the state where the project takes place and will thus benefit the local industry.

As the Fusegate® are non-mechanical without any moving parts, they virtually require no maintenance or operational checks to prove their satisfactory operation. Many working scenarios less than optimum and malfunctioning possibilities have been analyzed through model tests performed at several hydraulic laboratories around the world.

However, it is necessary to follow certain inspection and maintenance procedures to monitor the effect of external conditions. It is the duty of the dam owner to take the appropriate measures to maintain the Fusegate in normal working condition (i.e., the conditions prevailing at the time of contract completion), just as his responsibility for maintenance and inspection of the remainder of the dam, in terms of normally applicable dam safety legislation.

For every project, the Hydroplus design package includes an O&M Manual defining the inspection and maintenance operations to be undertaken on the Fusegate® System. It covers the routine inspections to be performed as well as the guidelines to be followed after any damage. During each of the inspections, the Operator in charge of the inspection should complete the relevant inspection forms provided with the O&M Manual.

Inspections include:

o Routine inspections: are generally performed every six months and also after noteworthy events (such as a major flood or an earthquake, etc.). They can be done at the same time with the routine dam safety inspections. They consist of a visual checking of the control areas for any specific problems:

o Annual inspections: consist of a detailed check of the system and require access to the upstream and downstream of Fusegate. There is no maintenance action to be implemented unless some damage is noticed.

o Twenty-year inspections: are generally performed once every twenty years. At this stage, the reservoir level is required to be below the bottom of the Fusegate®. Several operations are to be carried out, including (i) Removal of accumulated debris, (ii)

Cleaning all parts of the Fusegate, (iii) Replacement of damaged nuts and bolts, (iv)

Repair of any damaged concrete, (v) New corrosion protection (in case of the mild steel option) and (vi) Replacement of rubber seals.

Application of the O&M procedures will ensure optimum performance of the Fusegate

System and prolong its service life.

Highlight Twenty-year inspections: are generally performed once every twenty years. At this stage, the reservoir level is required to be below the bottom of the Fusegate®. Several operations are to be carried out, including (i) Removal of accumulated debris, (ii) Cleaning all parts of the Fusegate, (iii) Replacement of damaged nuts and bolts, (iv) Repair of any damaged concrete, (v) New corrosion protection (in case of the mild steel option) and (vi) Replacement of rubber seals.

Application of the O&M procedures will ensure optimum performance of the Fusegate System and prolong its service life.