Barr Lake Reservoir Design Modifications for Public Use

In 2019, a change in State Dam Safety regulations allowed the reservoir at Barr Lake to be enlarged.  To protect State Park facilities from the increased water level, ERC undertook a project to identify impacted roads, trails and other infrastructure then design modifications to ensure their continued safe use by the public. Tasks included: developing design drawings and technical specifications to raise 3 gazebo structures, 1 pedestrian bridge, 3,000 linear feet of gravel trail, 800 linear feet of wooden boardwalk on concrete piers, and 3,300 linear feet of gravel road.  The facilities were designed to meet Colorado Parks & Wildlife (CPW) standards and current building codes.  Construction was completed in 2022.

Barr Lake Spillway

The State of Colorado determined that the spillway at Barr Lake was inadequate to safely pass the inflow design storm. ERC was retained to evaluate existing and future conditions and design a spillway upgrade. ERC evaluated extreme precipitation conditions and defined the Probable Maximum Precipitation of 30 inches in a 48-hour period. When routed the storm produced a peak inflow rate of approximately 40,000 cfs with a total runoff volume of 13,000 acre-feet. Hydraulic modeling showed that a 185 spillway was required to safely pass the inflows while maintaining the required freeboard without raising the dam. The design included replacing the existing earthen spillway with a composite concrete, riprap and soil cement spillway. Additionally, over three miles of perimeter dikes were designed and constructed to control water levels during the design event. ERC completed design, permitting and construction management for the project.

Burlington Canal Headworks

ERC designed and oversaw construction to modernize the main Burlington Canal headworks off of the South Platte River. The diversion structure included four main crest gates (two 6 foot gates and two 12 foot gates) a 4’ x 13’ crest gate for bypass flow operations and a 4’x4’ sandout gate all with flow measuring capabilities. ERC’s work included hydraulic modeling, gate design, 404 and floodplain permitting and construction observation. The completed facility has the ability to pass and measure flows up to approximately 1,000 cfs. Gates were designed to fit within the original Burlington diversion structure while improving operational flexibility and safety.

CDWA Culvert Improvement

In 2019, The Church Ditch Water Authority decided to improve a deteriorating culvert crossing under Arapahoe Street in Golden, CO.  ERC was tasked with designing a new culvert and overseeing the construction process.  Tasks included: initial site survey and hydraulic design, structural design, preparation of bid documents, helping select a construction contractor, and managing construction.  The final design piped the ditch under the road and across adjacent property that was difficult to access and maintain.  ERC obtained permits from the City of Golden and the Colorado Department of Transportation (CDOT), and worked closely with adjacent property owners.  Construction was completed before the 2022 water-delivery season.  The final product eliminated stormwater runoff into the ditch, improved hydraulic efficiency and reduced maintenance headaches.

Church Ditch Headgate 53 Retaining Wall

The Church Ditch hired ERC to repair a concrete-block retaining wall holding back high banks along the ditch in Arvada. The wall showed signs of heaving and overturning in several spots due to a poor design and the expansive soils in the area. ERC designed a concrete footer for the existing blocks and a system of steel angles to tie the blocks together. Approximately 800 linear feet of wall was repaired. The sections were between 6 and 10 feet tall. Design work included hydraulics, stability analysis, and permitting. ERC also managed the project by providing construction oversight.

Church Ditch Headworks

In 2016-2017, ERC managed the project to modernize the headworks structure of the Church Ditch on Clear Creek in Golden, Colorado. During the design phase, ERC conducted hydraulic modeling to size new gates. These included two 4-ft by 4-ft Fresno slide gates, a 4-ft Rubicon overshot gate for controlling upstream head, and a 4-ft slide gate for flushing debris. We also worked with the City of Golden and Jefferson County Open Space to permit the project. In the construction phase, ERC provided bid support to select a contractor then provided oversight and observation to ensure a smooth process. The structure includes security fencing, solar power and the ability to operate the gate and measure flows remotely.

Church Ditch Leyden Flush Structure

The Leyden Flush Structure is a turn-out point for Church Ditch to bypass excess flows and flush sediment and other debris from the upper system. In 2017, the Church Ditch hired ERC to design a new structure to replace the leaky gates, old concrete rickety bridges and a manual stop-log system. ERC designed a new structure to include two concrete headwalls, a 12-ft by 4-ft canal slide gate, a 4-ft by 4-ft Rubicon SlipGate for flushing, two steel access bridges, and security fencing. The gates are solar powered and remotely operable. Design work included hydraulic modeling and gate sizing. ERC also managed the project by providing construction oversight.

Community Ditch Improvements

The Community Ditch through Eldorado Canyon was historically one of FRICO’s most difficult sections to maintain of its 400 mile canal system. Bank sloughing, icing, seepage, liner damage and limited access all contributed to operational challenges in this section. FRICO hired ERC to develop a solution that would allow water to be conveyed through this ½ mile section in a more efficient manner. ERC’s solution replaced the open trapezoidal channel with a box culvert. The culvert was designed to fit within the narrow, meandering confines of the old ditch alignment, which allowed for only inches of tolerance in the box design. Maintenance access, which had not existed through this section, was provided on the top of the culvert. Design work included hydraulic modeling, modifications to intake gates and measuring devices, evaluation of rockfall hazards and Boulder County permitting.

Dam Breach Modeling

ERC has completed several dam breach analyses for municipal reservoirs and mining facilities in states such as Colorado, Arizona, Montana, and South Carolina, among others. The analyses have included sizing flow hydrographs resulting from a dam breach, mapping flood inundation extents (using both one-dimensional and two-dimensional modeling methodology), and determining the downstream hazard classification of each dam in respect to local regulations. ERC has also aided in the creation of Emergency Action Plans (EAPs) for the dams where the downstream hazard potential of the dam is found to be great enough to require one.

DDCVDC Design Criteria

In 2021, ERC worked with the Dry Creek Valley Ditch Company (DCVDC) to revise their Design Criteria Manual.  The manual provides guidance for shareholders, developers, and other applicants interested in constructing projects in and around DCVDC facilities.  The criteria describe the design review process, fees, and the technical and administrative requirements for obtaining the necessary permits and agreements to complete a project.  The manual serves as a how-to guide for those interested in developing adjacent to DCVDC facilities and ensures a high standard of technical design and construction to protect the ditch company and its shareholder.  Under the new criteria manual, DCVDC has permitted culvert crossings, ditch relocations/piping, adjacent stormwater detention facilities and other development without impacting ditch operations or maintenance.

Metro 2nd Creek Interceptor

ERC represented FRICO through the design approval process and construction of a major pipeline crossing of the Burlington/O’Brian Canal. To minimize canal shutdown time, a temporary bypass canal sized to convey 150-cfs was constructed. The project was allowed a 48-hour canal shut down window to connect and disconnect the temporary bypass. A 66-inch steel casing pipe containing a 48-inch sewer pipe was constructed across the Burlington/O’Brian Canal while the canal continued to operate through the temporary bypass. The project site is located near a major creek and significant dewatering was required during the project. The project was completed successfully and on-time within the agreed upon schedule and minimized impact to FRICO ‘s water conveyance.

Temporary Bypass

Pipeline Crossing

Temporary Bypass Confluence

Temporary Bypass Removal and Canal Restoration

Standley Lake Monitoring and Dam Break

ERC is responsible for the on-going monitoring and reporting of Standley Lake Dam in Westminster, CO. This large, high-hazard dam provides water to nearly 300,000 residential and is located in a highly urbanized area. ERC completes monthly inspections, monitors reservoir and phreatic levels, evaluates crack gages and inclinometers and provides reports to dam owners and the State Engineers Office. For emergency planning purposes ERC has modeled dam breach scenarios and prepared inundation mapping for use by local emergency managers. We have designed repairs to ancillary facilities including outlet works, the dam’s spillway and the headgate structure that diverts up to approximately 1,000 cfs into the Lake.

United Reservoir North Cell Pump Station

The United Reservoir North Cell Pump Station project consisted of replacing the existing system to accommodate the adjacent enlarged storage reservoir, to improve the functionality of the system, and to better manage excess sediments inherent to the river intake water.  The pump station is used to divert flows from the South Platte River to Barr Lake and United’s North & South cells.  The pump station is fed by or can return flow to the river via three large diameter pipes.  The pump station consists of a connected two-celled wet well structure with a deep (64’) and a shallow (38’) rectangular (25’ x 11”) compartment.  Both high and low head submersible pumps were installed in the wet wells along with discharge piping that allows for a variety of pumping scenarios up to a maximum rate of 50 cfs to Barr Lake.  A gate is located between the two compartments to control hydraulic connectivity between the two wetwells depending on the specific pumping operation in use.   Water is pumped to Barr Lake through a 36” ductile iron pipe.  The system is automated and can be controlled remotely.

A schematic of the system is shown below along followed by a summary of the design components.

To help mitigate problems caused by disruption to the pumping operations and minimize downtime due to maintenance and cleaning of sediments and debris the following controls were included:

• Sediment/Debris basin positioned between the river intake pipes discharge and the shallow wet well. This basin can be accessed via a vac truck hose for solids removal.
• Removeable screens between the river intake pipes discharge and the pumps.
• Low head submersible pumps with a higher solids content threshold.
• Added redundancy with multiple pumps (four 12.5 cfs high head).
• Capability to pump to Barr Lake from either the shallow or deep wet well.
• Built in sprays used to keep silts suspended and prevent a buildup of solids in the shallow wet well.
• Flexibility to close river feed and pump directly from the North Cell if the sediment load from the river is high and there is enough water in the North Cell.

Concrete Wet wells under construction. Deep well~65′ deep; Shallow well ~35′ deep

South River Intake Pipe Connection to Wet Well (Sediment Collection Bay)

Existing Ultraflow Pipe from River with Sliplined Hobas Pipe

Deteriorated Existing Ultraflow Pipe condition

Pump Discharge Header Shallow Well