Concrete placement on April 8, 2005, for the largest of the sculpted concrete drops started at 7:00 am and was completed in the late afternoon. The entire workforce of Naranjo Civil Constructors was involved. This brings new meaning to the term, teamwork.
The District and Army Corps of Engineers (ACOE) have made a concerted effort to coordinate our maintenance eligibility and the ACOE's Section 404 permit programs. To that end we are encouraging joint meetings and site visits. While these programs have different goals and purposes; there are definitely shared objectives. The District has long promoted preservation of floodplains, which also avoids impacts to waters of the United States and associated wetlands. However, not all projects follow the preservation model. The District/ACOE coordination helps to facilitate and streamline the approval process. The other essential partner is of course local government. Throughout the year we have moved towards larger representation at project meetings with positive results.
Private land development projects are responsible for constructing perhaps one-half to two-thirds of the Denver metropolitan area's major drainageway infrastructure. In working with local governments, developers and their consultants, we have also been mindful that major drainageways must be attractive, provide a community asset and represent a "sense of place" in addition to functioning hydraulically. Michelle Leach and I presented papers on this subject at the District’s April workshop and CASFM’s annual conference in September. Many projects require floodplain revisions through the Federal Emergency Management Agency's letter of map revision (LOMR) process. We spend a lot of time mentoring development applicants and their consultants in preparation of LOMRs for development projects.
Matt Erichsen with Kiowa Engineering Corporation and Chris Castelli with Farnsworth Group (center foreground) provided interactive construction observation. The final surface treatment cannot be completely conveyed through design drawings, rather through skilled field control and a willing contractor.
In the field
One of the truly rewarding and enlightening aspects of my position is field operations. I see a lot of projects over the course of a year and some stand out in terms of design and construction execution. One project I’d like to share is the Parker Auto Plaza. As the name implies, the project is located in the Town of Parker, along Baldwin Gulch, approximately 2,000 feet from South Parker Road to Twenty Mile Road. The Town of Parker has committed to using sculptured concrete drop structures after very successful public projects along Sulphur and Tallman Gulches (in cooperation with the District’s Design and Construction, and Maintenance Programs). Baldwin Gulch was realigned and stabilized with four, five-foot, 100-year capacity sculpted concrete drop structures. Kiowa Engineering Corporation was retained to produce the construction plans. This was the first sculpted concrete drop project approved through the District’s Maintenance Eligibility Program. I took a lot of pot shoots at the "natural" drop structures in the "natural" engineered channel, next to the "natural" auto dealership as opposed to our previously stated preservation preference. However, the design included several effective components, which made all the difference as I’ll discuss below.
The Town of Parker and the District agreed to involve the Farnsworth Group in the construction observation of the sculpted drops, based on their previous performance with the Sulphur Gulch project. Another veteran of the Sulphur Gulch Project was Naranjo Civil Constructors. They were again contracted (through a subcontractor arrangement with the site general contractor) to build the channel improvements. Kiowa Engineering Corporation was retained to provide construction observation for the remaining channel improvements. All consultant and construction costs were born by the developer, as is customary in Parker. Several other subcontractors were hired for the Twenty Mile Road crossing.
View from the top of the completed drop towards the Twenty Mile Road culvert crossing. Note the grouted boulder transition and open three-sided concrete box culvert section.
View of the completed project looking upstream from Twenty Mile Road. The large drop structure is in the immediate foreground. The extended approach section is for underground utility protection. The mature cottonwood trees identify the preserved oxbow location.
Concrete placement for sculpted drops is unique. The drop structure featured in the accompanying pictures required 230 cubic yards of concrete. The Naranjo placement team numbered 25 and required a lot of teamwork. Field engineers from both Farnsworth and Kiowa were present for the entire pour. Concrete delivery proved to be the critical path and stretched the placement time for this largest and final drop to 8 hours. A similar grouted sloping boulder drop would have resulted in half the quantity of grout and placement time. Therefore, cold or hot weather placement could become a significant factor with sculpted drops. An overhead power line through the middle of this site necessitated the use of two concrete pumper trucks, and each pumper crew included the operator, a power line spotter and supervisor. Concrete delivery was staged at two locations and included supervisors and quality control personnel in addition to truck drivers. The general contractor sent a delegation to observe the concrete placement, as did the Town of Parker. Altogether I counted 50 people on site. Obviously, a lot of expertise, coordination and teamwork are required to successfully execute a sculpted drop design. We are told the sculpted concrete drops are similar in cost to comparable grouted sloping boulder drops.
Several other features of this project are worth noting. First, the Twenty Mile Road crossing was designed as a single-span, three-sided concrete box culvert with a pedestrian trail and grouted boulder low flow channel. Notice in the included picture how open the section is, allowing continuous sheet flow from the trail to the low flow channel. The benefits in terms of increased light, safety and appearance, and reduced maintenance are obvious. Another important feature in overall corridor experience is landscape design. I think thoughtful and skilled surface restoration is essential to the overall project success. And finally, the design consultant team was able to preserve one of the pre-project stream oxbows. It is outside of the realigned low flow channel, but within the 100-year floodplain and receives sustaining water from storm sewer outlets.
My compliments to everyone involved in the Parker Auto Plaza for creating a channelization project that sets the bar for excellence in future major drainageway projects.