Blue Diamond

 

You may not notice from inside the casinos that the Las Vegas Strip is at the heart of one of the most difficult-to-manage storm water basins in the world. Recent urban sprawl has created a population of approximately 2 million. This development has significantly increased the hard surface areas associated with rapid runoff. These surfaces, along with steep mountain slopes and the armored desert floor are flooding surface water into the dry desert washes more frequently than any time in recorded history. While the average rainfall in the las Vegas Valley is 4.49 inches, a half inch of rain falling over the entire valley can bring major roads to a standstill. Summer thunderstorms can drop half of the annual rainfall, leading to deaths and major property damage. Water flowing through Las Vegas Valley channels and detention basins can rise as fast as one foot per minute and move as quickly as 30 miles per hour. National statistics show that more deaths occur in floods each year than any other natural disaster. The Clark County Regional Flood Control District was created in early 1985 by a Clark County ordinance to fund and coordinate the construction of flood control facilities. The District was charged with developing and overseeing a coordinated and comprehensive flood control master plan to alleviate flooding in Clark County, and to regulate land use in flood hazard areas. On September 2, 1986, voters approved a quarter cent sales tax to fund construction of regional flood control facilities. In 1987, the regional Flood Control District began receiving sales tax revenues and started constructing flood control projects. It is anticipated that it will take another 25-30 years of construction before the entire Master Plan is completed. The Blue Diamond Watershed, located in the southwest portion of the Las Vegas Valley, totals approximately 131 square miles. While it is comprised mainly of detention basins connected by conveyance facilities, construction has become more difficult as the facilities approach previously developed sections of the city. The Blue Diamond Flood Control Project from Valley View Boulevard to Decatur Boulevard parallels the busy Blue Diamond Road for nearly two miles. With the rapid growth on the southwest side of theValley, Blue Diamond Road has become the major traffic corridor. Precast concrete pipe with a 100-year maintenance-free design life was therefore a natural design choice for any works associated with the roadway. Nearly 10,000 feet of storm sewers were installed in this corridor, including 60-inch diameter reinforced concrete pipes and various sized precast reinforced boxes including 4-foot x 4-foot, 6-foot x 4-foot, 8-foot x 4-foot and 10-foot x 4-foot sections. Concrete pipe comprises the major trunk line along Blue Diamond Road. In addition to traditional concrete pipe installation, a large concrete box culvert was installed at a railroad crossing. The Nevada Department of Transportation and Clark County Flood Control District oversaw this portion of the project. Construction of the dual width 12-foot x 10-foot precast reinforced concrete box culvert required significant coordination of all parties. Hydraulic modeling showed that the existing railroad structure could be damaged from a flash flood with over 4,000cfs of storm water. While it wouuld have been ideal to replace the existing railroad structure, the railroad reuired a construction window of 12 hours of downtime to the existing tracks. Construction of the new embankment over the box culvert and reconstruction of the railroad tracks could not be completed during the available timeframe, although the precast box culvert could be placed quickly and backfilled immediately. It was determined that the dual box culvert could be completed underneath the existing railroad tracks without disturbing the tracks or structure. The initial precast box sections, supplied by Geneva Pipe Company, were set on the upstream side of the tracks as close to the existing structure as possible. Additional sections were placed on the downstream side of the tracks, and then slid underneath the track bed until they were homed with the precast sections on the other side. The construction procedures were simplified by installing concrete footings to grade under the existing structure. The footings were then used to slide the box sections into position. Very fine graphite pellets were placed on the footings, so that a D-6 bulldozer could push the 25-ton sections into place easily. There was no difficulty in maintaining grade, due to the concrete footing. The most challenging part of the procedure was properly aligning the initial sections of the box culvert. Work proceeded uninterrupted, except for the passage of an occasional train. The 140-foot section of precast dual boxes was completed in nearly three days with both ends of the precast culvert being tied into a cast-in-place open channel waterway. Clark County continues to grow at a rapid pace of almost 6,000 residents each month with a current population of 1.9 million people. Although residential development slowed in 2007, public works projects continued to ensure the safety of the many new residents and the 40 million tourists that visit Las Vegas Valley annually.