FLOOD09463 - Laserfiche WebLink

Home Browse Search

North St. Vrain & 51. Vrain Creeks Floodplain Update Town of Lyons North St. Vrain & St. Vrain Creeks Floodplain Update Town of Lyons TABLE 7 NORTH ST. VRAIN - ST. VRAIN CREEK BENCHMARK INFORMATION Boulder County, Bureau of Reclamation (USBR), US Geological Survey (USGS), US Coast & Geodetic Survey (USC&GS), and National Geodetic Survey (NGS). The six were labeled "SVC 9", "SVC 10", "RM1", "CLIFF", "HEADGATE" and "A329", and are shown on the following Benchmark Location Map. POINT ELEVATION GENERAL LOCATION BM SVC 1 5738.49 Brass Cap Monument (BCM) North Side of Co. Rd. 80, approximately 0.9 mi. West Hwy. 36 and Co. Rd. 80 Intersection BM SVC 2 5847.21 BCM South Side Highway 36 approximately, .45 mi. West of Mile Marker 16 BM SVC 3 5757.38 BCM South Side Highway 36 approximately, 0.1 mi. West of Mile Marker 16 BM SVC 4 5614.61 BCM l' West of Highway Right-of-Way Marker, approximately 0.2 mi. West of Mile Marker 17 BM SVC 5 5544.18 Steel Axle in Boulder, South Side of Hwy. 36. approximately 0.7 mi. West of Mile Marker 18 BM SVC 6 5507.67 BCM NOIth Side Highway 36, West of Co. Rd. 71, West of Box Culvert under Hwy. 36 BM SVC 7 5462.15 BCM West Side Highway 36, approximately 0.36 mi. West of Miles Marker 19 BM SVC 8 5448.45 HeM Southwest Comer Intersection of Applevalley Road and Private Drive, approximately 0.72 rni. West of Hwy. 36 and ApplevalIey Road Intersection BM SVC 11 5313.69 HeM near Southeast Fence corner of Sewage Treatment Plant BM SVC 12 5264.18 HeM Near Fence Comer Southwest of Hwy. 66 and Hwy. 36 Intersection BM SVC 13 5239.83 HeM near Southeast Corner Bridge, Co. Rd. 49, approximately .05 mi. South of Hwy. 66 BM SVC 14 5222.24 BCM NOIth Side Railroad, approximately 0.1 mi. West of Mile Marker 30, Hwy. 66 BM SVC 15 5159.46 HeM Northwest Corner Intersection of Co. Rd. 41 and Burlington Northern Railroad BM SVC 16 5138.29 BCM East Side Co. Rd. 41 approximately 0.2 mi. North of Hygiene Road BM SVC 17 5126.81 BCM l' East of Northwest Corner, Section 35-3N-70W, South of Hygiene Road, approximately 0.5 mi. West of Bridge over St. Vrain Creek BM SVC 18 5094.11 BCM East Side of Co. Rd. 35, approximately 0.4 mi. East of Hygiene Road BM SVC 19 5066.19 BCM South Side Co. Rd. 35, approximately 0.4 mi. East of Hygiene Road BM SVC 20 5035.36 BCM near Irrigation Box, North Side Co. Rd. 35, approximately 0.43 mi. West of Airport Road USC&GS J 320 5025.90 BCM Northeast Leg of Tower BRW searched for the three bendunarks, numbered RM1, RM2, and RM3, as shown on the current Flood Insurance Rate Maps (FIRM) Number 08013C0232 F and 08013C0234 F published by FEMA. Only benchmark RM1 was located and subsequently used in the level loop survey. Benchmarks RM2 and RM3 have either been destroyed or were not properly described, and therefore were not included. BRW also located two of the five Boulder County benchmarks within or near the Town limits. Benchmarks SVC9 and SVClO were located and used in the level loop survey. Benchmarks SVCll, SVC12, and SVC13 were in areas where recent construction has been performed. They could not be located and are believed to have been destroyed. Two other published benchmarks were located and included in the survey. The benchmarks are designated "Cliff" and "A329" and were set by NGS and USC&GS, respectively. Another two benchmarks were included in the level loop survey for reference and are designated "Gauging Station" and "2410". A brass cap benchmark set by the USBR on the wingwall of an irrigation canal headgate was also located and was stamped "Bureau of Reclamation BM 7 5303.3241936". However, NVGD published the elevation for benchmark BM7 as 5305.56, an apparent discrepancy of about 2.2 feet. This benchmark, referred to as "Headgate" by BRW, was included in the level loop survey and was found to be at elevation 5305.56 feet (same elevation as published BM7). The brass cap set by the USBR with the incorrect stamped elevation has been a source of contention and confusion with respect to regulated floodplain elevations. BRW has determined that the elevation stamped on the brass cap is incorrect and should not be used. Since the previous floodplain delineation work by Engineering Professionals, Inc. and Love & Associates, Inc. used the Boulder County benchmarks for the aerial topography, BRW performed the survey using the County benchmarks as the datum. A survey level loop was performed establishing and verifying benchmarks through the Town limits. All of the six published benchmarks located in the BRW survey were within a :to.3-foot tolerance. Four new temporary benchmarks were also set and are listed as BMl through BM4. A list of all the benchmarks (permanent and temporary) that were surveyed and included in the level loop is shown in Table 7 A. A Benchmark Location Map showing their approximate location is included. These benchmarks should be used for all future construction to determine regulated floodplain elevations within the Town limits. Floodplaitllnformatiotl Report 30 K,\35600\OO4\FLOODPLAIN INFORMATION REPORr.doc June 1998 Floodplaitl/tlformatiotl Report 31 K\35600\004\FLOODPLAIN INFORMATION REPORT.doc June 1998