One of South Weber's many beautiful qualities is the slopes on the south side of the city. According to our general plan, these slopes are considered sensitive lands.
2019 Sensitive Lands Map #5
Our projected general plan has an entire section dedicated to our slopes. In lines 318-336 it states:
- STEEP SLOPES: Steep slopes are found along the south bench area of the City, along the foothill area of the Wasatch Mountains on the east side of the city, and at spot locations throughout the City. These slopes should be considered fragile from a development standpoint and will be required to comply with the Sensitive Lands Ordinance (Ord 10-14). Building roads and subdivisions within them could cause environmental damage, destabilize hillsides and create a hillside scar/eyesore, due to the necessity of cuts and fills to do so. There could be a great hazard of erosion and flooding should denuding result from development efforts without any mitigation efforts applied. These steep slope areas generally coincide with the location of the known faults. These areas are also important to wildlife habitat areas including high value deer winter range. They represent a significant fire hazard to structures which might be tucked within the heavy vegetation located there. In addition, these steep foothills are very important view shed areas for residents as well as passers-by. The mountains are such a prominent feature of the landscape that the eye is constantly drawn to them and their foothills. Should this landscape become scarred up due to development, or for any other reason, would be a significant reduction in the community's overall quality of life. These steep slopes are hazardous areas for development and are important community assets. They are ecologically fragile and should be protected as much as possible.
The general plan summary also goes over landslides on our slopes. Lines 281-290 states
- LAND SLIDES: South Weber sits in a river valley formed in ancient times as the Weber River cut through an alluvial fan deposited there in even more ancient times when Lake Bonneville covered the entire region. As the river cut down through this alluvial fan, it left steep bluffs on the sides. One of these bluffs is on the south side of town running its length. This bluff has been identified in at least two geologic studies1 as having very high potential for landslides. In fact, there is ample evidence of both ancient and more recent slope failure activity along this bluff. When development of any nature is proposed on or near this bluff, it will be important to determine the safety of such development as far as possible. It may be necessary to require mitigation of the hazard or even to prevent the development from occurring. (See Sensitive Lands Map #5)
Course of South Bench Drive is highlighted above, South Weber Projected 2019 Land Use Map
So it may be confusing to many why the trajectory of South Bench Drive, a proposed main thorough-fare through South Weber goes right on those sensitive lands. The city has assured us this road will be built safely and that many studies will be done. Thankfully, many studies have already been done.
Jacqui Layton is a resident of South Weber. When she learned of the proposed road, specifically 1900 E coming in, she had concerns of the safety of this road. She did some research and found so many studies that have already been done. I will link all her sources below, but today I would like to focus on a very thorough and interesting one.
This report is a Utah Geological Study, a division of the Utah Department of Natural Resources.
This study reviews every single landslide or unstable recording of land in Utah. South Weber City comes in second place on studies, with Layton being number 1.
Three areas are focused on in this study. Two landslides, one on 425 East that happened on February 21, 2005 (page 25) and another on 1650 E that happened on April 9, 2006 (page 164) are documented as well as a geotechnical study done near Silverleaf that yielded some concerns (page 349).
425 East Landslide
On page 28, the study states:
"The landslide occurred shortly after 6 p.m., and demolished a barn, took out telephone poles, and blocked State Route 60 (South Weber Drive) (figures 2, 3, 4). The landslide is approximately 480 feet long and 80 feet wide at its widest point (figure 3) and between stations 305 and 310 on the Davis-Weber Canal. According to Nolan Birt (verbal communication, March 4, 2005), the barn owner who witnessed the event, the total landslide travel time was about a minute and the barn provided no resistance to landslide movement. Based on this approximate travel time, the estimated landslide velocity is about 8 feet per second, which classifies as very rapid landslide movement (Cruden and Varnes, 1996). The landslide is just below the Davis- Weber Canal and likely started moving as a rotational slide, but likely transformed into a rapid earth flow about midway downslope and ran out 150 feet beyond the toe of the slope across State Route 60 and onto a flat field. Grass, shrubs, and trees cover this northeast-facing slope. Some trees were rafted on top of the landslide debris (figure 4)"
This study goes on to say that that Terracon completed a slope-stability investigation in January of 2005. This investigation estimated a static factor fo safety to a 1.0 for the slope below the canal (typical safety standard is 1.5 or higher). For earthquake ground shaking conditions, Terracon estimated the factor of safety to be well below 1.0, meaning the slope would fail during an earthquake.
1650 E Landslide
On page 171 the study states:
"The 1650 East landslide was a rapid earth flow that started as a slide at the slope crest adjacent to a pond in a gravel pit (figures 2 and 5). The landslide main scarp extends a short distance back from the slope crest onto flat ground toward the pond in the gravel pit. The landslide is mostly a failure of fill pushed out of the gravel pit onto the upper slope to form a berm along the slope crest (figure 6). The landslide also involved native materials underlying and downslope of the fill. The slide at the crest mobilized into a flow that accelerated rapidly downslope, removing trees and crossing dirt roads, the canal, and a rock wall at the back of the lot before impacting the house at 7687 South 1650 East (figures 2 and 7). The landslide impact broke through the house and garage walls and a small volume of sediment and tree debris was deposited in the house. A child inside the house was injured and the landslide impacted with sufficient force to break part of the house foundation wall (figure 8). The impact to the back of the garage pushed a car and pickup out through the garage doors. The landslide broke windows at the adjacent house to the southwest at 1650 East 7701 South. The landslide also damaged the Davis-Weber Canal which had recently been enclosed in a concrete box culvert but was not yet covered with backfill (Ray, 2006) (figure 9). Water had not yet been turned into the canal for the irrigation season so obstruction to flow in the canal by the landslide was not an issue."
This report is especially concerning because the static factor is at 1.2, well below the normally accepted 1.5 factor of safety. But what is even more concerning is that the route of South Bench Drive lies right where this slide took place. If our city heeds that important last bullet point on page 168, they will realize that putting a major thorough-fare here is going to be hazardous to our slopes and therefore our residents and our city.
Sliverleaf:
Page 349
This study was done while the Silverleaf subdivision was underway. While a slide to this area has not happened, the conclusion was that this slope was only moderately stable and future landslides were definitely a possibility. We see a little more background here to past slides in South Weber as well.
"A site-specific detailed landslide investigation is needed to assess the safety of placing houses on or near pre-existing landslides and marginally stable slopes. The site is within the Davis County Planning Department landslide special-study area (Lowe, 1988c) where detailed landslide studies are recommended (Robison and Lowe, 1993). Pashley and Wiggins (1972) recognized both rotational and flow landslides in the South Weber and Washington Terrace landslide complexes bordering the Weber River northwest of this site. A large rotational slump and earthflow occurred in 1981 northwest of the site (Gill, 1981) in the bluff north of the Weber River. Shallow landsliding northwest and west of this site in 1998 occurred along the Davis- Weber canal (Black, 1999) and above the Cedar Bench subdivision (Solomon, 1999) in South Weber. Flow-type landslides similar to those that likely formed the scallops in the slope south of the site were common elsewhere in the area in 1983 and 1986 (Lowe, 1988d,e; Lowe and others, 1992). All of the above landslides involved failure of Lake Bonneville Weber River delta sediments and demonstrate the susceptibility of these slopes to landsliding."
Recap:
South Weber has had 6 landslides referenced in this study alone since 1983. Other studies refer to additional landslides in this same timeframe. All these studies, as well as our own general plan, state that our south slopes are unstable and in many cases hazardous. A city council member mentioned recently that we need to have another route out of the city - what if there is an earthquake? And yet all of these studies determine that our slopes more than likely will slide in the event of an earthquake, and may even slide without an earthquake! Clearly, a road built on these slopes isn't going to be any help to us. We have been exceedingly cautioned numerous times about any type of excavation or development on our slopes, and I think we would be doing all citizens of South Weber a huge, and potentially dangerous, disservice by not heeding those warnings.
#SWmorethan20
Additional Sources (thanks to Jacqui Layton)
Additional Sources (thanks to Jacqui Layton)
Richard E. Giraud, P.G. and Greg N. McDonald, P.G. References
Black, B.D., 1999, Reconnaissance of a landslide along the Davis-Weber Canal near 1250 East
South Weber Drive, South Weber, Davis County, Utah, in McDonald, G.N., compiler,
Technical reports for 1998, Applied Geology Program: Utah Geological Survey Report
of Investigation 242, p. 36-41.
Earthtec Testing and Engineering, P.C., 2002, Geotechnical study, Highland View Estates
subdivision, South Weber, Utah: Ogden, Utah, unpublished consultant’s report, 13 p.
Giraud, R.E., 2005, Reconnaissance of the 425 East South Weber Drive landslide, South Weber,
Utah: Unpublished Utah Geological Survey Technical Report 05-03, 10 p.
—2006, April 9, 2006, landslide at 1650 East 7687 South, South Weber, Utah: Unpublished
Utah Geological Survey letter to Joseph E. Gertge, South Weber City Mayor, April 14,
2006, 3 p.
Lowe, M., 1988, Natural hazards overlay zone -slope-failure inventory map, Ogden quadrangle:
Weber County Planning Department unpublished map, scale 1:24,000.
Lund, W.R., 1984, Inspection of landslides adjacent to Hill Air Force Base in Davis County,
Utah: Unpublished Utah Geological and Mineral Survey Technical Memorandum, Job
Number 84-09, 1 p.
National Weather Service, 2006, Observed weather reports: Online, <http://www.wrh.noaa.gov/slc/forecast/textproduct.php?pil=CLM&sid=SLC&version=0>, accessed May 8, 2006.
Pashley, E.F., Jr., and Wiggins, R.A., 1972, Landslides of the northern Wasatch Front, in Hilpert,
L.S., editor, Environmental geology of the Wasatch Front, 1971: Utah Geological
Association Publication 1, p. K1-K16.
Ray, I.J., 2006, April 9, 2006, mudslide in South Weber: Sunset, Utah, unpublished Davis and
Weber Counties Canal Company letter to Haven J. Barlow, Barlow Corporation, April 28, 2006, 2 p.
Solomon, B.J., 1999, Reconnaissance of a landslide near the Cedar Bench subdivision, South
Weber, Davis County, Utah, in McDonald, G.N., compiler, Technical reports for 1998,
Applied Geology Program: Utah Geological Survey Report of Investigation 242, p. 42-
49.
Terracon, 2000, Geotechnical engineering report, evaluation of Davis andWeber Canal stations
160 to 470, Davis County, Utah: Draper, Utah, unpublished consultant’s report, 24 p., 3
appendices.
—2005, Slope stability evaluation, Davis and Weber Canal at Highland View Estates, South
Weber, Utah: Draper, Utah, unpublished consultant’s report, 13 p., 4 appendices.
TerraServer USA, 2006, U.S. Geological Survey 1997 and 2003 aerial photographs: Online,
<http://terraserver.microsoft.com/image.aspx?T=4&S=11&Z=12&X=1054&Y=11365&W=1&qs=%7clayton%7cut> , accessed May 5, 2006.
Utah Automated Geographic Reference Center, 2006, National Agriculture Imagery Program
aerial photos: Online, <http://agrc.utah.gov/agrc_sgid/naip.html>, accessed May 5, 2006.
Yonkee, A., and Lowe, M., 2004, Geologic map of the Ogden 7.5-minute quadrangle, Weber and
Davis Counties, Utah: Utah Geological Survey Map 200, 42 p. pamphlet, scale 1:24,000.
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