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NEW MEXICO NEW MODEL CANAL PRELIMINARY ENGINEERING ASSESSMENT Introduction The following report documents a preliminary engineering assessment and alternatives for improvements to the New Mexico New Model Canal. The project is located within Virden, New Mexico and the surrounding area. The canal begins approximately 2 miles upstream of Virden and extends along the south side of the Gila River and into Arizona. The project is approximately 4.5 miles long. Water is diverted from the Gila River and delivered to irrigated cropland within the Virden Valley south of the river. The New Mexico New Model Canal serves 315 acres in New Mexico and another 1,728 acres in Arizona.
Project Location. (Source: USGS 7.5 Minute Series Map, Canador Peak, NM, 1990.) Note: Lower portion of project is found on the adjoining map west of the area shown (i.e., USGS 7.5 Minute Quadrangle, Duncan, AZ). The current (New Mexico) infrastructure includes a river diversion dam and headgate, three blow-off (cleanout and river return) structures with gates, metering gages near the upper and lower ends, approximately 24,000 feet (4.5 miles) of concrete-lined or unlined canal, one HDPE
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pipe at an arroyo crossing, and multiple outlets. A drawing/map summarizing the project is shown in Appendix A. The scope of this engineering assessment is to summarize modifications for improving the performance of the existing system. The proposed improvements consist of installing a water transmission pipeline within the existing canal with new outlets and water meters for individual users, and improving the associated infrastructure. Existing Conditions and Design Challenges The open unlined portion of the canal in current operation creates long-term concerns with maintenance (particularly in heavy vegetation), stability on slopes, sediment capture in some areas, and loss of water due to infiltration, evaporation, and plant uptake. The lined portion of the canal has deteriorated over time, and a portion of this recently failed (see photo above). The U.S. Department of Agriculture, Natural Resources Conservation Services (NRCS) soil survey maps indicate that the Virden Valley contains gravelly and sandy loam soils along the upper perimeter areas next to rough broken land, and silty clay loam in low-lying areas. The canal is positioned along the south side of the valley and passes through several areas containing relatively permeable (gravelly or sandy) soils. The U.S. Geological Survey data for indicates that during the period of record (1932-2012), the Gila River near Virden had an average annual flow ranging from 43.1 cubic feet per second (cfs) to 640.5 cfs, with the maximum recorded peak flow estimated at 58,700 cfs. The river diversion includes a concrete weir across the main river channel and a canal inlet structure with a trash rack and overflow. The overflow structures that return excess water and flush sediments from the upper canal appear to be in working order, although sediment removal and other maintenance is needed after large river flood flows.
Failure in lined canal section (September, 2013).
30-inch I.D. HDPE pipe crossing at arroyo.
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Engineering challenges associated with the pipeline design and installation include:
Minimizing routine and long-term maintenance created by sediment deposition; and Constructing the new system within budget limitations.
Rehabilitation Alternatives To reduce water loss, the canal could be either lined or retrofitted with a pipeline. Although various types of liners would reduce water loss, a pipeline is preferred by the canal owners/operators to best meet the long-term needs and goals. Table 1 describes and compares some common pipe materials. Based on Portages onsite visits and discussions with the project stakeholders, two pipeline alternatives have been selected for presentation in this preliminary engineering assessment. Conceptual design drawings, depicting examples of the various system components, are shown in Appendix B.
Table 1. Pipe Materials Comparison Material Description Advantages Disadvantages
Steel Carbon steel pipe with welded end joints.
Strong, capable of withstanding very high pressures. Leak-free joints.
Corrosion protection needed to extend design life; this may consist of coatings, cathodic protection, pipe wrap, or a combination of these. Relatively high cost. Heavy equipment needed for installation.
Corrugated Metal Pipe (CMP)
Ribbed galvanized steel pipe with sealed end connections.
Commonly used, readily available materials.
Hydraulically rough, may need to use larger size to obtain similar performance as smoother pipe materials. Moderately heavy equipment needed for installation. Joints may leak.
High Density Polyethylene (HDPE)
Thick-walled HDPE plastic pipe with thermally welded end joints.
Withstands moderately high pressures, flexible, hydraulically smooth, high abrasion resistance, tough and non-corrodible material, leak-free joints.
Specialized equipment and crews needed for thermal welding. Moderately heavy equipment needed for installation.
Dual-wall High Density Polyethylene
Smooth inside, corrugated outside HDPE plastic pipe with sealed end connections.
Lightweight, easy installation, flexible, hydraulically smooth, tough and non-corrodible material.
Relatively thin interior walls possibly subject to tearing or abrasion by sharp objects. Joints may leak.
Polyvinyl Chloride (PVC)
PVC plastic pipe with sealed end connections.
Hydraulically smooth, non-corrodible material, easy installation.
Generally smaller sizes. Stiffer material, possibly subject to damage by impact, long bending radius needed. Joints may leak.
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Alternative Cost Estimates Cost estimates for two alternatives are detailed in Appendix C. All cost estimates are based on the following assumptions:
Alternatives presented include no improvements to the river diversion. Pipe sizes selected for presentation in this assessment are based on existing infrastructure
including a short section of 30-inch inside diameter HDPE pipe at an arroyo crossing, capable of transmitting the maximum flow at that location.
The type of pipe shown in the cost estimates is continuous HDPE (with welded joints). All improvements will be made during the irrigation off-season, when surface water and
groundwater levels are low and the chance of a flood event is minimal. Unit prices are based on Portages experience with similar work items on recent projects,
vendor-provided costs, and construction cost data from published sources. Costs include a 15% contingency, to account for price variations and other unknowns.
The table below provides a cost comparison of two alternatives.
Table 2. Alternatives and Costs Alternative Description Estimated Cost ($K)
1 36 Diameter HDPE DR26 water transmission pipeline. 3,793 2 42 Diameter HDPE DR26 water transmission pipeline. 4,777
The two alternatives shown demonstrate the cost difference between two pipe sizes for the assumptions listed above. Table 1 shows a few examples of common pipe materials, but there is a much broader range of pipes, wall thicknesses, joints types, fittings, and other design variables to consider each with cost implications to the overall project. Summary, Discussion, and Limitations As described above, the system rehabilitation presented herein consists of installation of a permanent pipeline replacement to the currently open canal. The engineering design process will need to evaluate various alternative pipeline materials and sizes to determine the most cost effective combination that best meets the system rehabilitation needs. The conceptual designs shown herein are based on readily available data and limited measurements. Complete surveying and mapping of the project site will be necessary to develop further designs. The costs presented in this report are preliminary, and may not represent final construction costs resulting from a complete engineering design.
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References New Mexico Arizona Water Settlements Act (AWSA) Tier 2 Final Proposals, Sunset / New Mexico New Model Pipeline Application, website: http://nmawsa.org/library/AWSA-Proposals%20Home%20Page/tier-2-final-proposals/tier-2-final-proposals. U.S. Department of Agriculture, Natural Resources Conservation Service, Web Soil Survey, website: http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx. U.S. Geological Survey, National Water Information System: Web Interface, Stream Gage Data for Gila River Below Blue Creek, Near Virden, NM, website: http://waterdata.usgs.gov/nm/nwis/uv?site_no=09432000.
PROJECT SUMMARY MAP
CONCEPTUAL DESIGN DRAWINGS
NEW MEXICO NEW MODEL CANAL
PROJECT COST ESTIMATE Subtotal w/ Contingency
ALTERNATIVE 1 TOTAL ESTIMATE: 3,297,842$ 3,792,518$
1. The project begins below the river diversion and extends to the Arizona border.
2. Water transmission pipe is 36-inch diameter HDPE DR26 (81 psi) pipe.
3. Water transmission pip