J.09_2017_12_06_EA_Thurman_I_and_II.pdf

FINAL

ENVIRONMENTAL ASSESSMENT

AND

FINDING OF NO SIGNIFICANT IMPACT:

CHANNEL MAINTENANCE ALTERNATIVES

AT THURMAN I and II ARROYOS IN HATCH, NM, RIO GRANDE CANALIZATION PROJECT

Prepared by:

United States Section, International Boundary and Water Commission

El Paso, Texas

December 6, 2017

COVER SHEET

FINAL Environmental Assessment and Finding of No Significant Impact

Channel Maintenance Alternatives at Thurman I and II Arroyos in

Hatch, NM, Rio Grande Canalization Project

Lead Agency: United States Section, International Boundary and Water Commission

Preferred alternative: Sediment Basins at Thurman I and II Arroyos

Report Designation: Final Environmental Assessment (EA)

Abstract: The USIBWC is considering constructing sediment control projects at Thurman I and II, two ephemeral tributaries of the Rio Grande, located within a portion of the Rio Grande Canalization Project protective levee system in Hatch, Doña Ana County, New Mexico. The USIBWC has the statutory authority to maintain the Rio Grande (Act of June 4, 1936, 49 Stat.

1463, Public Law No. 648 and 22 United States Code 277). USIBWC commissioned a study in 2015 that recommended sediment control structures be built on Thurman I and II arroyos, among others, to trap sediment and assist in the maintenance of the Rio Grande.

The purpose is to construct sediment control structures on Thurman I and II arroyos with the following objectives:

1) Control the inflow of sediment into the Rio Grande mainstem

2) Conduct a pilot study for channel maintenance alternatives

3) Be accessible for maintenance and require little operational costs.

This Environmental Assessment evaluates potential environmental impacts of the No Action Alternative and two alternatives. The Alternative A: No Action – Routine Sediment Excavation does not call for any construction but would require continued routine sediment excavation at the confluence of the arroyos and the Rio Grande. Alternative B: Mesh-Based Sediment Traps proposes to construct mesh and rebar sediment traps where each mesh would trap progressively smaller sediment particles. Alternative C: Sediment Basins is the Preferred Alternative, and calls for the construction of a sediment basin at each arroyo with a concrete end wall. Permits would be required from the U.S. Army Corps of Engineers for dredge and fill of Waters of the United States, per the Clean Water Act Sections 404 and 401.

Potential impacts on natural, cultural, and other resources were evaluated. Mitigation has been proposed for permits for construction. A Finding of No Significant Impact has been prepared for the Preferred Alternative based on a review of the facts and analyses contained in the Environmental Assessment.

Draft Finding of No Significant Impact: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, September 2017 1

FINAL FINDING OF NO SIGNIFICANT IMPACT

Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project

I. LEAD AGENCY: United States Section, International Boundary and Water Commission, United States and Mexico (USIBWC)

II. BACKGROUND

The Rio Grande Canalization Project (RGCP) was authorized by the Act of June 4, 1936, 49 Stat. 1463, Public Law No. 648 to facilitate compliance with the Convention concluded with Mexico on May 21, 1906, (TS 455), providing for the equitable division of waters of the Rio Grande, and to properly regulate and control the water supply for use in the two countries. The Act authorized the construction, operation, and maintenance of the project in accordance with the plan in the Engineering Report of December 14, 1935. The RGCP consists of a narrow river corridor that extends 105.4 miles along the Rio Grande, from below Percha Dam in Sierra County, New Mexico to American Dam in El Paso, Texas. A levee system for flood control extends 57 miles over the west side and 74 miles over the east side of the Rio Grande.

Sediment inflows impact various aspects of the RGCP, including preventing effective operation of dam infrastructure, decreasing the flood conveyance capacity of the RGCP, increasing flood risk to adjoining communities, threatening levee infrastructure, and decreasing the conveyance efficiency of irrigation water along the RGCP to downstream U.S.

and Mexico users. The USIBWC has authorization (22 U.S.C 277) to operate and maintain any projects or works provided for in a treaty entered into with Mexico. USIBWC must maintain the RGCP channel as stipulated in 22 U.S.C 277b, which states that the USIBWC may make improvements to the RGCP, and that "such improvements may include all such works as may be needed to stabilize the Rio Grande" between Percha and American Dam.

In June 2009, the USIBWC signed the Record of Decision for River Management Alternatives for the RGCP (ROD), based on a 2004 Environmental Impact Statement. The ROD committed the USIBWC to continuing to implement its mission of flood control and water deliveries while implementing environmental measures in the long-term management of the river corridor, as well as updating the River Management Plan and conducting studies and investigations to evaluate channel maintenance activities. In October 2015, USIBWC contractors concluded the Channel Maintenance Alternatives (CMAs) and Sediment Transport Study for the RGCP (2015 CMA Study). This 2015 CMA Study analyzed sediment transport and sediment plugs in nine locations throughout the RGCP. In December 2016, USIBWC finalized the River Management Plan (RMP), including Part 4 Channel

Draft Finding of No Significant Impact: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, September 2017 2

Maintenance Plan (USIBWC 2016). The final RMP incorporated results of the 2015 CMA Study. One such recommendation is a conceptual project to construct sediment traps on several arroyos that contribute large amounts of sediment to the RGCP, including Thurman I and II arroyos. USIBWC chose to move forward with the sediment trap concept, using Thurman I and II arroyos as a pilot study for sediment control.

The need is to address sediment input into the Rio Grande, where it causes issues for flood capacity, delivery efficiencies, operations of infrastructure, and levee integrity.

The purpose of this project is to construct sediment control structures on Thurman I and II arroyos with the following objectives:

1) Control the inflow of sediment into the Rio Grande mainstem,

2) Conduct a pilot study for channel maintenance alternatives, and

3) Be accessible for maintenance and require little operational costs.

III. ALTERNATIVE ACTIONS CONSIDERED

The accompanying Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project (Thurman EA), dated December 1, 2017, evaluated potential environmental impacts of the No Action Alternative and two alternatives. The Alternative A: No Action – Routine Sediment Excavation does not call for any construction but would require continued routine sediment excavation at the confluence of the arroyos and the Rio Grande. Alternative B: Mesh-Based Sediment Traps proposes to construct mesh and rebar sediment traps where each mesh would trap progressively smaller sediment particles. Alternative C: Sediment Basins is the Preferred Alternative, and calls for the construction of a sediment basin with a concrete end wall at each arroyo.

IV. NEPA REGULATORY BACKGROUND

Pursuant to National Environmental Policy Act (NEPA) guidance (40 CFR 1500-1508), the President’s Council on Environmental Quality issued regulations for NEPA implementation which included provisions for both the content and procedural aspects of the required NEPA documentation. The Thurman EA, which evaluated the No Action and two alternatives that meet the purpose and need, supports this Finding of No Significant Impact.

V. SUMMARY OF ENVIRONMENTAL CONSEQUENCES OF THE NO

ACTION ALTERNATIVE AND ALTNERATIVE B

The No Action Alternative – Routine Sediment Excavation would require sediment excavation of the sediment that has accumulated in the river channel and the vegetation that has started growing on the sediment bar/islands. No mitigation is anticipated for this action which is covered under USIBWC’s 2017 Biological Opinion and is part of USIBWC’s 2016 River Management Plan. No other environmental impacts are anticipated.

Draft Finding of No Significant Impact: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, September 2017 3

The Alternative B: Mesh-Based Sediment Traps would have similar impacts from the sediment excavation of the river and vegetated sediment bars/islands, in addition to excavation of some of the floodplain. There would be some temporary impacts on noise and air pollution from construction, but these are expected to be minor. No other impacts are anticipated.

VI. SUMMARY OF ENVIRONMENTAL CONSEQUENCES OF THE

PREFERRED ALTERNATIVE

The Alternative C would have similar impacts from the sediment excavation of the river and vegetated sediment bars/islands, in addition to excavation of some of the floodplain. There would be some temporary impacts on noise and air pollution from construction, but these are expected to be minor. The local groundwater levels may be impacted due to the change in hydrology of the arroyo from a fast-moving ephemeral stream to a ponded stream. USIBWC would mitigate for impacts to vegetation and changes in hydrology by creating new riparian habitat, enhancing existing habitat, and creating and protecting an embayment area.

Biological Resources No wetlands would be impacted, since no wetlands were identified in the floodplain in this stretch. Excavation of sediment basins would not impact any vegetation in the floodplain since this area is currently mowed. The proposed endwall location would be slightly upstream of the mouth of the arroyo and would minimize excavation of native vegetation. Wildlife is not anticipated to be directly impacted. This alternative also proposed to remove up to 1.71 acres of vegetation that is growing in the sandbar within the channel; effects are covered under the 2017 Biological Opinion. USIBWC would mitigate for the project, and the sediment basins could create suitable and moist conditions for riparian vegetation along the banks of the sediment basins, as proposed in the preliminary mitigation.

In addition, whenever possible, work would be planned to occur outside of the bird nesting season. If work continues into the bird breeding season the areas proposed for disturbance would be surveyed and avoidance measures followed in order to prevent the inadvertent destruction of nests or eggs.

Cultural Resources USIBWC has extensively surveyed the RGCP for cultural resources. No cultural resources were documented in the project area. Construction from the Preferred Alternative is not expected to adversely affect known archaeological or historical resources. USIBWC would follow standard procedure and best management practices to stop construction work if any cultural resources were found during construction and conduct cultural investigations.

Water Resources Regarding flood control, beneficial impacts are anticipated from the construction of sediment basins, which would hold sediment and prevent it from entering the river, thereby potentially reducing flood capacity and reducing impacts to levees on the opposite bank from the arroyos due to erosive forces. The sediment basin is easier to maintain than Alternative B, but will still require maintenance every several years and a placement site for accumulated sediment.

Draft Finding of No Significant Impact: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, September 2017 4

No impacts to water quality are anticipated. Construction in the Rio Grande channel would likely occur outside of irrigation season when there is little or no water in the river channel.

Construction contractors would be required to have a Stormwater Pollution Prevention Plan in place. Avoidance measures and best management practices would be implemented to avoid impacts to water quality. Implementation of BMP’s would reduce or eliminate erosion and downstream sedimentation and the consequential effects to water quality. Construction would follow stormwater protection permits and water quality certification requirements issued by state agencies.

Although dewatering may be required during construction of the endwalls, the impacts on local groundwater levels from dewatering are anticipated to be negligible. After construction, the sediment basins could create minor changes in local groundwater levels by ponding; this local variability would positively impact proposed mitigation areas by creating more suitable conditions.

The construction of the sediment basins requires rip rap and an endwall. USIBWC would obtain appropriate permits for 0.66 acres of fill of Waters of the U.S., and USIBWC has drafted a preliminary mitigation plan for a total of 2.1 acres, which would require review and approval of the U.S. Army Corps of Engineers.

Environmental Justice Regarding environmental justice, no adverse impacts are anticipated. The construction of the sediment basins does not disproportionately target or affect populations of low-income or minority residents.

VII. MITIGATION AND BEST MANAGEMENT PRACTICES

USIBWC anticipates applying for an individual permit under the Clean Water Act Section 401/404 from the U.S. Army Corps of Engineers for the construction of the sediment basins.

The permit would include a compensatory mitigation plan, which proposes to mitigate 2.1 acres.

The three types of mitigation USIBWC proposes are as follows:

1. Establish onsite riparian areas along each new sediment basin banks by planting native willows. The sediment basins will create moister and more feasible conditions for riparian habitat than are currently present along the stream banks by slowing and pooling water.

2. Enhance existing riparian habitat along the embayment and river banks by removing nonnative vegetation such as saltcedar and planting native willows and cottonwoods.

3. Protect the embayment created after the endwall in constructed as an aquatic habitat pool on the riverside of the endwall.

Best management practices during and after construction would include standard USIBWC measures to protect soil, vegetation, wildlife, cultural resources, water resources, and air

Final Environmental Assessment:

Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project

Prepared By:

United States Section, International Boundary and Water Commission

United States and Mexico

December 6, 2017

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 ii

Contents ACRONYMS AND ABBREVIATIONS ....................................................................................... iv

SECTION 1 BACKGROUND, AND PURPOSE OF/NEED FOR ACTION

1.1 SUMMARY OF PURPOSE AND NEED

1.2 BACKGROUND OF THE RIO GRANDE CANALIZATION PROJECT

1.3 SEDIMENT ACCUMULATION IN RGCP

1.4 CHANNEL MAINTENANCE OF THE RGCP

1.5 PREVIOUS STUDIES FOR CHANNEL MAINTENANCE

1.6 2015 CHANNEL MAINTENANCE ALTERNATIVES AND SEDIMENT

TRANSPORT STUDY

1.7 PURPOSE AND NEED

1.8 PROJECT AREA

1.9 SCOPE OF THE ENVIRONMENTAL REVIEW

SECTION 2 DESCRIPTION OF PROPOSED ALTERNATIVES

2.1 SUMMARY OF ALTERNATIVES EVALUATED

2.2 ALTERNATIVE A: NO ACTION – ROUTINE SEDIMENT EXCAVATION

2.3 ALTERNATIVE B: MESH-BASED SEDIMENT TRAPS

2.4 ALTERNATIVE C: SEDIMENT BASINS – PREFERRED ALTERNATIVE

2.5 SUMMARY COMPARISON OF ENVIRONMENTAL CONSEQUENCES

SECTION 3 CURRENT CONDITIONS AND ENVIRONMENTAL CONSEQUENCES

3.1 BIOLOGICAL RESOURCES

3.1.1 Vegetation and Wetlands

3.1.2 Wildlife

3.1.3 Threatened and Endangered Species

3.2 CULTURAL RESOURCES

3.3 WATER RESOURCES

3.3.1 Flood Control

3.3.2 Water Quality

3.3.3 Groundwater

3.3.4 Waters of the United States

3.4 Environmental Justice

3.5 OTHER FACTORS CONSIDERED AND ELIMINATED FROM ANALYSIS

3.6 CUMULATIVE IMPACTS

3.6.1 Addressing Sediment Input

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 iii

3.6.2 Other Projects

3.7 UNAVOIDABLE ADVERSE IMPACTS, AND IRRETRIEVABLE COMMITMENTS

OF RESOURCES

SECTION 4 MITIGATION MEASURES

4.1 MITIGATION PLAN

SECTION 5 PUBLIC INVOLVEMENT

5.1 AGENCY COORDINATION

5.2 PUBLIC INFORMATION AND REVIEW

SECTION 6 LIST OF PREPARERS

SECTION 7 REFERENCES

Appendix A Project Designs (PreFinal)

Appendix B Photos of Project Area

Appendix C Distribution and Coordination

Appendix D Draft Environmental Assessment Review Comments and Changes Made to the Draft EA 92

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 iv

ACRONYMS AND ABBREVIATIONS

APE Area of potential effect

BNSF Burlington Northern Santa Fe Railroad

CFR Code of Federal Regulations

CEQ Commission on Environmental Quality

CY Cubic yard

EA Environmental Assessment

EIS Environmental Impact Statement

ESA Endangered Species Act

FEM Field Environmental Monitor

FEMA Federal Emergency Management Agency

MBTA Migratory Bird Treaty Act

NEPA National Environmental Policy Act

NHPA National Historic Preservation Act

NMED New Mexico Environment Department

NMDGF New Mexico Department of Game and Fish

NMHPD New Mexico Historic Preservation Division

RGCP Rio Grande Canalization Project

ROD Record of Decision

SEA Supplemental Environmental Assessment

SHPO State Historical Preservation Officer

T&E threatened and endangered

U.S. United States

USACE U.S. Army Corps of Engineers

USEPA U.S. Environmental Protection Agency

USFWS U.S. Fish and Wildlife Service

USIBWC International Boundary and Water Commission, United States Section

WOUS Waters of the United States

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 1

SECTION 1 BACKGROUND, AND PURPOSE OF/NEED FOR ACTION

1.1 SUMMARY OF PURPOSE AND NEED

Sediment input into the Rio Grande impacts flood control and water delivery infrastructure such as levees and dams. The purpose of the action analyzed in this Environmental Assessment (EA) is to:

1) Address and control sediment inflow from Thurman I and II arroyos (Figures 1-2 and 1-

3) into the Rio Grande main stem,

2) Conduct a pilot study for channel maintenance alternatives that could be replicated in other areas, and

3) Facilitate maintenance of the Rio Grande sediment input and minimize operational costs within the Rio Grande Canalization Project.

The Purpose and Need is discussed further in Section 1.6 after several sections of background information related to the project.

1.2 BACKGROUND OF THE RIO GRANDE CANALIZATION PROJECT

The Rio Grande Canalization Project (RGCP) consists of a narrow river corridor that extends

105.4 miles along the Rio Grande, from below Percha Dam in Sierra County, New Mexico to American Dam in El Paso, Texas (Figure 1-1). A levee system for flood control extends 57 miles over the west side and 74 miles over the east side of the Rio Grande (USIBWC 2004b).

The RGCP was authorized by the Act of June 4, 1936, 49 Stat. 1463, Public Law No. 648 to a) facilitate compliance with the Convention concluded with Mexico on May 21, 1906 (TS 455) providing for the equitable division of waters of the Rio Grande, and b) properly regulate and control the water supply for use in the two countries. The Act authorized the International Boundary and Water Commission, United States Section (USIBWC) to construct, operate, and maintain the RGCP in accordance with the plan in the Engineering Report of December 14, 1935, which covers the following engineering works to implement the 1906 Convention:

1) construction of American Dam and Canal,

2) the acquisition of the right of way for the river channel and adjoining floodways,

3) improvement of the alignment and efficiency of the river channel conveyance of deliveries to Mexico, pursuant to the 1906 Convention, as well as conveyance of deliveries to the United States Bureau of Reclamation (USBR) Rio Grande Project in the Mesilla and Rincon valleys of New Mexico and the El Paso valley of Texas,

4) protection against a flow equal to the largest flood of record in this reach (USIBWC 1994;

IBC 1935), specifically “a channel designed to carry the ordinary flows of the river, and a flood channel, to be defined by adequate and proper levees, designed to carry the estimated maximum flood flows”(IBC 1935), and

5) operation and maintenance of the RGCP, specifically “in order to prevent meandering of the controlled flow, it is proposed to perform the excavation by suction dredges, discharges the

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 2 excavated material in such areas” (IBC 1935).

1.3 SEDIMENT ACCUMULATION IN RGCP

Sediment inflows impact various aspects of the RGCP. For example, sediment deposits:

• decrease the flood conveyance capacity of the RGCP and increase flood risk to adjoining communities (USACE 1996; USIBWC 2004b; USIBWC 2015);

• decrease the conveyance efficiency of irrigation water along the RGCP to downstream U.S. stakeholders such as the Elephant Butte Irrigation District (EBID) and El Paso County Water Improvement District No. 1 (EPCWID No. 1), and Mexico (Riada 2009;

USIBWC 2015);

• may be responsible for increased seepage of irrigation water released from the upstream Caballo reservoir into the underlying aquifer resulting in decreased surface flow available downstream, particularly in drier years (USIBWC 2013);

• create sediment blockage of irrigation return flows which increases landside ground water table elevations, resulting in increased salinity for farming operations;

• threaten floodplain and levee infrastructure (such as on the opposite banks from incoming arroyos, where sediment deposits at arroyo mouths cause the river’s flowpath to change around sediment deposits, eroding the opposite bank and potentially threatening the integrity of the levee opposite the arroyo via underseepage and erosion)

(USIBWC 2016);

• create islands which exacerbate the above issues (Riada 2009); and

• accumulate at flood control and water delivery infrastructure, such as Mesilla and

American Dams, preventing efficient and effective operation of the infrastructure (USIBWC 2004b).

1.4 CHANNEL MAINTENANCE OF THE RGCP

The USIBWC has authorization (22 U.S.C 277) to operate and maintain any projects or works provided for in a treaty entered into with Mexico. USIBWC must maintain the RGCP channel as stipulated in 22 U.S.C 277b, which states that the USIBWC may make improvements to the RGCP, and that "such improvements may include all such works as may be needed to stabilize the Rio Grande" between Percha and American Dam.

Since the RGCP was completed in the 1940s, the USIBWC has conducted channel maintenance activities as part of its statutory requirements to ensure efficient deliveries and to contain and convey flood flows. The USIBWC’s routine channel maintenance activities conducted in the RGCP prior to 2009 included dredging or excavating along the RGCP to control sediment below dam structures; stabilizing banks; removing obstructions such as debris, sediment plugs, or gravel deposits; and maintaining arroyos that act as flood conveyance. The volumes of sediment removed from the channel and tributaries each year has varied widely. Prior to 1990, between 40,000 and 450,000 cubic yards (CY) of sediment were removed from the main channel each year to maintain normal and flood flow capacities (USIBWC 2000). Quantities after 1990 also varied highly, but ranged from 20,000 to 235,000 CY.

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 3

In 2004, the USIBWC published the final Environmental Impact Statement (EIS) for River Management Alternatives for the Rio Grande Canalization Project in August 2004 (USIBWC 2004b), which evaluated options for long-term management of the river corridor, including habitat restoration, vegetation management, channel maintenance, and flood control improvements. The Record of Decision (ROD) was signed in June 2009 by USIBWC Commissioner Bill Ruth.

(USIBWC 2009). The ROD committed the USIBWC to continuing to implement its mission of flood control and water deliveries while implementing environmental measures in the long-term management of the river corridor. The 2009 ROD required the USIBWC to improve river management by updating the river management plan; establishing a data collection and evaluation program for channel maintenance; updating and evaluating river cross section data every four to five years and updating hydraulic models; conducting studies and investigations to evaluate channel maintenance activities and levee protection; investigate the overall necessity of channel dredging through monitoring and modeling; implementing restoration sites in the floodplain;

conducting in‐channel enhancements at arroyos and an inset floodplain; and using adaptive management strategies.

From 2009 to 2013, after the signing of the ROD, USIBWC stopped almost all channel maintenance with the exception of sediment excavation at the gates of American Dam. Lack of channel maintenance and low flows caused by drought conditions led to numerous sediment plugs and issues that required the USIBWC's attention. In December of 2013, USIBWC drafted a preliminary working draft of this Channel Maintenance Plan. Per the ROD, the USIBWC worked with irrigation districts and stakeholders on the channel maintenance plan from 2013 to 2016, during which time USIBWC used the preliminary working draft for channel maintenance implementation. In December 2016, USIBWC finalized the River Management Plan, including Part 4 Channel Maintenance Plan (USIBWC 2016). The final plan incorporated results of studies discussed in the next section.

1.5 PREVIOUS STUDIES FOR CHANNEL MAINTENANCE

In 1996, the USACE conducted a detailed hydrologic, hydraulic and sediment analysis of the RGCP. This study included HEC-1 modeling for the approximately 900-square mile drainage area.

A HEC-2 hydraulic model computed water surface profiles. Using the Modified Universal Soil Loss Equation (MUSLE) to estimate the wash load and the HEC-6 sediment transport model for the bed load, the total sediment load was obtained for 20 arroyo basins along the RGCP for the 2-, 5-, 10-, 25-, 50- and 100-year storm events and the average annual storm (USACE 1996).

In 2003, Parsons created a HEC-RAS model for the Environmental Impact Statement (Parsons 2004b). In October 2005, the report study Upper Rio Grande Water Operations Model FLO-2D Model Development Below Caballo Dam (URGWOM) was prepared for the USIBWC and USACE using FLO-2D Model Development (USACE 2005). This model evaluated and updated the 1996 HEC-1 model as well as the 2003 Parsons HEC-RAS model. The 100-year floodplains were mapped based on FLO-2D simulations. This 2005 study also evaluated the 1996 sediment studies and recommended adjustment factors.

A 2009 study (Riada Engineering, Inc. 2009) determined that channel maintenance activities to

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 4 remove individual sediment plugs and islands have minimal impact on the flood maximum water surface elevations and irrigation in terms of volume and arrival of the irrigation releases. In addition, the study found that the lifespan of such expensive maintenance activities is relatively short (ranging from months to 1.7 years). However, the same study also stated that the cumulative effect of the formation of islands and sediment plugs in the channel can be more pronounced than the impact of individual islands and plugs. In response to a general 100‐year storm over the entire basin where all of the arroyos create sediment plugs simultaneously in the channel, the maximum flood water surface can increase up to two feet in specific locations. The same study also showed that flood water surface elevations could increase up to two feet in specific locations as a result of sediment buildup (Riada Engineering, Inc. 2009).

Similarly, the 2007 USACE study stated that “the profile and sediment continuity data suggest that there may be more hydraulic capacity in the RGCP than was initially designed, and extensive removal of sediment from the river may, therefore, not be necessary to maintain conveyance capacity, at least in portions of the reach” (USACE 2007, p 6.18).

Similarly, the 2007 USACE study stated that “the profile and sediment continuity data suggest that there may be more hydraulic capacity in the RGCP than was initially designed, and extensive removal of sediment from the river may, therefore, not be necessary to maintain conveyance capacity, at least in portions of the reach” (USACE 2007, p 6.18).

It must be noted that previous studies have assumed a dynamic equilibrium of sediment inflow and outflow along the RGCP. However, individual storm events can bring in more sediment from the tributary arroyos that, in the absence of efficient transport downstream and removal, will accumulate within the RGCP. Under flooding conditions, the resulting water surface elevation increase will compromise levee freeboard and increase the risk of flooding to adjoining communities. USIBWC verified this in 2013 using HEC-RAS modeling at the Montoya Drain outfall location.

The USACE 2007 report also indicated that sediment delivery events “have significant local impacts on the mainstem Rio Grande, primarily in the portions of the RGCP upstream from Selden Canyon” where channel blockage occurs by coarse-grains tributary fans, causing upstream backwater, overbank flows, and flow conveyance losses. In addition, the sediment may damage existing bank protection or lead to lateral migration of the river, both causing “potential threats to the integrity of the levee system or other channel margin infrastructure such as bridges and siphons” (USACE 2007, p 6.9).

In 2009, the USACE analyzed the restoration potential at 30 restorations sites using the 2007 model (USACE 2009). The study included a sediment continuity analysis to evaluate the potential for aggradation and degradation for reservoir operations. A cumulative effects analysis was performed to evaluate the effects of all proposed restoration activities on water surface elevations, flood wave attenuation and timing, channel stability and other factors (Unnikrishna 2012). In 2013, URS developed a smaller 50-foot grid FLO-2D model for eleven (11) arroyos contributing from the east in the Vinton Bridge to Borderland Bridge reach. Arroyo flows were calculated using a HEC-HMS model. The results were used to design approximately six (6) miles of levee improvement projects

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 5 in the Canutillo, Texas area (URS 2013).

In 2013, Tetra Tech completed a Preliminary Water Budget Study that determined the extent to which the amount of Rio Grande Project water would be available for diversion to US irrigators and for delivery to Mexico under different release scenarios compared to the actual 2012 release.

Hypothetical normal release (end March to mid September) and delayed release (end May to mid September) scenarios were explored (USIBWC 2013). Part of this work was to update the 2007 FLO-2D and HEC-RAS models to estimate the 2012 seepage.

Under irrigation flow conditions, hydraulic modeling studies have indicated increased seepage in the ongoing drought years as compared to the previous normal flow years (USIBWC 2013).

Seepage will increase further with the accumulation of sediment in the main channel, reducing the efficiency of irrigation water deliveries during a time of water shortage.

Therefore, accumulation of sediment has an adverse localized impact during both high flow and low flow conditions. The ROD contemplated addressing some channel maintenance issues with new approaches and adaptive management. Although the ROD listed the cessation of dredging as a channel restoration approach, it did not rule out dredging and pre-ROD maintenance activities altogether. The ROD listed channel management and maintenance activities, including dredging, island removal, arroyo realignment and arroyo mouth management, along with other more non-traditional activities such as bank destabilization.

From September 2014 to October 2015, USIBWC contractors conducted a Channel Maintenance Alternatives (CMAs) and Sediment Transport Study for the RGCP (henceforth referred to as the “2015 CMA Study” (USIBWC 2015).

The 2015 CMA Study is discussed in more detail in the following section.

1.6 2015 CHANNEL MAINTENANCE ALTERNATIVES AND SEDIMENT

TRANSPORT STUDY

In September 2014, the USIBWC contracted Tetra Tech to undertake the Channel Maintenance Alternatives and Sediment Transport Study to evaluate sedimentation issues along the RGCP at nine representative problem locations, listed in Table 4-5. Objectives of the study included:

Update the base HEC-RAS model with additional components such as the latest levee;

information and changed site conditions, updated cross section survey data, and 2011 LIDAR data;

Conduct additional hydraulic modeling to provide quantitative measures to support the stated goals of the ROD;

Conduct sediment transport analyses to study sediment aggradation/degradation along the RGCP under normal operations and in response to storm events to obtain and understanding of required operations and maintenance consistent with the ROD;

Analyze impacts of sediment plugs on water surface elevations at particular locations;

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 6

Analyze impacts of channel maintenance, such as island removal and sediment excavation, and other representative site-specific characteristics such as an existing vortex weir, dams, islands, arroyos, and drains;

Propose and analyze alternatives to sediment removal;

Evaluate sediment removal and non-sediment removal channel maintenance options using a set of evaluation criteria; and

Recommend the top scoring channel maintenance alternatives for implementation at each of the nine representative problem locations.

The 2015 CMA Study analyzed sediment transport and aggradation/degradation of the river, and the study concurred with the previous studies regarding predicted and observed aggradation and degradation patterns. The study did indicate that localized sediment buildup was an issue and that addressing the sedimentation would result in lower predicted water surface elevations (Tetra Tech 2015). Figure 4-2 compares the Pre-Canalization, 1943 design and 2004 thalweg profiles of the RGCP, as well as the changes in elevation between the Pre-Canalization and 1943 profiles (green line) and between the 1943 profile and the 2004 profile (red line). The study documented the following aggradation and degradation in the RGCP since 1943:

From Percha Dam to the Hatch Siphon - historically degraded between 4 and 6 feet

From the Hatch Siphon to the head of Selden Canyon - Immediately downstream of the Hatch Siphon, the channel has historically degraded about 10 feet. For the remainder of the upper part of the subreach, the degradation reduces from about 6 feet in the upstream end to about 1 foot upstream of the Rincon Siphon. Downstream of the Rincon Siphon, there has been about 9 feet of degradation, but the degradation diminishes in the downstream direction to about 2 feet. Upstream of Bignell Arroyo there has been about 2 feet of aggradation

From the head of Selden Canyon to Leasburg Diversion Dam - There are no comparative thalweg data for this subreach, but under low-flow conditions the bed of the channel is braided and appears to be mildly aggradational.

From Picacho Bridge to the Mesilla Diversion Dam - 2 to 3 feet of historical degradation from the Mesilla Diversion Dam to the Vinton Bridge - up to 8 feet of historical degradation downstream of the Mesilla Diversion Dam, but the amount of degradation diminishes in the downstream direction to about 1 foot from the Vinton Bridge to the American Diversion Dam - up to 2 feet of aggradation

Results from the study are documented in the October 2015 final report (Tetra Tech 2015) and provide a suite of alternatives to reduce or minimize sediment issues. The report identified the most efficient, sustainable, and environmentally beneficial alternatives, both sediment removal and non-removal. The study evaluated five channel maintenance alternatives (CMAs) at each of the nine problem locations, including three classified as sediment removal alternatives (short, long, and localized excavation scenarios) and two that were classified as non-sediment removal alternatives and varied by problem location. The study included field reconnaissance, cross section surveying, Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 7 steady-state hydraulic modeling of the existing conditions and with CMAs, sediment transport modeling of the problem locations, and evaluation of CMAs.

Non-sediment removal CMAs considered under the study included:

Vortex weir

Arroyo sediment traps

Island destabilization/ vegetation removal

Siphon modifications

Low-elevation spur dikes

Dam gate automation

Sluiceway and check structures

Rip rap

Alternatives were evaluated using the following criteria:

reduction in water-surface elevation along the modeled reach, reduced levee freeboard encroachments, groundwater benefits, which include the benefit of increased groundwater levels in the vicinity of restoration sites as well as reduced groundwater levels elsewhere, particularly at drains, reduction in aggradation and downstream sediment loading, improved irrigation drain return flows, durability of the alternative, restoration benefits, in addition to benefits associated with increased groundwater levels, and additional site-specific benefits.

The costs and consequences considered in assessing the alternatives included:

annualized total cost of the alternative based on the up-front construction cost and projected

O&M costs, increases to water-surface elevation along the modeled reach, levee freeboard encroachments, groundwater consequences, which include the consequence of decreased groundwater levels in the vicinity of restoration sites as well as increased groundwater levels elsewhere, increases to aggradation and downstream sediment loading, increased bank erosion potential, restoration consequences, in addition to those consequences associated with increased groundwater levels, and additional site-specific consequences.

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 8

Table 1‐1 Problem Areas evaluated in the 2015 CMA study

Problem Location Representation River Mile Range (miles upstream of American Dam) Length (miles)

1. Tierra Blanca Creek to Sibley Arroyo Vortex Weir 97.8 ‐ 100.1 2.3

2. Salem Bridge to Placitas Arroyo Arroyos and Islands 84.4 ‐ 88.2 3.8

3. Rincon Siphon A Restoration Site to Rincon Siphon

Restoration Sites and Siphon 82 ‐ 82.8

0.8

4. Rincon Arroyo to Bignell Arroyo Arroyos and Islands 75.5 ‐ 79 3.5

5. Rock Canyon to 1.4 mi below Rincon/Tonuco Drain Confluence

Drain and Mouth of Selden Canyon

68.9 ‐ 71.8 2.9

6. Picacho Drain to below Mesilla Dam Drain, Canals, and Dam 38.8 ‐ 41.2 2.4

7. East Drain to below Vinton Bridge Drain and Arroyo 14.8 ‐ 16.6 1.8

8. Upstream of Country Club Bridge to NeMexas Siphon

No Inputs, Bridge, Populated Area, Levee Encroachments

7.1 ‐ 8.6 1.5

9. Montoya Drain to American Dam Drain, Dam 0 ‐ 2.7 2.7

Figure 1‐1. Pre‐Canalization, 1943 design and 2004 thalweg profiles of the RGCP. (From 2015 CMA Study Fig 2)

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 9

1.7 PURPOSE AND NEED

The 2015 CMA Study recommended arroyo sediment traps be constructed on a number of arroyos in the north part of the RGCP (Tierra Blanca, Sibley, Placitas, Garcia, Canutillo area) as a means to control the sediment input and an alternative to excavating sediment from the main channel of the river. USIBWC evaluated the conceptual plans for proposed sediment traps and based on a number of factors, including small scale and feasibility, USIBWC selected the Thurman I and II Arroyos to implement pilot projects for channel maintenance alternatives. Out of the recommended arroyo traps, Thurman I and II arroyos generated the smallest sediment yield (3,194 cubic yards (CY) (USACE 2007; USIBWC 2015)). Construction was deemed feasible because these were within USIBWC property, were not impacted by future USIBWC levee improvement projects, and preliminary review showed no anticipated impacts to endangered species. The USIBWC prepared this EA to analyze environmental impacts for these pilot projects at Thurman I and II Arroyos.

The purpose of the action is to:

4) Address and control sediment inflow from Thurman I and II arroyos into the Rio Grande main stem,

5) Conduct a pilot study for channel maintenance alternatives that could be replicated in other areas, and

6) Facilitate maintenance of the Rio Grande sediment input and minimize operational costs.

1.8 PROJECT AREA

The Project Area covered under this EA is the immediate vicinity of Thurman I and II Arroyos in Hatch, New Mexico. Figure 1-2 shows the vicinity, and Figure 1-3 shows the Project Area.

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 10

Figure 1‐2 Vicinity Map of the Rio Grande Canalization Project and the Thurman I and II Project Area

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 11

Figure 1‐3 Local Vicinity Map of the Rio Grande Canalization Project and the Thurman I and II Project Area

Figure 1‐4. Project Area of Thurman I and II Arroyos.

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 12

1.9 SCOPE OF THE ENVIRONMENTAL REVIEW

Federal agencies are required to take into consideration the environmental consequences of proposed and alternative actions in the decision-making process under the National Environmental Policy Act (NEPA) of 1969, as amended. The USIBWC regulations for implementing NEPA are specified in Operational Procedures for Implementing Section 102 of the National Environmental Policy Act of 1969, Other Laws Pertaining to Specifics Aspects of the Environment and Applicable Executive Orders (46 FR 44083, September 2, 1981). These federal regulations establish both the administrative process and substantive scope of the environmental impact evaluation designed to ensure that deciding authorities have a proper understanding of the potential environmental consequences of a contemplated course of action.

This EA identifies and evaluates the potential environmental consequences that may result from implementation of three alternatives:

1. Alternative A: No Action – Routine Sediment Excavation

2. Alternative B: Mesh-Based Sediment Traps

3. Alternative C: Sediment Basins – Preferred Alternative.

The following resource areas are analyzed for potential environmental consequences:

biological resources (vegetation and habitat, wildlife, and threatened and endangered species), cultural resources, water resources (flood control, water quality, groundwater, and waters of the U.S.), community resources (environmental justice and recreation), and environmental health (air quality and noise pollution).

Analyses of environmental resources for the affected environment and environmental consequences are based on a potential impact corridor in Hatch, NM. Analyses of environmental consequences also include potential indirect impacts to the river corridor and the region depending on the resource and its relationship to the preferred alternative and the no action alternative.

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 13

SECTION 2 DESCRIPTION OF PROPOSED ALTERNATIVES

2.1 SUMMARY OF ALTERNATIVES EVALUATED

This EA evaluates three alternatives, which are discussed below and summarized in Table 2-1:

1. Alternative A: No Action – Routine Sediment Excavation

2. Alternative B: Mesh-Based Sediment Traps

3. Alternative C: Sediment Basins – Preferred Alternative.

Table 2‐1. Summary of Alternatives Evaluated in this EA

Name Description Advantages Disadvantages Cost

Alternative A: No Action – Routine Sediment Excavation

Status quo

No construction and no land acquisition

Continue routine sediment excavation at the confluences of arroyos and Rio Grande

No construction or acquisition cost

Incurs costs for routine sediment excavation

Coordination required with USACE for excavation work within Waters of the U.S.

$389,2001

Alternative B:

Mesh‐Based Sediment Traps

Construct a series of mesh and rebar traps that catch coarsest material in upstream trap and progressively finer material downstream

Debris rack at the upstream entrance to capture floating debris

Lowest trap would have an embayment that could prove habitat benefits

Allows arroyo flows to continue

Potential for habitat benefits at embayment

Mesh and rebar may not withstand forces from large rocks in arroyo flows

Permit from USACE required for work within Waters of the U.S.

Requires excavation of the arroyo to create the capacity to store the required volume of sediment during tributary flooding events

$721,1082

Alternative C:

Sediment Basins

Construct a sediment basin by deepening and widening each arroyo channel

Construct concrete end wall

Place scour protection at the upstream and downstream ends of the endwall

Allows high arroyo flow to continue

Efficient sediment trapping

Easy to maintain

Resists scour potential

Permit from USACE required for work within Waters of the U.S.

Initial excavation volume

Initial construction cost

Requires excavation of the arroyo to create the capacity to store the required volume of sediment during tributary flooding events

$2.7 million3

1 – Total annualized cost for Long Excavation of Problem Area 2 from USIBWC 2015

2 – Total Construction Costs for Problem Area 2 from USIBWC 2015 (includes costs for trap on Placitas Arroyo). However, this is only a partial cost. Alternative B Mesh Based Traps, were not designed to capture all material. This would allow for the fine material to find its way to the Rio Grande. Therefore, a partial/full cost of Alternative A No Action would still need to be added to Alternative B.

3 –Draft Opinion of Probable Cost dated May 2017 (USIBWC 2017)

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 14

2.2 ALTERNATIVE A: NO ACTION – ROUTINE SEDIMENT EXCAVATION

Under Alternative A, the No Action Alternative – Routine Sediment Excavation, USIBWC would continue routine sediment excavation at the confluences of the arroyos and the Rio Grande. This Alternative, which does not call for any construction, maintains the status quo, as documented in the 2016 River Management Plan (USIBWC 2016), which states that at the Thurman arroyos USIBWC will “Relocate sediment material from the arroyo mouth to the opposite river bank to prevent further erosion. Place rip‐rap along riverbank.” USIBWC anticipates removing an estimated 8,340 cubic yards (CY) from Thurman I and II Arroyos by 2019. In Fiscal Year 2007, the USIBWC removed 7,250 CY of sediment and placed 10,500 CY of rip rap.

Figure 2‐1. Area of routine sediment excavation at Thurman I under Alternative B ‐ No Action (modified from USIBWC 2017b)

Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 6, 2017 15

Figure 2‐2. Area of routine sediment excavation at Thurman II under Alternative B ‐ No Action (modified from USIBWC 2017b)

2.3 ALTERNATIVE B: MESH-BASED SEDIMENT TRAPS

In October 2015, Tetra Tech completed the final report, Channel Maintenance Alternatives and Sediment Transport Study for the Rio Grande Canalization Project (USIBWC 2015), which recommended a conceptual project to construct arroyo sediment traps that would alleviate sediment accumulation at the mouth of arroyos in the Rio Grande by reducing coarse-grained sediment supply into the river. The sediment traps are designed to have a trapping volume that exceeds the average annual bed-load yield from the tributaries. The Alternative B: Mesh-Based Sediment Traps includes:

Construction of a series of mesh and rebar traps that catch coarsest material in the upstream trap and progressively finer material toward the mouth

Installation of a debris rack at the upstream entrance to capture floating debris An embayment area at the lowest trap that could prove habitat benefits Excavation into the floodplain to obtain the required volume.

Alternative B includes the sediment excavation in the No Action and also would install a series of trapping features constructed with rebar and wire screens with progressively finer mesh openings in the downstream…