J.10_2018_05_02_Mitigation_Plan_Thurman_I_and_II.pdf

RIPARIAN HABITAT COMPENSATORY MITIGATION PLAN

FOR

SEDIMENT BASINS AT THURMAN I AND II ARROYOS

DONA ANA COUNTY, NEW MEXICO

UNITED STATES INTERNATIONAL BOUNDARY

AND

WATER COMMISSION

USACE PERMIT APPLICATION NUMBER:

SPA-2018-00084-LCO

MAY 2, 2018 FINAL

ACRONYMS AND ABBREVIATION

BMP best management practice CEQ Council on Environmental Quality CFR Code of Federal Regulations CY cubic yards EA Environmental Assessment EBID Elephant Butte Irrigation District FONSI Finding of No Significant Impact HUC Hydrologic Unit Code MBTA Migratory Bird Treaty Act NRCS Natural Resources Conservation Service RGCP Rio Grande Canalization Project ROD Record of Decision ROW right-of-way SOP Standard Operating Procedure SPCC Spill Prevention, Control and Countermeasure flycatcher southwestern willow flycatcher USACE U.S. Army Corps of Engineers USDA U.S. Department of Agriculture USFWS U.S. Fish and Wildlife Service USIBWC U.S. Section, International Boundary and Water Commission

RIPARIAN HABITAT COMPENSATORY MITIGATION PLAN

FOR

USACE PERMIT APPLICATION NUMBER:

SPA-2018-00084-LCO

Applicant:

United States International Boundary and Water Commission (USIBWC)

4171 N Mesa C100, El Paso TX 79902

Preparer:

Elizabeth Verdecchia, USIBWC Natural Resources Specialist, 915-832-4701 elizabeth.verdecchia@ibwc.gov

May 2, 2018

Riparian Habitat Compensatory Mitigation Plan – Sediment Basins at Thurman I and II Arroyos

USIBWC May 2018 FINAL i

RIPARIAN HABITAT COMPENSATORY MITIGATION PLAN

TABLE OF CONTENTS

1. PROJECT INFORMATION

1.1 INTRODUCTION TO COMPENSATORY MITIGATION

1.2 BACKGROUND INFORMATION

1.3 PROJECT SUMMARY

1.4 PROJECT LOCATION

1.5 DESCRIPTION OF ACTION

2. PROJECT IMPACTS AND MITIGATION

2.1 GOALS AND OBJECTIVES

2.2 SITE SELECTION

2.3 SITE PROTECTION

2.3.1 Protection Instrument

2.3.2 Site Ownership

2.4 BASELINE INFORMATION

2.4.1 Location

2.4.2 Existing Conditions

2.4.3 Classification

2.5 DETERMINATION OF CREDITS

2.6 MITIGATION WORK PLAN

2.6.1 Mitigation Approach Summary

2.6.2 Mitigation Site Selection

2.6.3 Mitigation Measures

2.7 MAINTENANCE PLAN

2.8 ECOLOGICAL PERFORMANCE STANDARDS

2.9 MONITORING REQUIREMENTS

2.10 LONG-TERM MANAGEMENT PLAN

2.11 ADAPTIVE MANAGEMENT PLAN

2.12 FINANCIAL ASSURANCES

3. LIST OF PREPARERS

4. DISTRIBUTION

5. REFERENCES

APPENDICES

A. DESIGN DRAWINGS

B. SPD MITIGATION RATIO SETTING CHECKLIST

USIBWC May 2018 FINAL ii

LIST OF FIGURES

FIGURE PAGE

Figure 1-1 Vicinity Map showing location of the Thurman I and II Arroyos in the Rio Grande

Canalization Project Figure 1-2 Local Vicinity Map of the Thurman I and II Arroyos Figure 1-3 Project Area of Thurman I and II Arroyos Figure 1-4. Design for Thurman I Sediment Basin (from Drawing 7 in Appendix A, USIBWC

2017b) Figure 1-5. Design for Thurman II Sediment Basin (from USIBWC 2017b) Figure 1-6. Drawing of End Wall for Sediment Basin (from USIBWC 2017b) Figure 2-1. Impacts to riparian vegetation from Thurman I Sediment Basin Figure 2-2. Impacts to riparian vegetation from Thurman II Sediment Basin Figure 2-3. Proposed Mitigation Areas for Thurman I Arroyo Figure 2-4. Proposed Mitigation Areas for Thurman II Arroyo

LIST OF TABLES

TABLE PAGE

Table 2-1 Summary of impacts and proposed mitigation Table 2-2 Summary of Local Groundwater Data Table 2-3 Federally listed species Known to Occur in the RGCP (USIBWC 2017a) Table 2-4 Summary of impacted areas Table 2-5 Proposed Mitigation Ratios Table 2-6 Proposed Mitigation Table 2-7 Proposed plantings at each mitigation area

May 2, 2018 FINAL, page 3

1. Project Information

1.1 Introduction to Compensatory Mitigation

The U.S. Army Corps of Engineers (USACE) and U.S. Environmental Protection Agency (EPA) regulations (33 CFR 320-331 and 40 CFR 230) authorize the USACE to require compensatory mitigation for unavoidable impacts to wetlands and other jurisdictional waters of the United States. Because the proposed project, Sediment Basins at Thurman I and II Arroyos, will impact waters of the U.S., the United States Section of the International Boundary and Water Commission (USIBWC) has applied for a Clean Water Act Section 404 permit from USACE. The permit and corresponding Compensatory Mitigation Plan were prepared in accordance with the Section 404 guidelines as well as 33 CFR Parts 325 and 332, and 40 CFR Part 230.

1.2 Background Information

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 with Mexico concluded 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 USIBWC to construct, operate, and maintain the RGCP in accordance with 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 on the west side and 74 miles on 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 (USIBWC 2017e). 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 (22 U.S.C 277).

In June 2009, the USIBWC signed the Record of Decision for River Management Alternatives for the RGCP (ROD) (USIBWC 2009), based on a 2004 Environmental Impact Statement. The ROD committed the USIBWC to continuing to implement its statutory requirements 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) (USIBWC 2015).

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 Maintenance Plan (USIBWC 2016). The final RMP incorporated results of the 2015 CMA Study.

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, Thurman I/II, Garcia, and 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 at 3,194 cubic yards (CY) (USACE 2007; USIBWC 2015).

Construction was deemed feasible because these were within USIBWC property, were not impacted by

May 2, 2018 FINAL, page 4 future USIBWC levee improvement projects, and preliminary review showed no anticipated impacts to endangered species. The USIBWC prepared an Environmental Assessment in 2017 to analyze environmental impacts for these pilot projects at Thurman I and II Arroyos (USIBWC 2017e). The original concept was several traps of mesh and rebar that would trap different sizes of sediment and rocks; this concept was redesigned in 2017 during the design phase to a sediment basin for several reasons, including better efficiency of predicted sediment trapping, structural design considerations, ease of maintenance, and scour potential.

1.3 Project Summary

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 basins 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.

The design calls for deepening and widening of the Thurman I and II arroyos within the USIBWC leveed floodplain, coupled with the construction of endwalls to create sediment basins that will allow the settling of sediment and rocks before entering the mainstem of the Rio Grande.

The construction of sediment basins will impact the Rio Grande and the ephemeral Thurman I and II arroyos. For each arroyo, the rip rap and end wall area would require 0.33 acres of fill of Waters of the U.S.

The design process included avoidance and minimization of impacts as much as possible, per 33 CFR 332.4(b), by using the method that created the lowest impact to the natural environment and mitigating for all impacts.

This mitigation plan describes the ecological conditions onsite, the project design and construction along the river, and the proposed onsite riparian zone mitigation objectives. The three types of mitigation USIBWC proposes at each site 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 than currently present along the stream banks by pooling and slowing 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. Create an embayment through construction of an endwall and protect as an aquatic habitat pool.

The total habitat proposed for mitigation covers 2.62 acres, to offset a total of 0.93 acres across both sediment basins. Each type of mitigation has its own mitigation ratio, but the overall mitigation ratio of mitigation vs impacts is 2.8 to 1.

May 2, 2018 FINAL, page 5

1.4 Project Location

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

Figure 1-3 shows the Project Area.

May 2, 2018 FINAL, page 6

Figure 1-1 Vicinity Map showing location of the Thurman I and II Arroyos in the Rio Grande Canalization Project

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Figure 1-2 Local Vicinity Map of the Thurman I and II Arroyos

Figure 1-3 Project Area of Thurman I and II Arroyos

May 2, 2018 FINAL, page 8

1.5 Description of Action

The sediment basins call for deepening and widening the arroyo channels to construct basins for sediment collection (Figure 1-4 and Figure 1-5). The basins would provide sufficient time for sediment to settle out of arroyo flows and to be deposited at the bottom of the channel. The basins would be sloped towards the river so that the larger size sediments are deposited at the beginning of the basins, and progressively finer particles are deposited further downstream. The downstream termination of the basins would be accomplished by constructing a reinforced-concrete retaining wall ("basin end wall") near the confluence with the Rio Grande (

Figure 1-6). The end wall would be approximately 4.4 to 5.7 feet above the basin finish elevation to provide freeboard for the 100-year storm flows in the arroyo. The end wall would serve as an overflow weir when higher flows occur, or when significant volumes of sediment have already been collected in the basins that permit less stormwater storage. Scour protection would be provided on both the upstream and downstream sides of the end wall (USIBWC 2017b).

The existing arroyo channels would be over-excavated to provide increased flow capacity and remove accumulated sediments. The channel bottom for Thurman I Arroyo would be excavated to approximately 1 to 2.5 feet below existing grade, and for Thurman II Arroyo, to approximately 2 to 4 feet below existing grade. The cross-section of the channel would be widened to a maximum bottom width of 150 feet for each arroyo, with permanent excavation slopes inclined at 3H:1V to maintain long-term stable slopes. Maximum channel slope heights would be approximately 9.5 and 7 feet for Thurman I and II Arroyos, respectively.

Excavated channel lengths of Thurman I and II Arroyos would be 375 and 400 feet, respectively. Estimated volumes for construction of the sediment basin at Thurman I is 10,814 cubic yards (CY) and at Thurman II is 11,744 CY (USIBWC 2017b).

May 2, 2018 FINAL, page 9

Channel slopes and bottom would be protected from erosion from both conveyance flows and surface water sheet flow related to precipitation events. Alternative C calls for 30-inch thick riprap as the most feasible erosion protection alternative for the endwall, and a 12-inch thick gabion mattress at the upstream end of the basins.

Due to the potential for channel scour/undermining and the desire to minimize excavation depths due to shallow groundwater elevations, shallow foundations were not preferred for this project. Alternative C calls for drilled pier foundations. If proposed construction occurs during the non-irrigation season, dewatering controls may be needed along approximately the downstream 1/3 of the channel alignment (USIBWC 2017b).

Based on mean annual sediment yields of 1.12 acre-feet for Thurman I Arroyo and 1.98 acre-feet for Thurman II Arroyo, and only allowing the basins to fill to 75% capacity before cleaning, the maintenance interval for the Thurman I Arroyo basin is estimated to be 3.5 years, and 2.0 years for the Thurman II Arroyo basin (USIBWC 2017b).

The USIBWC will also be excavating islands at the mouth of the arroyos, but that work will be conducted as excavation-only under a separate and independent project.

Figure 1-4. Design for Thurman I Sediment Basin (from Drawing 7 in Appendix A, USIBWC 2017b)

May 2, 2018 FINAL, page 10

Figure 1-5. Design for Thurman II Sediment Basin (from USIBWC 2017b)

Figure 1-6. Drawing of End Wall for Sediment Basin (from USIBWC 2017b)

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2. Project Impacts and Mitigation

2.1 Goals and Objectives

The overarching goal of the proposed mitigation plan is to recreate riparian habitat and functions onsite.

This will be accomplished by recreating and improving the riparian zone present along the river channel.

USIBWC has investigated several mitigation options and settled on permittee-responsible mitigation through onsite and offsite in-kind mitigation.

The mitigation plan was developed based on the practicability of implementation and compatibility with the proposed project design.

The goals of the mitigation plan are to:

Avoid and minimize impacts to waters of the U.S. and riparian areas caused by the levee construction and rehabilitation, Provide for the unavoidable impacts to a total of 0.93 acres of riparian vegetation (0.37 acres for Thurman I and 0.38 acres for Thurman II) through replacement of the chemical, physical, and biological functions of the waters of the U.S. and riparian areas displaced by the project, and

Provide for mitigation of unavoidable riparian area impacts caused by the project at an overall ratio of greater than 2.8:1 including their functions and values.

The objectives of the mitigation plan are to:

Establish 2.62 acres of total onsite aquatic and riparian habitat, Reestablish ecological functions on the river corridor such as wildlife habitat, water quality improvement, and nutrient cycling, and

Develop restoration that achieves sustainability and limits the amount of maintenance required by establishing natural processes.

This mitigation plan describes the ecological conditions onsite, the project design and construction along the river, and the proposed onsite riparian zone mitigation objectives. The three types of mitigation USIBWC proposes at each site 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 than currently present along the stream banks by pooling and slowing 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. Create an embayment through construction of an endwall and protect as an aquatic habitat pool.

Table 2-1 summarizes the impacts and proposed mitigation for each sediment basin. Each type of mitigation has its own mitigation ratio, but the overall mitigation ratio of mitigation vs impacts is 2.8 to 1.

Table 2-1 Summary of impacts and proposed mitigation Arroyo Impacts (acres) Mitigation (acres)

May 2, 2018 FINAL, page 12

Riparian vegetation at arroyo mouth

Fill (rip rap, endwall)

Total impact area

Sediment Basin Banks Plantings

River Banks Plantings

Embayment Area

Total mitigation area

Thurman I 0.08 0.39 0.47 0.27 1.07 0.14 1.48 Thurman II 0.10 0.36 0.48 0.18 0.73 0.23 1.14

SubTotals 0.45 1.8 0.37 2.62

The restoration project will replace and exceed existing functions displaced by the sediment basins. The riparian habitat will be of a better quality through desirable species recruitment coupled with nuisance and non-native invasive species control measures including spraying, cutting, and removal. Additionally, the project will create a new type of habitat in an embayment area.

2.2 Site Selection

USIBWC has selected onsite mitigation to recreate the riparian zone. This will provide a direct and reliable means to compensate for riparian habitat impacts caused by the project. Placing the mitigation along the river edge establishes connectivity with adjacent river habitats and the overall ecosystem. At low stage levels, the Rio Grande meanders within a larger channel that also conveys scheduled releases of water for irrigation and larger flood events. The design of in-kind mitigation provides the best means of directly compensating for the project impacts while also providing additional threatened and endangered species habitat.

The proposed mitigation is on land controlled and managed by USIBWC and is protected from misuse and vandalism. The current riparian zone has established vegetation through natural recruitment and preclusion of maintenance equipment, and indicates its suitability for similar vegetation in the proposed condition, based on groundwater and surface water flow regimes. It is also an indication of the likelihood of mitigation success by using similar elevations and grades to recreate functional riparian zones.

Mitigation opportunities were evaluated for this project in the context of an earlier study completed for the USACE, which was approved as part of USIBWC’s 2009 Record of Decision on River Management Alternatives for the Rio Grande Canalization Project (USIBWC 2009). The mitigation sites will enhance the much larger southwestern willow flycatcher habitat and breeding zones existing upstream and downstream of the project area and additional areas being developed for the 2009 ROD.

2.3 Site Protection

2.3.1 Protection Instrument

USIBWC controls the Rio Grande floodplain and their right-of-way defines the limits of control for management and maintenance of the river. A specific easement over the riparian habitat areas is not proposed; rather the proposed long-term management plan will meet the needs of the USIBWC’s commitment to protect the reestablished riparian zone. USIBWC will update its River Management Plan (RMP) to incorporate mitigation areas for long-term protection. USIBWC’s Biological Opinion requires USIBWC to update the RMP, so USIBWC will be going through the update process in summer 2018.

USIBWC anticipates that the RMP will be updated prior to construction.

May 2, 2018 FINAL, page 13

2.3.2 Site Ownership

USIBWC has a right-of-way over the Rio Grande including the riverbed, floodplain, and levees. All proposed activities are located within USIBWC right-of-way.

2.4 Baseline Information

2.4.1 Location

The project area is within the Rio Grande drainage region (Region 13) in Hydrologic Unit 12 Code (HUC-

12) 130301020403 (Hammett Dam-Rio Grande). The drainage area of HUC-12 130301020403 is 31,620 acres (USGS 2018).

The coordinates of the confluence of the Thurman I arroyo with the Rio Grande are latitude 32.682814° and longitude -107.176771°, and the Thurman II arroyo confluence is at latitude 32.684542° and longitude -107.182758°. The proposed onsite mitigation area is at the mouth of each of the arroyos as well as the adjacent banks of the Rio Grande.

2.4.2 Existing Conditions

The USIBWC evaluated existing impacts in the Final Environmental Assessment: Channel Maintenance Alternatives at Thurman I and II Arroyos in Hatch, NM, Rio Grande Canalization Project, December 2017 (USIBWC 2017e).

Soils

The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) mapped soils in Dona Ana County, New Mexico (NRCS 2018a). The NRCS identified the following soil mapping units with the Doña Ana County area (Area NM690):

in the Thurman I project area - Brazity loamy fine sand (Br);

in the Thurman II project area – Belen loam (Be) (in the upstream portion of Thurman II within USIBWC ROW) and Brazito very fine sandy loam, thick surface (Bs) (near the confluence with the Rio Grande).

None of the soils mapped by the NRCS in the Thurman I or II project areas are designated as hydric (NRCS 2018b).

USIBWC conducted soil testing in 2010 and again in 2013 at nearby locations, although soil salinity has not been collected in the project area. Both studies show that salinity levels are highly variable throughout the project vicinity, but both tend to show that surface samples generally have higher soil salinity than subsurface samples. In the 2013 study, samples collected throughout the project were mostly non-saline to slightly saline, with a few samples in the moderately saline range. Samples from Crown Canyon A and B sites about 4 miles north of Thurman II had conductivity ranging from 0 to 2.845 mS/cm, and the Rincon Siphon site about 3 miles downstream of Thurman I had conductivity ranging from 0 to 3.2 mS/cm

May 2, 2018 FINAL, page 14

(USIBWC 2014). For comparison, USDA states that native cottonwoods and willows may not tolerate salinity levels in the 3 to 4 mS/cm range (NRCS undated). The 2010 study samples showed similar ranges for the upstream and downstream sites, although soil salinity peaked at 5.24 mS/cm at the downstream Rincon Siphon site (USIBWC 2010). In general, soil salinity should be conducive to planting riparian vegetation, with pockets of areas where soil saline is higher that may prevent thriving of riparian vegetation.

Surface Water

The Thurman I and II sediment basin projects are entirely within the Rio Grande watershed, in the floodplain within USIBWC RGCP levees. The Rio Grande flows from north to south through the project.

The Garfield Drain discharges to the Rio Grande on its eastern bank immediately upstream of Thurman II arroyo.

The available water within the river throughout the year is highly variable. In recent years, the project area has been completely dry during non-irrigation season in the winter months. Irrigation season during full allotment years has typically been from March to October; however, in low water years, irrigation season has begun later and ended earlier, and the river may only flow for 2 or 3 months during June through August.

The 2013 irrigation season was the shortest on record and only lasted 6 weeks from June through mid-July.

Irrigation season is based on levels within Elephant Butte and Caballo Reservoirs as well as local rainfall and upstream snow packs. Irrigation season is established by a binational delegation in coordination with the Rio Grande Compact, the Bureau of Reclamation, local irrigation districts, the USIBWC, and Mexican counterparts. Photo 1 shows typical conditions in the non-irrigation season, with some pools of water in an otherwise dry Rio Grande. Because of accumulated sediment in the Rio Grande at the mouth of these arroyos, surface flows from the Rio Grande back up into the arroyos during irrigation season for about a hundred feet (Photo 5).

Photo 1. Panoramic view of the Thurman I delta in the Rio Grande, Feb 2016

Groundwater

The Rio Grande aquifer system corresponds to the eastern part of the Southwest alluvial basins aquifer system, which is a large system of aquifers in alluvial basins in the southwestern United States and Mexico.

The alluvial aquifers are found in six major basins: the Mesilla, the Hueco, the Salt, the Eagle, the Red Light, and the Presidio. The basin areas are filled with thick sequences of clastic sediments that have eroded from the adjacent highlands. The basin deposits are late Tertiary and Quaternary in age and consist mostly of clay, silt, sand, and gravel. The Thurman I and II project areas are located in the Mesilla Basin (USGS 1995).

The Rio Grande alluvium is part of the Mesilla Basin alluvial aquifer. It overlies the Mesilla Basin and cannot be easily distinguished from it; the shallow groundwater has been shown to be hydrologically connected to the Rio Grande (USGS 1995; USBR 2016). The total thickness of the unconsolidated deposits

May 2, 2018 FINAL, page 15 in the Mesilla Basin is estimated to be at least 2,000 feet, and the thickness of the Rio Grande alluvium is 150 feet or less. The chemical quality of the water in the shallower part of the aquifer is influenced by the quality of the water in the Rio Grande. The depth of fresh water extends to as much as 1,400 feet below land surface. The water in the shallower part of the aquifer is generally more mineralized than that in the deeper part. The aquifer receives recharge by infiltration of runoff around the basin margins, and from seepage from the Rio Grande, ephemeral streams, canals, and excess irrigation water (USGS 1995).

In 2013 and 2014, USIBWC installed a network of 55 shallow groundwater monitoring wells on 18 USIBWC active or planned restoration sites and 2 additional floodplain locations. Wells span the 105-mile RGCP. Six wells are located 4 miles north of the Thurman I and II project areas in Hatch, NM, and another 6 wells are located 3 miles south in Rincon. NM. Data from the north wells (CCB-MW-1, CCB-MW-2, CCB-MW-1, CCA-MW-1, CCA-MW-2, and CCA-MW-3) indicate that groundwater levels vary between 4 and 14.6 feet below the ground surface throughout the irrigation and non-irrigation season, although most wells seem to hover around 10 feet below the surface in the non-irrigation season. Data from the south wells (RS-MW-7, RS-MS-6, RS-MW-5, RS-MW-4, RS-MW-2, RS-MW-1) indicate that groundwater levels vary from 1.24 to 14.19 feet below the ground surface throughout the irrigation and non-irrigation season, although most wells seem to hover around 9 feet below the surface in the non-irrigation season.

Local groundwater level data were evaluated by URS in the design of the sediment basins and summarized in Table 2-2 (USIBWC 2017b, Table 6-3). Groundwater levels vary greatly and range from 2 to 16 feet below the surface.

Table 2‐2 Summary of Local Groundwater Data

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May 2, 2018 FINAL, page 17

In February 2017, USIBWC contractors, while working on one of the Hatch restoration sites (Crow Canyon C) excavated trenches to plant riparian trees, and during their excavation, they encountered highly variable groundwater levels from 7 to 14 feet below the surface. In late May 2014 when the river was its driest prior to 2014 irrigation releases, wells below Mesilla Dam (from Below Mesilla Dam to Sunland Park, New Mexico) consistently showed that groundwater levels ranged from 6.5 feet to almost 19 feet below the surface, with median value being 10.6 feet and mean value of 11.1 feet (USIBWC unpublished data). In late June 2014, after irrigation season had begun and irrigation flows had been in the river for several weeks, data showed that wells below Mesilla Dam still had highly variable groundwater levels from 2 to 8 feet below the surface. In 2015 to 2017, irrigation flows improved and so did groundwater levels. The USIBWC groundwater monitoring well data are revealing declining groundwater levels with declining surface flows in the Rio Grande. Limited groundwater is available for riparian vegetation during critical months of winter and early spring, and quickly decline in the fall months.

Local groundwater pumping for supplemental irrigation is widely accepted as the primer driver for declining groundwater levels and large fluctuations in groundwater and impacts to available surface water (USGS 1995, USBR 2016, USIBWC unpublished data), and groundwater pumping for irrigation is the largest component of groundwater demand in the region, particularly during dry years (USBR 2013c). In 2005, New Mexico Office of the State Engineer, who regulates groundwater in New Mexico, estimated that groundwater pumping for irrigation in the Rincon and Mesilla Valleys in New Mexico, the majority of which occurs within Elephant Butte Irrigation District (EBID) to supplement Rio Grande Project surface water supplies, is between 200,000 and 300,000 AFY in dry years (USBR 2013c). Existing groundwater pumping includes municipal pumping, irrigation pumping for lands irrigated with groundwater only, and supplemental irrigation pumping for lands that receive Project water. (USBR 2013c). Pumping of

May 2, 2018 FINAL, page 18 groundwater lowers the water table and increases the loss of river and canal flows to the aquifer, as river flows recharge the aquifers to replenish the water that has been removed (USBR 2013c).

Vegetation

The RGCP is located in the northern Trans-Pecos region of the Chihuahuan Desert. This region includes all sections of the Chihuahuan Desert in the U.S. and the northernmost sections of the desert of Mexico (McMahan 1984). Climatic conditions throughout the study area are classified as semi-arid continental, characterized by fairly hot summers, mild winters, and short temperate spring and fall seasons. Precipitation averages 7.7 inches per year. The Trans- Pecos region of the Chihuahuan Desert is historically a mosaic of grasslands and desert shrublands (McMahan 1984).

Grasses and other vegetation within the floodplain within the levees in this area are mowed regularly to ensure suitable design flood features and to prevent degradation of the structural integrity of the levees (USIBWC 2016). Photo 2 shows the mowed floodplain at Thurman I, and Figure 9 shows the floodplain at Thurman II.

Photo 2 Mowed floodplain on north side of Thurman I (west bank), looking upstream

Some riparian vegetation exists at the confluence of the arroyos and the Rio Grande. Mixed native (willows, cottonwood, seep willow) and nonnative vegetation (saltcedar) exists along the mouth of the arroyos, as shown in Photos 3 and 4. Additionally, vegetation grows on accumulated sediment (sandbar) at the confluence of the Rio Grande (Photo 5). Along the banks of the Rio Grande adjacent to the arroyos, riparian vegetation consists mainly of exotic saltcedar mixed with some nave coyote willows (Photo 6, 7 and 8).

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Photo 3. Vegetation at the mouth of Thurman I near confluence with Rio Grande during non-irrigation season February 2016.

Photo 4. Vegetation at the mouth of Thurman I near confluence with Rio Grande during irrigation season, July 2016.

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Photo 5. Foreground -Vegetation on sediment bar at the mouth of Thurman I near confluence with RG. Background -vegetation on the east bank of Thurman I. Feb 2016

Photo 6. Vegetation along the banks of the Rio Grande, looking at confluence of Thurman I from the Thurman I delta inside RG. February 2016.

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Photo 7. Vegetation at the mouth of Thurman II, looking from the arroyo to the Rio Grande, July 2016.

Photo 8. Vegetation at the mouth of Thurman II, looking from the Rio Grande up to arroyo, Feb 2016.

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Photo 9. Thurman II arroyo looking downstream to the Rio Grande.

Wildlife Species and Habitat Use

Typical wildlife that could inhabit the project area include black-tailed jackrabbit (Lepus californicus), desert cottontail (Sylvilagus audubonii), cotton rat (Sigmodon hispidus), ground squirrels (Otospermophilus beecheyi), mourning dove (Zenaida macroura), meadowlark (Sturnella neglecta), American kestrel (Falco sparverius), red-tail hawk (Buteo jamaicensis), mule deer (Odocoileus hemionus), skunks (Mephitis mephitis), burrowing owls (Athene cunicularia), several species of waterfowl, and other non-game animals

(USIBWC 2007).

In addition, habitat could potentially be utilized by migratory birds. The Migratory Bird Treaty Act (MBTA) (16 U.S.C. 703-712, [1918, as amended 1936, 1960, 1968, 1969, 1974, 1978, 1986 and 1989]) requires that Federal agencies coordinate with the USFWS if a construction activity would result in the take of a migratory bird. The MBTA protects migratory birds, their parts, nests, and eggs thereof during their nesting season. The U.S. Fish and Wildlife Service (USFWS) has determined that the nesting season for the region including the RGCP area is March 1 through August 15, and may be extended to September 1 if birds are still nesting.

Threatened and Endangered Species

In preparation of the 2004 EIS, biological surveys were conducted along the RGCP to identify T&E species potentially occurring within the RGCP (Parsons 2001); additional biological assessments were conducted in 2004, 2011, and 2017 (USIBWC 2004; USIBWC 2011; USIBWC 2017a). Of the 14 species listed as endangered, threatened, candidate, proposed, or experimental nonessential population, four have been documented or have the potential to occur in the RGCP and are listed in Table 2-3 (USIBWC 2017a). More detailed information regarding threatened and endangered species potentially occurring in RGCP is available in the Updated Biological Assessment for Long-Term River Management of the Rio Grande Canalization Project (USIBWC 2017a Appendix B).

May 2, 2018 FINAL, page 23

The USIBWC, in coordination with the U.S. Bureau of Reclamation, has identified known nesting sites for the flycatcher and continues to conduct annual presence/absence surveys. The Thurman I and II project areas are not identified as a nesting area for the flycatcher, the yellow-billed cuckoo, or any other endangered species. There is no critical habitat designation in the project area (USIBWC 2017a).

However, there is suitable breeding or migratory habitat for the flycatcher and the cuckoo in the immediate vicinity of Hatch, NM. Flycatcher territories have been observed in 2013 and previous years about 0.25 miles upstream of Thurman II, and in 2015 about 0.5 mile downstream of Thurman I.

However, no cuckoos or flycatchers have been observed in 0.5-mile immediate vicinity since 2015, nor does the immediate project area provide suitable breeding or migratory habitat for the flycatcher or the cuckoo (USIBWC 2011; USBR 2013a; USBR 2013b; USBR 2013c; USBR 2016; USIBWC 2017a).

In 2012, the USIBWC concluded Endangered Species Act Section 7 consultation with the USFWS regarding potential impacts to the flycatcher for implementation of the USIBWC 2009 ROD (USIBWC 2009) which resulted in 2012 Biological and Conference Opinion (USFWS 2012). In 2017, USIBWC re-consulted with the USFWS on the potential impacts to T&E species as a result of channel maintenance activities documented in USIBWC’s River Management Plan for RGCP (USIBWC 2016), and USIBWC has been issued an updated Biological Opinion for the actions (USFWS 2017). The updated Biological Opinion allows the USIBWC to remove some vegetation within the channel that is suitable for the flycatcher as long as USIBWC continues to implement riparian habitat restoration and follows other requirements and recommendations (USFWS 2017).

Table 2‐3 Federally listed species Known to Occur in the RGCP (USIBWC 2017a)

Common Name (Species Name)

Status County where listing Applies

Range or Habitat Requirements Potential for Occurrence in RGCP

Potential timeframe for Occurrence

Southwestern Willow Flycatcher (Empidonax traillii extimus)

E Sierra and Doña Ana Counties, El Paso County

Associated with moist riparian areas throughout the year. Documented on some RGCP restoration sites.

Known to occur

Breeding resident during summer;

migrates to tropics

Northern Aplomado falcon (Falco femoralis septentrionalis)

E and

ENEP

Sierra and Doña Ana Counties, El Paso County

Documented at Mesilla Valley Bosque State Park in 2010.

Associated with open grassland or savannah with scattered trees or shrubs. Experimental population in

NM.

Known to occur

Nests spring to summer. Non‐ migratory

Least tern (Sterna antillarum)

E Sierra and Doña Ana Counties

Migratory species occurring in North America during the breeding season, when it is associated with water (e.g. lakes, reservoirs, rivers) Documented in the RGCP including at Mesilla

Known to occur

Possible breeding resident summer

Yellow‐billed Cuckoo (Coccyzus americanus)

T Sierra and Doña Ana Counties, El Paso County

Western subspecies nests preferentially in large patches of moist cottonwood‐willow woodland, where it prefers high canopy closure for nesting.

Documented on some proposed RGCP restoration sites

Known to occur

Breeding resident summer

E = Endangered T=Threatened ENEP=Experimental, Non‐essential Population

May 2, 2018 FINAL, page 24

2.4.3 Classification

For these sediment basins, USIBWC assumed that all impacted waters were jurisdictional and therefore no wetland classification was conducted. USIBWC conducted site visits in February and July of 2016 and determined that no wetlands are present in the area. Riparian areas were delineated based on high resolution aerial imagery from Digital Globe from November 20, 2017, and cross referenced with aerial imagery from winter 2011 and summer 2015 as well as field visits and photographs. Impacts to Waters of the U.S. are listed in Table 2-4 and shown in Figures 2-1 and 2-2. Impacts were calculated based on the total fill from rip rap and end wall areas, as well as impacts to riparian vegetation. USIBWC believes the impact calculations are conservative because it includes non-native vegetation such as saltcedar. The sediment basins will be excavated with scrapers and therefore will be excavation-only. Total impacts are slightly under 1/2 acre for each arroyo.

The banks of the arroyos are unconsolidated material, as seen in Photo 9. USIBWC determined that the ordinary high water mark (OHWM) was the limit of the current arroyo banks, and estimated from the high resolution imagery, as outlined in Figures 2-1 and 2-2. Impacts below the OHWM are also listed in Table 2-4. Using this methodology, USIBWC estimates that the projects will impact 0.28 acres of riparian vegetation and fill below the OHWM at Thurman I and 0.36 acres at Thurman II.

Table 2-4 Summary of impacted areas Arroyo Impacts (acres)

Riparian vegetation at arroyo mouth

Fill (rip rap, endwall)

Total impact area

Impacts below the

OHWM

Thurman I 0.08 0.39 0.47 0.28 Thurman II 0.10 0.36 0.46 0.36

May 2, 2018 FINAL, page 25

Figure 2-1. Impacts to riparian vegetation and fill from Thurman I Sediment Basin

Figure 2-2. Impacts to riparian vegetation and fill from Thurman II Sediment Basin

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2.5 Determination of Credits

Per Code of Federal Regulations (CFR), Part 332.3 (a)(1) the fundamental objective of compensatory mitigation is to offset environmental losses resulting from unavoidable impacts to waters of the U.S.

Furthermore, 33 CFR, part 332.3 (f)(1), states that the amount of required compensatory mitigation must be, to the extent practicable, sufficient to replace lost aquatic resource functions, and should be at least one-to-one acreage of linear foot compensation. The district engineer must determine the compensatory mitigation to be required in a Department of the Army permit, based on what is practicable and capable of compensating for the aquatic resource functions that will be lost as a result of the permitted activity.

In order to determine required mitigation for the Thurman sediment basins, USIBWC used USACE South Pacific Division 12501-SPD Regulatory Program Standard Operating Procedure for Determination of Mitigation Ratios (USACE 2017).

Appendix B shows the USACE South Pacific Division (SPD) Mitigation Ratio Setting Checklist for both sediment basins. Mitigation ratios for the different types of proposed mitigation are summarized in Table 2-5.

Table 2-5 Proposed Mitigation Ratios Name Sediment Basin Banks Plantings River Banks Plantings Embayment Area Ratio 4.56:1 4.75:1 0.75:1

Notes

Riparian Establishment Type conversion ephemeral stream to riparian Up to 9-month construction delay Permitee responsible mitigation Willow trees Rip rap Modified hydrology Mitigation site did not formerly support the species

Riparian Enhancement Up tp 9-month construction delay Permitee responsible mitigation Willow trees Modified hydrology

Aquatic Habitat/Embayment

Establishment 9-month construction delay Permitee responsible mitigation Modified hydrology

2.6 Mitigation Work Plan

The Council on Environmental Quality (CEQ) has provided guidance on the use of mitigation and supports the use of mitigation to lead to a Finding of No Significant Impact (FONSI). Per 40 Code of Federal Regulations (CFR) 1508.20, as described in the CEQ Regulations, agencies can use mitigation to reduce environmental impacts in several ways. 33 CFR Part 332.3(e)(1) provides a description of the type of mitigation required specific to a 404 permit, stating “required compensatory mitigation shall be of a similar type to the affected aquatic resource.” Mitigation includes:

• Avoiding an impact by not taking a certain action or parts of an action;

• Minimizing an impact by limiting the degree or magnitude of the action and its implementation;

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• Rectifying an impact by repairing, rehabilitating, or restoring the affected environment;

• Reducing or eliminating an impact over time through preservation and maintenance operations during the life of the action; and

• Compensating for an impact by replacing or providing substitute resources or environments.

2.6.1 Mitigation Approach Summary

The USIBWC proposes to mitigate for the loss of riparian habitat in the project area and for the change in hydrology of the ephemeral stream by the following three types of mitigation:

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 than currently present along the stream banks by pooling and slowing 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. Establish an embayment on the river side of the constructed end wall and protect as an aquatic habitat pool.

As listed in Table 2-1 the total loss of riparian habitat and fill of waters of the U.S. from both sediment basins amounts to 0.93 acres. To ensure adequate mitigation, USIBWC has included areas above the OHWM, as shown in Table 2-4. The onsite mitigation for this project is 2.62 acres, as shown in Table 2- 6, being proposed at an overall ratio of 2.8:1. Mitigation areas are shown in Figures 3 and 4.

Table 2-6 Proposed Mitigation

Arroyo

Mitigation

Sediment Basin Banks Plantings

River Banks Plantings Embayment

Area

Total mitigation area Linear Feet

Acres Total Acres

Linear Feet

Acres Total Acres

Total Acres Total Acres

Thurman I 189 N 242 S

0.11 N

0.16 S

0.27 325 N 368 S

0.42 N

0.65 S

1.07 0.14 1.48

Thurman II 218 N 198 S

0.1 N

0.08 S

0.18 327 N 362 S

0.32 N

0.41 S

0.73 0.23 1.14

Totals 0.44 1.12 0.30 2.62

Mitigation operations will be performed in accordance with guidance as published in the USDA New Mexico Natural Resources Conservation Service and the New Mexico Association of Conservation Districts guide entitled, “A Guide for Planning Riparian Treatments in New Mexico” (NRCS 2007). Native plantings will consist of coyote willows, Goodding’s willows (also called black willows), and cottonwood trees. Longstem shrubs will consist of native plants such as three leaf sumac, New Mexico olive, desert willow, false indigo, and baccharus/seep willow. Mitigation contractors may use other native species if they are cleared with USIBWC first. USIBWC will consult with USACE for proposed changes to the plant species.

One option for a source of willows is to harvest the vegetation from the nearby islands and transplant via trenches along the banks. Willows and about one to one and a half feet of topsoil with roots can be extracted with a front-end loader from nearby islands (that will be removed by USIBWC under separate and

May 2, 2018 FINAL, page 28 independents projects for USIBWC’s routine channel maintenance) and carried to the mitigation site where they can be transplanted into trenches to ground level. This option is currently being tested by USIBWC in other locations and if successful may be implemented as part of this mitigation. The willow root ball method is more successful than cuttings and is preferred to coyote willow cuttings. Pole cuttings are preferred for cottonwoods and Gooddings willows.

USIBWC Contractors will apply certain restoration techniques to increase the percent cover of the pole plantings. Such techniques include planting several poles per hole to increase survival rate and density, as well as lopping off the top of the poles at the ground level at random and scattered holes to promote leafout from the base of the pole in order to increase density and percent cover.

At all mitigation sites, USIBWC Contractors will also be required to water the planted poles with water trucks at least twice in the first season after planting but prior to irrigation releases in order to promote root growth and plant vigor. In addition, USIBWC will initiate a nonnative and invasive species control plan including herbicide spraying, cutting, and pulling as necessary on a biannual basis before and after the rainy season. Particular species among others to be controlled include salt cedar and common reed.

Construction is currently scheduled to occur in the dry season (non-irrigation season) from October 2018 to February 2019. Mitigation will be conducted following the construction. The mitigation will begin as soon as the new banks have been established, with a target start timeframe of February 2019; however, if timing does not permit due to construction, then planting may begin in the fall of 2019 and thus the 9-month delay included in the mitigation ratio setting checklist. After construction is complete, the disturbed areas in the floodplain will be reseeded with native grasses.

This mitigation plan accommodates environmental conditions in the river including low and highly variable rainfall, controlled and intermittent river flows, and larger vegetation cover that is usually controlled by land management practices of the USIBWC, including mowing and cutting. This onsite mitigation plan, using both active plantings and recruitment of vegetation, will establish vegetative cover similar to that present in the existing condition. In addition, this plan will provide as much as practicable onsite mitigation through the enhancement of riparian habitat zone on the river. This mitigation plan also proposes to create an embayment area on the riverside of the end wall that can act as a refuge for aquatic habitat species, provide slight energy dissipation, and provide short-term water storage.

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Figure 2-3. Proposed Mitigation Areas for Thurman I Arroyo

Figure 2-4. Proposed Mitigation Areas for Thurman II Arroyo

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2.6.2 Mitigation Site Selection

Establishment of Riparian Area on Sediment Basin Banks

USIBWC proposes to establish an onsite riparian area along the eastern and western slopes of the sediment basin. After construction of the sediment basin, the banks will be stabilized and with native riparian species, consisting of a majority of coyote willow with some cottonwood and Gooddings willows as well as native longstem riparian shrubs including seep willow (baccharus) and grasses.

USIBWC has determined that the sediment banks mitigation area will have a functional gain from the impact site because the impact site has no vegetation within the floodplain, and the mitigated site will create moist conditions for riparian vegetation to grow, where it currently does not. Moist conditions are from the dissipated energy which will pool water and because the area will be excavated lower to groundwater.

Embayment and Rio Grande Banks Plantings Mitigation

USIBWC proposes to establish an onsite riparian area along the eastern and western slopes of the sediment basin. After construction of the sediment basin, the banks will be stabilized and with native riparian species, consisting of a majority of coyote willow with some cottonwood and Gooddings willows as well as native shrubs including seep willow (baccharus). Additionally, USIBWC has designated the bank area for up to 30 feet as a No-Mow Zone, thereby allowing the river’s edge and embankment area to recruit mesic and wetland vegetation including three square, coyote willow, mule fat, acacia, and other species. This vegetation will naturally recruit and establish onto the near-shore embankment to fill in tree plantings that are installed following construction. Thurman II flows adjacent to the Garfield Drain, managed by the EBID. Mitigation will not impact the drain confluence with the Rio Grande.

Embayment Area

The riverside of the endwall will create an embayment area that will act as small backwater area for aquatic habitat.