Final_Vegetation_Management_Plan.pdf

Final Vegetation Management Plan

Clearing Areas along the Arroyo Colorado Floodway in the

Lower Rio Grande Flood Control Project Area Cameron County, Texas

Prepared for:

International Boundary and Water Commission United States Section, Headquarters

4171 North Mesa, Suite C100 El Paso, Texas 79902-1441

Contract No. IBM15D0005 Order No. IBM15T0013

Prepared by:

Gulf South Research Corporation

8081 Innovation Park Drive Baton Rouge, Louisiana 70820

Final November 2015 Revised 12 January 2016 IBWC

Arroyo Colorado Floodway i Final November 2015 Vegetation Management Plan Revised 12 January 2016 IBWC

TABLE OF CONTENTS

1.0 INTRODUCTION.......................................................................................................... 1-1

1.1 Responsible Parties .............................................................................................. 1-1

1.2 Project Area Location .......................................................................................... 1-4

1.3 Existing Conditions .............................................................................................. 1-4

1.4 Objective and Purpose ......................................................................................... 1-6

1.5 Need for a Vegetation Management Plan ............................................................ 1-7

2.0 VEGETATION REMOVAL EFFORTS ..................................................................... 2-1

2.1 Conservation Measures ........................................................................................ 2-2

2.2 Threatened and Endangered Species ................................................................... 2-3

3.0 POST-CLEARING REVEGETATION....................................................................... 3-1

3.1 Safety and Protection ........................................................................................... 3-1

3.2 Erosion Prevention Measures .............................................................................. 3-1

3.3 BMPs.................................................................................................................... 3-4

3.4 Timing .................................................................................................................. 3-4

3.5 Site Preparation .................................................................................................... 3-4

3.6 Seeding Methods and Equipment ........................................................................ 3-5

3.6.1 Broadcast Seed Application (Recommended) .......................................... 3-5

3.6.2 Drill-Seed Application ............................................................................. 3-5

3.6.3 Hydro-Seed Application ........................................................................... 3-5

3.7 Supplemental Irrigation ....................................................................................... 3-6

3.8 Materials Specifications ....................................................................................... 3-6

3.9 Seed Mixes ........................................................................................................... 3-7

3.10 Water .................................................................................................................... 3-8

3.11 Straw .................................................................................................................... 3-8

3.12 Tackifier ............................................................................................................... 3-8

3.13 Wood Fiber .......................................................................................................... 3-9

3.14 Equipment and Tools ........................................................................................... 3-9

3.15 Adaptive Management Techniques...................................................................... 3-9

4.0 LONG-TERM VEGETATION MAINTENANCE ..................................................... 4-1

4.1 Containerized Plantings ....................................................................................... 4-1

4.2 Mowing ................................................................................................................ 4-3

4.3 Mechanical Removal of Woody Species Resprouts ............................................ 4-3

4.4 Invasive Woody Plant Species Control ................................................................ 4-3

4.5 Herbivores ............................................................................................................ 4-5

4.6 Floods ................................................................................................................... 4-5

4.7 Compliance with the MBTA ................................................................................ 4-5

5.0 MONITORING PLAN .................................................................................................. 5-1

5.1 Monitoring ........................................................................................................... 5-1

5.2 Final Success Criteria .......................................................................................... 5-2

5.3 Monitoring Reports .............................................................................................. 5-2

Arroyo Colorado Floodway ii Final November 2015

5.4 Completion of Monitoring Requirements ............................................................ 5-2

6.0 REFERENCES ............................................................................................................... 6-1

LIST OF FIGURES

Figure 1-1. Vicinity Map ........................................................................................................ 1-2 Figure 1-2. Woody Vegetation Clearing and Revegetation Areas along the Arroyo Colorado

Floodway.............................................................................................................. 1-3 Figure 3-1. Herbaceous and Woody Shrub Species Revegetation along the Arroyo Colorado

Floodway Channel ............................................................................................... 3-2 Figure 4-1. Conceptual Diagram of Revegetation with Herbaceous and Woody Shrub Species along the Arroyo Colorado Floodway Channel ................................................... 4-2

LIST OF TABLES

Table 3-1. Curlex I Fibrenet Erosion Control Blanket Specifications .................................. 3-3 Table 3-2. Hydro-Seed Mix Components ............................................................................. 3-6 Table 3-3. Native Herbaceous Plants to Include in Seed Mix ............................................... 3-7 Table 4-1. Recommended Containerized Native Shrub Plantings ........................................ 4-1 Table 5-1. Visually Estimated Cover Class System Used to Estimate Absolute Percent Cover of Herbaceous Plants (modified from Daubenmire 1959) ................................... 5-2 Table 5-2. Final Success Criteria .......................................................................................... 5-2

LIST OF PHOTOGRAPHS

Photograph 1-1. Typical woody vegetation within the Arroyo Colorado Floodway channel riparian areas .................................................................................................. 1-5

Photograph 1-2. Typical herbaceous understory species within the Arroyo Colorado Floodway channel riparian areas ................................................................... 1-5

Photograph 1-3. Common reed and carrizo cane along the Arroyo Colorado Floodway channel banks ................................................................................................. 1-6

Photograph 3-1. Curlex I Fibrenet Erosion Control Blanket (courtesy of American Excelsior Company) ....................................................................................................... 3-3

Arroyo Colorado Floodway 1-1 Final November 2015

1.0 INTRODUCTION

The International Boundary and Water Commission, United States Section (USIBWC) contracted Gulf South Research Corporation (GSRC) to prepare a Vegetation Management Plan for clearing areas along the Arroyo Colorado Floodway in the Lower Rio Grande Flood Control Project (LRGFCP) area in Cameron County, Texas (Figure 1-1). The USIBWC, Operations and Maintenance Division, has reinstated a woody vegetation removal project along the Arroyo Colorado Floodway in order to reestablish and maintain the design flood conveyance within the channel.

The Arroyo Colorado Floodway makes up part of the LRGFCP. The LRGFCP is one of three flood control systems operated and maintained by the USIBWC along the Rio Grande. The USIBWC is authorized to construct, operate, and maintain any project or works constructed by the United States on the LRGFCP, as authorized by the Act of the 74th Congress, Sec. I Ch. 561 (House Resolution [HR] 6453), approved August 19, 1935 (49 Stat 660), and codified at 22 United States Code (U.S.C.) Sections 277, 277a, 277b, and 277c, and Acts amendatory thereof and supplementary thereto.

The LRGFCP is composed of 270 miles of levee and floodways, as well as the Arroyo Colorado Floodway, which extends from Anzalduas Dam, located approximately 13 miles downstream from Peñitas, Texas, to beyond Brownsville, Texas. The Arroyo Colorado Floodway is one of three floodways that make up the interior floodway of the LRGFCP. The interior floodway consists of the Main Floodway, which splits into the North Floodway and the Arroyo Colorado Floodway at the City of Mercedes, Texas. The Arroyo Colorado Floodway has a design capacity of 21,000 cubic feet per second (cfs) and conveys flood flows diverted from the Rio Grande east to the Laguna Madre.

The USIBWC maintains and controls woody vegetation within the Arroyo Colorado Floodway channel and along its banks to reduce erosion potential, remove potential obstructions that could reduce design flood conveyance capacity, help stabilize stream banks, control weed and brush, including invasive species, and provide wildlife habitat at suitable locations. Vegetation is managed by mowing, by mechanical or chemical treatment, through provisions in leases, or through cooperative agreements for recreation areas.

The USIBWC will continue to mechanically remove woody vegetation and to maintain and mow grass and brush within an approximately 45-acre area along the Arroyo Colorado Floodway between Business 77 and Farm to Market (FM) 509 in Harlingen, Cameron County, Texas (Figure 1-2).

1.1 Responsible Parties

The USIBWC is responsible for all vegetation maintenance and for funding the revegetation program described in this plan. In addition, the USIBWC will be responsible for all work conducted or contracted for this program, including vegetation removal and revegetation along the Arroyo Colorado Floodway between Business 77 and FM 509.

Arroyo Colorado Floodway 1-2 Final November 2015

Figure 1-1. Vicinity Map

Arroyo Colorado Floodway 1-3 Final November 2015

Figure 1-2. Woody Vegetation Clearing and Revegetation Areas along the Arroyo Colorado Floodway

Arroyo Colorado Floodway 1-4 Final November 2015

1.2 Project Area Location

The USIBWC’s woody vegetation removal efforts are focused along an approximately 45-acre portion of the Arroyo Colorado Floodway channel between Business 77 and FM 509 in Harlingen, Cameron County, Texas (see Figure 1-2). This particular reach of the Arroyo Colorado Floodway experienced unexpected flood levels during Hurricane Alex in 2010. The riparian area and floodplain within this reach contain woody vegetation, including small trees and shrubs, but in general do not contain thick closed-canopy thornscrub habitat.

1.3 Existing Conditions

Surveys for the presence or absence of threatened and endangered plant species within areas along the Arroyo Colorado Floodway were completed on September 14-17, 2015, with a follow-up survey on November 4, 2015. The surveys focused primarily on threatened and endangered plant species that could occur within the Arroyo Colorado Floodway, with particular focus on the Federally listed south Texas ambrosia (Ambrosia cheiranthifolia), Texas ayenia (Ayenia limitaris), and star cactus (Astrophytum asterias). The area was also surveyed for presence of other rare plants, areas of potential habitat for migratory birds, and travel habitat for the endangered Gulf Coast jaguarundi (Herpailurus yagouaroundi cacomitli) and ocelot (Leopardus pardalis).

Common trees observed during surveys included Texas ebony (Chloroleucon ebano), huisache (Acacia farnesiana), retama (Parkinsonia aculeata), hackberry (Celtis laevigata), saltcedar (Tamarix sp.), Brazilian pepper (Schinus terebinthifolius), lead tree (Leucaena leucocephala), honey mesquite (Prosopis glandulosa), and ash (Fraxinus sp.) (Photograph 1-1). Dominant shrub species included baccharis (Baccharis salicifolia), Texas sabal palms (Sabal mexicana), shrubby blue sage (Salvia ballotiflora), and sea oxeye daisy (Borrichia frutescens) (Photograph 1-2).

Understory species, such as guinea grass (Urochloa maxima), Kleberg bluestem (Dichanthium annulatum), Rio Grande dewberry (Rubus riograndis), little head gum weed (Grindelia microcephala), hairypod cowpea (Vigna luteola), many-spiked flat sedge (Cyperus polystachyos), buffelgrass (Cenchrus ciliaris), and sprawling lippia (Lippia alba), were also commonly observed during surveys (Photograph 1-2). In addition, common reed (Phragmites australis), carrizo cane (Arundo donax) (Photograph 1-3) and castor bean (Ricinus communis) were abundant throughout the survey area.

No potential habitat for south Texas ambrosia, Texas ayenia, or star cactus was observed within the survey area, and none of these protected species were encountered during survey efforts.

Patches of woody vegetation were present that could provide for suitable habitat for migratory birds and potential riparian travel corridor habitat for small mammals, including the endangered Gulf Coast jaguarundi and ocelot.

Arroyo Colorado Floodway 1-5 Final November 2015

Photograph 1-1. Typical woody vegetation within the Arroyo Colorado Floodway channel riparian areas

Photograph 1-2. Typical herbaceous understory species within the Arroyo Colorado Floodway channel riparian areas

Arroyo Colorado Floodway 1-6 Final November 2015

Photograph 1-3. Common reed and carrizo cane along the Arroyo Colorado

Floodway channel banks

1.4 Objective and Purpose

The primary objective of this effort is to develop a Vegetation Management Plan for the Arroyo Colorado Floodway that supports the design flood conveyance while maintaining habitat suitable for migratory birds and travel habitat for the Gulf Coast jaguarundi and ocelot. The Vegetation Management Plan describes short-term and long-term goals to meet this objective. In the short term, the Vegetation Management Plan describes the removal of woody vegetation and invasive species and the post-clearing (initial) revegetation with native herbaceous species. In the long-term, the Vegetation Management Plan describes the maintenance of the vegetation management areas along the Arroyo Colorado Floodway.

The short-term revegetation portion of this plan provides specific direction for post-vegetation removal, erosion prevention measures, seed mixes, planting recommendations (i.e., timing, methods, and conditions), and adaptive management techniques. The focus of the short-term revegetation is to bring the flood design capacity of the channel back into compliance. As such, the species recommended for revegetation are herbaceous species.

The long-term maintenance portion of this plan provides an overview of vegetation control methods within the vegetation maintenance areas. It includes a description of plant species to be controlled (e.g., woody native and non-native species, invasive species) and provides an overview of recommended vegetation control measures, including mechanical vegetation removal and mowing, chemical treatment measures, and a combination of both. All equipment, timing, and qualifications of personnel required to implement each measure are also provided. In addition, the long-term maintenance section of this Vegetation Management Plan addresses sensitive species issues and habitat preservation through temporal and spatial modifications to treatment measures (e.g., no mechanical treatment during bird breeding season, pre-treatment surveys for listed plant

Arroyo Colorado Floodway 1-7 Final November 2015 species in areas of suitable habitat). All logistics for access for vegetation maintenance are addressed, including landowner coordination, regulatory agency coordination, and transportation of personnel, materials, and equipment. The overall purpose of the long-term maintenance portion of this plan is to create habitat suitable to support wildlife use including travel habitat for the Gulf Coast jaguarundi and ocelot while planting vegetation that can be easily maintained to meet the floodway’s design flood conveyance requirements.

1.5 Need for a Vegetation Management Plan

Following all woody vegetative removal activities, it will be necessary for the USIBWC to revegetate the cleared areas along the Arroyo Colorado Floodway using native grass, forbs, and other species to stabilize the channel banks, to maintain the channel’s 21,000 cfs design flood conveyance, and to provide vegetative cover for Federally listed cat species.

Arroyo Colorado Floodway 2-1 Final November 2015

2.0 VEGETATION REMOVAL EFFORTS

The USIBWC reinitiated annual mowing of the Arroyo Colorado Floodway to remove obstructions to flood flows and to maintain design flood conveyance within the channel. Mowing of the floodway controls weed, brush, and tree growth, and is conducted at least once each year.

Farm tractors with 20‐foot rotary mowers are generally used for mowing. Slope mowers are used for vegetation maintenance on the channel banks. Some areas with dense vegetation often require a second mowing. No bulldozers are used for vegetation treatments. Cut‐stump herbicide treatment and hand removal of other invasive woody species (i.e., saltcedar) occur at select locations along the channel.

The USIBWC will continue to remove all woody vegetation from a 50-foot buffer along the Arroyo Colorado Floodway, except within areas where the slope is too steep (i.e., more than 18-degree [°] slope) from Business 77 to FM 509 (see Figure 1-2). In most areas where the buffer is reduced due to steep slopes, the area on the opposite bank is extended to a maximum of 100 feet to compensate for the reduction in buffer. Clearing of approximately 31.6 acres would occur within the Arroyo Colorado Floodway buffer and on one island, and would also include 13.4 acres within the extended areas and an additional 3.6 acres of potential clearing areas.

The USIBWC will mow grass and cut woody vegetation and brush from land rather than from the Arroyo Colorado Floodway channel itself, and where slopes are too steep to use mechanical means of vegetation removal (areas where the slope is greater than 18°), the USIBWC will hand-cut vegetation in order to maintain the channel’s 21,000 cfs design capacity. The USIBWC will use hand equipment including but not limited to chainsaws and weed eaters equipped with metal saw blades to remove the trees and shrubs. All trees and shrubs will be cut at ground level. No cut vegetation will be stockpiled on-site; the biomass will either be mulched on-site using a chipper and dispersed or it will be hauled off-site. The USIBWC will use an all-terrain vehicle (ATV), truck, tractor, backhoe, or similar piece of equipment to haul the biomass off-site. The type of equipment used to haul biomass will be based on site access requirements and limitations.

Stumps of cut trees and shrubs will be treated immediately with an approved herbicide to prevent regrowth, and all herbicides proposed for use will be submitted to the USIBWC for approval prior to use. The manufacturer and State of Texas recommended rate of application for each targeted species will be followed. A State of Texas certified pesticide applicator will supervise all herbicide applications to ensure that only target species are treated and that appropriate herbicides are used.

The USIBWC will only mix herbicides and refill spray equipment in designated staging areas established at a sufficient distance from the Arroyo Colorado Floodway to avoid potential contamination should an accidental spill occur. All spills will be contained and material will be absorbed following standard Best Management Practices (BMPs), such as absorbing small spills with inert materials. All crew members will have the proper personal protective equipment when handling herbicides (e.g., safety glasses, rubber gloves, and long-sleeve shirts and pants). All herbicides will be properly stored and containers disposed of per the manufacturer’s recommendations.

Arroyo Colorado Floodway 2-2 Final November 2015

Although it is not anticipated that herbicide will be applied to open water, all herbicides that are applied will be approved by the U.S. Environmental Protection Agency (EPA) for use in aquatic settings. Such herbicides include Garlon 4 TM or Renovate 3TM (triclopyr) and HabitatTM (imazapyr) (see Section 5.3). Trade names are used for examples only and do not constitute an endorsement of these particular products. Herbicides containing the same chemical formulations as Garlon 4 TM, Renovate 3TM, or HabitatTM would be acceptable, provided they are applied at the same active ingredient rate as the formulation listed.

Staging areas for all equipment will be sited in previously disturbed areas such as unimproved roads, trails, graded areas, or areas with compacted soil that do not support vegetation. Prior to the beginning of work, all crew members will be trained to identify target invasive or undesirable plant species that occur within the area.

Before chemical application, the herbicide application crew will be escorted by the USIBWC’s on-site representative around the entire area and shown the specific locations of “no spray and avoidance areas” (i.e., flagged non-invasive plant areas). All “no spray and avoidance areas” will be monitored for quality assurance during herbicide applications. In addition, a marking dye will be added to the herbicide solution to aid with monitoring and to ensure that overspray into non-target vegetation is minimized. All regulations involving use of herbicides will be followed.

Within target areas along the Arroyo Colorado Floodway, low-growing woody vegetation and herbaceous vegetation will be mowed to approximately 6 to 8 inches in height. A 5-foot corridor of tall grass and other herbaceous plants will remain in the riparian area immediately adjacent to the Arroyo Colorado Floodway channel.

Detailed descriptions of post-clearing revegetation, revegetation methods, and continued vegetation maintenance are provided in Sections 3.0, 4.0, and 5.0, respectively, of this plan.

2.1 Conservation Measures

The USIBWC will include compensation for the woody vegetation loss in consultation with the U.S. Fish and Wildlife Service (USFWS). The USIBWC has previously initiated informal Endangered Species Act Section 7 consultation with the USFWS to explore vegetation removal options and to maintain endangered Gulf Coast jaguarundi and ocelot habitat along the reach in 2014. USIBWC and USFWS staff conducted a site visit on September 25, 2014, and following the visit, the USFWS made the following recommendations:

• Use existing roads and trails as possible to minimize unnecessary vegetation impacts.

• If a new road or trail is needed, minimize its width.

• Use an ATV to haul out trees and minimize the clearing width needed for roads and trails.

• Unintended vegetation damage on the channel bank will be restored with native grass, forbs, and plants to stabilize the banks and provide cover for listed cat species.

• Vegetation disturbance from this project will avoid the general migratory bird nesting period of March through August.

Arroyo Colorado Floodway 2-3 Final November 2015

• A biologist trained in bird identification will survey the areas proposed for disturbance if work will be done during nesting season to avoid the inadvertent destruction of nests, eggs, and young and violation of the Migratory Bird Treaty Act (MBTA).

The USIBWC will continue to coordinate and consult with the USFWS throughout their woody vegetation removal and revegetation efforts.

2.2 Threatened and Endangered Species

Potential habitat for Federally listed and state-listed threatened and endangered plant species may be present within the Project Area (Texas Parks and Wildlife Department 2015). In particular, the Federally listed south Texas ambrosia, Texas ayenia, and star cactus could occur within the Project Area. However, surveys were conducted in September and November 2015 (see Section 1.3;

USIBWC 2015), and no threatened or endangered plant species were observed. Potential habitat for migratory birds and low-quality habitat for the Federally endangered Gulf Coast jaguarundi and ocelot do occur within the Project Area (see Section 1.3; USIBWC 2015) although no protected species were noted during September and November 2015 survey efforts (USIBWC 2015). The potential for the USIBWC to encounter threatened and endangered species within the Project Area during woody vegetation removal operations is low. Even so, if threatened and endangered species are encountered, operations would immediately cease and the USIBWC Environmental Management Division would be contacted to provide further guidance.

Arroyo Colorado Floodway 3-1 Final November 2015

3.0 POST-CLEARING REVEGETATION

Woody vegetation removal and mowing will likely further favor the establishment of non-native and invasive species that are prevalent within the floodway and increase soil compaction, which would reduce plant productivity. To promote the establishment of native vegetative species, all disturbed areas within the approximately 45-acre area along the Arroyo Colorado Floodway between Business 77 and FM 509 will be seeded with an USFWS-approved herbaceous seed mix following mechanical removal of woody vegetation and herbicide application (Figure 3-1). After the initial herbaceous seeding is completed, containerized woody shrub species would be planted within 15 feet of the channel along the banks of the floodway (Figure 3-1).

This section describes all labor, tools, equipment, and materials required for the revegetation of clearing areas (i.e., planting zones) along the Arroyo Colorado Floodway with native plant species.

Three methods could be utilized to apply native herbaceous seed mixes: broadcast seed, drill-seed, and hydro-seed. Broadcast seeding would be the most effective method of application and would be the least expensive. A drill-seed application would be slightly less effective, depending on seasonal rains, but would reduce costs. Hydro-seeding, while often very effective, would be the most expensive method of application.

3.1 Safety and Protection

The USIBWC will perform all work in a safe manner in accordance with all relevant health and safety regulations, including the Occupational Safety and Health Administration (OSHA) standards. The USIBWC will use signage to indicate that riparian use and access will be limited during revegetation activities to limit erosion, minimize damage to vegetation, and provide refuge areas where wildlife can remain undisturbed. Adjacent vegetation, property, structures, and improvements will also be protected from damage.

3.2 Erosion Prevention Measures

Wherever feasible, the USIBWC will chip woody biomass on-site and distribute it as mulch throughout the cleared areas, which would assist in erosion prevention by holding soils in place, retarding rainfall impact, and preserving soil moisture.

Ultimately, native, short woody colony-forming plants, such as Rio Grande dewberry, willow-leaf heimia (Heimia salicifolia), sea oxeye daisy, and sprawling lippia, which would be planted along the floodway, will stabilize the banks from further erosion. These plants are low-growing enough that they should not impede the movement of floodwaters or affect the floodway’s design flood conveyance, and they provide habitat and food sources for smaller mammals and could support Gulf Coast jaguarundi and ocelot.

In cleared areas with steeper slopes greater than 18°, it may be necessary for the USIBWC to use straw wattles to prevent erosion and to limit soil migration off-site. Wattles would consist of man-made cyclinders of compressed natural materials (e.g., straw) that are certified weed and weed-seed free. The straw would be encased in jute, nylon, or other photodegradable materials, and would be approximately 8 to 12 inches in diameter and 20 to 25 feet long. The wattles

Arroyo Colorado Floodway 3-2 Final November 2015

Figure 3-1. Herbaceous and Woody Shrub Species Revegetation along the Arroyo Colorado Floodway Channel

Arroyo Colorado Floodway 3-3 Final November 2015 would be installed in shallow trenches to form a continuous barrier along the contour (across the slope) to intercept water running down the slope and limiting erosion on-site.

Wattles would be installed in woody vegetation areas that require immediate erosion protection, particularly on slopes requiring stabilization until permanent vegetation can be established. Straw wattles would be effective in controlling erosion for one to two seasons, after which time they could be removed from the site or left to degrade in place, since vegetation should be established by this time along the floodway channel.

In addition, in some areas along the Arroyo Colorado Floodway prone to severe erosion, the USIBWC would use commercially produced erosion control blankets. The appropriate erosion control blankets for the area would be wildlife-friendly, loose-weave movable netting composed of biodegradable natural fiber material (Photograph 3-1). Typically these erosion control blankets are composed of coir fiber or rice straw as a base material with jute netting and jute thread. The erosion control blanket will be seed-free and will not contain any weed-seed, tackifiers, or paper products. The specifications of the Curlex I Fibrenet (American Excelsior Company, Arlington, Texas) erosion control blankets are shown in Table 3-1 as an example of a product meeting these specifications.

Photograph 3-1. Curlex I Fibrenet Erosion Control Blanket

(courtesy of American Excelsior Company)

Table 3-1. Curlex I Fibrenet Erosion Control Blanket Specifications Material Content

Fibers Great Lakes Aspen curled wood fibers, approximately 7,000 per square yard

Netting 100 percent biodegradable jute netting with 0.5-inch to 1.0-inch net openings

Arroyo Colorado Floodway 3-4 Final November 2015

To secure erosion control blankets, the beginning of the roll would be placed in a 6-inch by 6-inch anchor trench, the erosion control blankets will be stapled together, the anchor trench will be backfilled, and soil will be compacted. Erosion control blanket edges should overlap by a minimum of 2 inches and blankets should be stapled together. Blankets should not be stretched and must maintain good soil contact. The ends of upslope erosion control blankets will overlap the end of downslope erosion control blankets by a minimum of 6 inches and ends securely stapled.

3.3 BMPs

BMPs are techniques used for control of stormwater runoff, soil stabilization, and sediment control, and are also management decisions designed to prevent or reduce non-point source pollution. The USIBWC will prepare a site-specific Storm Water Pollution Prevention Plan (SWPPP). The SWPPP will address activities such as dust suppression and installation of all necessary water control structures (e.g., silt fencing, straw bales, and wattles). Silt fencing, erosion control blankets, or straw wattles would be applied around each planting zone, as described by the SWPPP, following seed application to mark and protect zones from potential disturbance.

3.4 Timing

Initial seeding of native herbaceous species along the Arroyo Colorado Floodway channel would take place soon after the woody vegetation clearing efforts are completed. In general, herbaceous species, including grasses, perform best within certain temperatures and seasons, and planting outside these times can result in delayed germination or poorer short-term results. However, native grasses can be planted at any time during the year in the Rio Grande Valley if the correct seed mix is selected. For best results, including maximizing germination rates of native grasses and reducing the germination rates of invasive plant species, native grass seeding would take place in late summer or early fall (August 15 – September 30) (Smith et al. 2010).

3.5 Site Preparation

Planting zones would be marked using wire-stake flags to delineate and protect these areas from public entry. In some instances, silt fencing or other appropriate non-intrusive markers may be used to demarcate planting zones. Flagging, or silt fencing, would remain in place until the plants have fully germinated. Seeding areas would be cleared of substantial debris and any other impediments to seed-soil contact.

Site preparation for seeding is as important as timing of planting and seed selection for overall germination success. Prior to seeding, the USIBWC may choose to disc all planting zones with a tractor and discing attachment in order to eliminate glazed surfaces, provide positive surface drainage, and prepare seeding beds. Discing would occur to a maximum depth of approximately 4 inches. Discing would be conducted with two passes of an off-set disk to ensure an even planting surface is provided. The specific type of tractor and disc used is not as important as the results of the discing effort. Discing would be considered sufficient when the soils are free of standing vegetation, lack clumps or clods of soil, and are firm (little to no loose soil) and even. In areas that are not accessible with a tractor and disc, hand tools such shovels, rakes, and hoes can be used.

Arroyo Colorado Floodway 3-5 Final November 2015

If accessibility is possible, a rototiller can be substituted for the use of hand tools to prepare inaccessible areas for planting.

3.6 Seeding Methods and Equipment

Different seeds have varying spread patterns based on their respective weights. Heavier seeds spread further than lighter seeds. This can cause difficulties when heavier and lighter seeds are applied in a mixture. Mixtures dominated by light seeds may require the addition of other material to achieve the proper pounds per acre of seed mix.

Accurate seeding equipment calibration is essential for applying seeds. All seeding equipment would be calibrated as recommended by the manufacturer and seed supplier for the seed types specified.

3.6.1 Broadcast Seed Application (Recommended)

Broadcast seeding is a method of spreading seeds mechanically over a soil surface. Broadcast seeding is especially useful in uneven soil surfaces or poorly prepared soil surfaces. In all cases, broadcast seeding should be followed by dragging or cultipacking (i.e., using a cultipacker, which is a device pulled behind a tractor that rolls over the soils and seeds) operations to ensure soil-seed contact and soil coverage of seeds to reduce bird, small mammal, and insect foraging. The following steps are recommended for broadcast seed application:

• The USIBWC should keep seed in a cool, shaded place until utilized.

• The USIBWC should pull the broadcast seed device at a speed no greater than 3 miles per hour.

• The USIBWC will drag or cultipack all areas where seed was applied to increase seed-soil contact.

3.6.2 Drill-Seed Application

A seed drill is a piece of equipment pulled behind a tractor that sows seeds into the soil and covers the seeds after sowing. Seed drills are often the recommended equipment to use for seeding;

however, they are not necessarily commonly available pieces of equipment and may be difficult to use by those unfamiliar with the seed drill operation. The following steps are recommended for drill-seed application:

• The USIBWC should keep seed in a cool, shaded place until utilized.

• The USIBWC should pull the drill-seed device at a speed no greater than 3 miles per hour.

3.6.3 Hydro-Seed Application

Hydro-seeding is a seed application method that sprays seed and mulch onto the soil surface in the form of a slurry. This method is most applicable to small areas where erosion control needs are greater than the need for revegetation. The following steps are recommended for hydro-seed application:

Arroyo Colorado Floodway 3-6 Final November 2015

• The USIBWC would plan the layout of slurry hose to reduce potential damage to existing native vegetation near each site. Due diligence should be practiced to preserve the newly hydro-seeded areas. Areas furthest from the pump vehicle would be hydro-seeded first and areas nearest to the vehicle would be hydro-seeded last. The slurry hose would be retracted accordingly to minimize trampling and disturbance of newly hydro-seeded areas.

• The slurry should be prepared at the project site as follows:

1. Thoroughly mix water, wood fiber, and tackifier (Table 3-2).

2. Add seed immediately before seeding. Slurry will be completely homogeneous.

3. The slurry will be sprayed with a sweeping motion to produce a uniform mat at the required seeding rate.

Table 3-2. Hydro-Seed Mix Components

Mix Component Rate (pounds/acre)

Water In sufficient quantities to broadcast seed at specified rates Wood Fiber 800 Tackifier 100 Seed At rates specified by manufacturer

3.7 Supplemental Irrigation

Depending on the timing of revegetation efforts and seasonal rainfall, irrigation supplied by the natural rainfall cycle will be sufficient to provide water for the remainder of the project’s life.

Supplemental irrigation on native grass seeds often forces early germination of native grasses, causes shallow rooting of native grasses, and improves the germination rates of invasive species with seeds in the seedbank.

Where rapid germination of native grasses and other herbaceous plant species is needed for erosion control measures, the USIBWC, at their discretion, may choose to occasionally supplement rainfall with irrigation. If the USIBWC decides to provide supplemental irrigation to specific zones, the water would be supplied via a water truck. The USIBWC would use hoses to connect to coupling valves on the water truck. The USIBWC would arrange and move portable impact rotors to evenly apply water per irrigation event. It is critical that the USIBWC keep the surface soil moist until germination has occurred. Then, the frequency would be lessened, but irrigation rates would be increased to aid in deeper root growth for establishment. The USIBWC would have erosion control measures installed in order to prevent runoff during irrigation events.

3.8 Materials Specifications

The broadcast seed method is recommended for the revegetation along the floodway. However, each method is described above to provide a set of options that best fit the approved budget, equipment availability, time frame, and vegetation establishment requirements. It is also recommended that a field environmental monitor supervise all revegetation activities.

Arroyo Colorado Floodway 3-7 Final November 2015

All plant materials used for revegetation will be derived, if possible, from populations of non-woody native species found either on-site or as close to the local area as possible. As practicable, non-woody native plants will be left in place during woody vegetation removal or salvaged from clearing areas and temporarily stored whenever possible for use in native plant revegetation areas.

The on-site field environmental monitor will be responsible for identifying native plants to be left undisturbed and for flagging areas to denote locations of native plants.

The USIBWC will make every effort to obtain seed from a local Lower Rio Grande Valley native seed vendor to ensure the use of local ecotypes. Vendors outside of the Lower Rio Grande Valley may be used if project timing does not coincide with seed availability from the local vendors, but all vendors shall be approved by the Environmental Management Division.

3.9 Seed Mixes

Seed mixes will be procured from a commercial vendor. The vendor will supply the USIBWC with the USFWS and Natural Resources Conservation Service (NRCS)-recommended pounds per acre of pure live seed (PLS) and species mixture percentages. For restoration and revegetation projects within the Rio Grande Valley, the USFWS typically recommends a seeding rate of 2 PLS/1,000 square feet. The USIBWC will continue to coordinate with the USFWS to ensure that the agency concurs with the recommended PLS. All seeds will be from a fresh, clean, new crop that is mixed by the vendor and packaged in the vendor’s unopened container with the original labeling. The obtained seed will be labeled as “certified” under the Texas Agriculture Code. Seed will meet the requirement of the Federal Seed Act and the Texas Seed Law, including the labeling requirement for showing PLS (PLS = purity x germination), name, and type of seed. Within the clearing areas to be planted, the USIBWC will scarify all the areas cleared of vegetation to eliminate glazed surfaces, provide positive surface drainage, and prepare seeding beds.

Based on other successful revegetation efforts along the Arroyo Colorado Floodway in the vicinity of clearing areas and in other regions of south Texas (Smith et al. 2010), a seed mix of annuals and perennials that do well in floodplain soils will be seeded within the Arroyo Colorado Floodway.

The seed mix would include fast germinating native grasses, as well as native herbaceous species that germinate and establish more slowly over time. Commercially available native seed mixes provide the greatest success at the lowest cost, and the USIBWC should procure a native seed mix composing a subset of native species listed in Table 3-3 from a local certified grower of south Texas native plants.

Table 3-3. Native Herbaceous Plants to Include in Seed Mix Common Name Scientific Name

Black-eyed Susan Rudbeckia hirta Climbing milkweed Funastrum cynanchoides

Cutleaf daisy Erigeron compositus Dilley germplasm slender grama Bouteloua repens

Divot tallow weed blend Hybrid of Plantago hookeriana and Plantago rhodosperma Giant coneflower Rudbeckia maxima Green sprangletop Leptochloa dubia

Arroyo Colorado Floodway 3-8 Final November 2015

Common Name Scientific Name Hairypod cowpea Vigna luteola

Illinois bundleflower Desmanthus illinoensis Little head gum weed Grindelia microcephala

Many-spiked flat sedge Cyperus polystachyos Mariah germplasm hooded windmillgrass Chloris cucullata

Maximilian sunflower Helianthus maximiliani Nealley’s sprangletop Leptochloa nealleyi Pearl netleaf milkvine Matelea resticulata Pink evening primrose Oenothera speciosa

Pitcher sage Salvia spathacea Plains coreopsis Coreopsis tinctoria

Scarlet sage Salvia splendens Sea oxeye daisy Borrichia frutescens

Texas signalgrass Urochloa texana Welder germplasm shortspike windmillgrass Hybrid of Chloris cucullata and Chloris verticillata Zapata germplasm Rio Grande clammyweed Polanisia dodecandra ssp. riograndensis

3.10 Water

If supplemental irrigation is used, it should be suitable for agricultural use and be free of harmful substances that would adversely affect plant growth or vigor. The USIBWC would test the water source’s pH prior to application. If test results show that the water source is alkaline (above a pH of 8) or acidic (below a pH of 5), the USIBWC would buffer water to a neutral pH of 6 or 7.

3.11 Straw

Straw material would be derived from irrigated cropland and certified weed and weed-seed free.

Straw pieces would be at least 4 inches long, but preferably 6 inches or longer. Straw should not contain noxious weeds, glass, plastic, metal, rocks, or other inorganic material. Straw should not have been previously used.

3.12 Tackifier

Tackifier would be non-asphaltic, non-toxic to plant and wildlife, and non-staining to rock surfaces. Tackifier would be in powder form, may be re-emulsifiable, and would be a processed organic adhesive derivative of Plantago insularis used as a soil binder.

Arroyo Colorado Floodway 3-9 Final November 2015

3.13 Wood Fiber

Wood fiber used for these efforts would be derived from wood chips or similar wood material generated on-site and distributed in an even layer.

3.14 Equipment and Tools

The following equipment would be used to scarify soil, broadcast seed mixes, and to install erosion control devices, as needed:

• Broadcast seeding would use a commercial broadcast seeder with multiple seed boxes allowing variable seed sizes. Broadcast seeders may be mounted on ATVs, tractors, tillage tools, or other implements.

• Drill seeders would have multiple seed boxes allowing variable seed sizes. Drill-seeders may be mounted on all ATVs, tractors, tillage tools, or other implements.

• Hydro-seeding would use a commercial hydro-seeder that has a built-in agitation system with the capacity to continuously agitate, suspend, and homogeneously mix the slurry.

• Tractor with the capacity to pull discing, dragging, and cultipacker attachment.

• Commercial mechanical straw blower capable of being mounted on ATVs, tractors, tillage tools, or other implements.

• Water truck would be outfitted with components to connect to an irrigation system’s portable impact rotors.

• Specialized tacking equipment used to apply tackifier slurry over seed bed.

• Standard 4-gallon backpack sprayers used for herbicide applications.

3.15 Adaptive Management Techniques

Following initial revegetation efforts, the USIBWC would monitor seed sprout on a monthly basis.

The USIBWC would inspect all seeded areas for failures and make necessary repairs. If after 1 year, native species included in the seed mix do not account for 20 percent of the cover in the clearing areas, the USIBWC would reseed areas within the planting season.

In addition to monitoring the growth of seeded herbaceous species, during non-growing seasons, the USIBWC would monitor erosion and apply interim surface stabilization methods, such as additional mulching or straw wattles, to control surface erosion.

The USIBWC would also treat with the recommended herbicides invasive woody species (see Section 4.4) that colonize the seeded clearing areas. All herbicides would be applied by a State of Texas licensed pesticide applicator. The USIBWC would use chainsaws, in association with chemical treatment of cut stumps, to remove invasive woody species and to prevent re-sprouting.

Arroyo Colorado Floodway 4-1 Final November 2015

4.0 LONG-TERM VEGETATION MAINTENANCE

One of the critical steps after planting of herbaceous plants is maintenance and monitoring of all seeded areas. Further, containerized plants of native shrubs will be planted within 15 feet of the Arroyo Colorado Floodway channel banks to improve habitat conditions for the Gulf Coast jaguarundi and ocelot (Figure 4-1). Maintenance of each zone would ensure that final success criteria (see Table 5-2) are met. The maintenance and monitoring would be ongoing for a 5-year period.

Monitoring of native species percent cover (see Section 5.0) would be used to evaluate the success of each zone. Information from the monitoring program would direct maintenance activities or techniques to ensure the success of the revegetation in an adaptive management approach. The maintenance phase may be revised based on the results of annual monitoring reports, provided the revisions improve the chances of the final success criteria being met or exceeded. The primary tools used by the USIBWC for continued vegetation maintenance would include mowing, mechanical removal of woody species resprouts, and direct herbicide application to specific invasive plant species. Additional potential maintenance could include the following:

• annual over-seeding with native species

• replanting of native woody shrub species

• supplemental irrigation

• reducing or preventing human/mechanical intrusion

• repairing demarcating markers (i.e., silt fencing, wire flagging, or other appropriate non-intrusive markers)

4.1 Containerized Plantings

To create wildlife habitat and to stabilize banks, it is recommended that containerized native shrubs be planted along the Arroyo Colorado Floodway following the germination of native herbaceous plants from seeding operations. Shrubs will be low-growing species (up to 3 feet in height) that can withstand periodic mowing and that will not impede flood flows or collect debris. Table 4-1 provides suitable native woody plant species to be planted within 15 feet of the bank of the Arroyo Colorado Floodway.

Table 4-1. Recommended Containerized Native Shrub Plantings Common Name Scientific Name Container Size On-center Spacing for Planting Carolina wolfberry Lycium carolinianum 4-inch 4-foot

Devil’s-claw Pisonia aculeata 4-inch 4-foot Leather leaf Maytenus phyllanthoides Gallon 8-foot

Mexican buttonbush Cephalanthus salicifolius Gallon 8-foot Primrose willow Ludwigia octovalvis 4-inch 4-foot

Rio Grande butterfly bush Buddleja sessiliflora 4-inch 4-foot Rio Grande dewberry Rubus riograndis 4-inch 4-foot

Sprawling lippia Lippia alba 4-inch 4-foot Willow-leaf heimia Heimia salicifolia Gallon 8-foot

Arroyo Colorado Floodway 4-2 Final November 2015

Figure 4-1. Conceptual Diagram of Revegetation with Herbaceous and Woody Shrub Species along the Arroyo Colorado Floodway Channel

Arroyo Colorado Floodway 4-3 Final November 2015

Native shrubs would be procured from a local commercial vendor specializing in the propagation and growth of native plant species. Plant material would come from propagules collected from the Arroyo Colorado Floodway or Lower Rio Grande Valley. On-center spacing is provided in Table 4-1. As appropriate, recommendations and modifications to spacing can be made to best field-fit plantings.