Old Channel of the Comal River Riparian Vegetation Plan

Prepared for:

City of New BraunfelsJune 6, 2013

Prepared by: FREESE AND NICHOLS, INC.

10814 Jollyville Rd. Building 4, Suite 100 Austin, Texas 78759

(512) 617-3100

NEB13133

(Attachment 11)

TABLE OF CONTENTS

1.0 INTRODUCTION .................................................................................................. 1 2.0 METHODOLOGY .................................................................................................. 2 3.0 SITE ASSESSMENT RESULTS ........................................................................... 3

3.1 Field Assessment ........................................................................................................ 3 3.2 Recommendations ..................................................................................................... 7

4.0 CONCLUSIONS ................................................................................................... 10 5.0 REFERENCES ..................................................................................................... 11

LIST OF TABLES

Table 3.1 Invasive vegetation types in the herb sections. ...................................................................................... 3 Table 3.2 Native riparian re-vegetation suggestions................................................................................................ 8

LIST OF FIGURES

Figure 3.1 Photograph of dense elephant ear thicket. ............................................................................................. 4 Figure 3.2 Photograph of Chinese tallow thicket. ...................................................................................................... 5 Figure 3.3 Photograph of wax-leaf ligustrum thicket. .............................................................................................. 5 Figure 3.4 Photograph of dense giant reed. .................................................................................................................. 6 Figure 3.5 Photograph of four o’clock patch. ............................................................................................................... 6 Figure 3.6 Photograph of cedar elm tree lying over a live oak tree. ................................................................... 9

ATTACHMENTS

Attachment 1- Map of Invasive Vegetation Attachment 2- Map of Trees

(Attachment 11)

1.0 INTRODUCTION

Freese and Nichols, Inc. environmental scientists, Patrick Garnett and Meredith Heather,

performed a site visit to the “Old Channel” of the Comal River in Landa Park. This section of

the river is being studied for bank stabilization with the riparian vegetation plan being one

effort of the study. The site visit allowed Mr. Garnett and Ms. Heather to observe the bank

vegetation and erosion and make suggestions for riparian stabilization. The term riparian refers

to the land along the bank of the river. Areas along the bank were determined where

vegetation can remain in its present condition and where invasive vegetation needs to be

removed or replaced by native riparian vegetation. Riparian vegetation recommendations were

selected to protect the bank and look aesthetically pleasing in areas not receiving structural

improvements.

During previous efforts of this study, the native and invasive vegetation was catalogued for

purposes of developing a remediation plan for this stretch of the river. The fluvial

geomorphological conditions of the river were evaluated for current and possible bank failures

including erosion and incising. Structural concepts will be developed in areas where vegetation

stabilization will not be sufficient enough due to bank steepness. All efforts of this study will

come together to help provide a more stable bank along the “Old Channel” of the Comal River

in Landa Park.

(Attachment 11)

2.0 METHODOLOGY

During the site visit, Mr. Garnett and Ms. Heather walked along the bank of the Comal River in

Landa Park evaluating and recording the current riparian vegetation. Using a Trimble GPS, the

areas with invasive vegetation were mapped and named as “Herb Sections.” GPS points were

taken at native trees that were greater than eight inches in diameter at four and one-half feet

above the ground (DBH). Recommendations were then made regarding native vegetation to

remain and invasive vegetation to be removed and/or replaced.

(Attachment 11)

3.0 SITE ASSESSMENT RESULTS

3.1 FIELD ASSESSMENT

Both sides of the channel have growths of invasive vegetation. The invasive herb sections

recorded during the site visit are described in Table 3.1.

Table 3.1 Invasive vegetation types in the herb sections. Herb Section Invasive Vegetation Type Square Footage

Herb 1 Elephant ear (Xanthosoma sagittifolium); Chinese tallow (Sapium sebifera)

164

Herb 2 Elephant ear 475 Herb 3 Elephant ear 205 Herb 4 Elephant ear 427 Herb 5 Elephant ear; Wax-leaf

ligustrum (Ligustrum japonicum)

502

Herb 6 Giant reed (Arundo donax) 368 Herb 7 Elephant ear 148 Herb 8 Elephant ear; Chinese tallow 101 Herb 9 Elephant ear; Chinese tallow 32 Herb 10 Elephant ear; Chinese tallow 1000 Herb 11 Elephant ear 430 Herb 12 Four o’clock (Mirabilis jalapa) 2570 Herb 13 Chinese tallow 3033

(Attachment 11)

Along the right bank, the herb sections consist of thickets of invasive elephant ear (Xanthosoma

sagittifolium) and Chinese tallow (Sapium sebifera), shown in Figures 3.1 and 3.2, respectively.

The herb sections along the left bank are dense with elephant ear, wax-leaf ligustrum

(Ligustrum japonicum), Chinese tallow, and giant reed (Arundo donax). Wax-leaf ligustrum and

giant reed thickets are shown in Figures 3.3 and 3.4, respectively. The right bank also has a

large patch of invasive four o’clock (Mirabilis jalapa), shown in Figure 3.5. Herb 10, 11, and 13

lie on a peninsula and are thick with elephant ear and Chinese tallow. The herb sections,

mapped out in polygons, are displayed in Attachment 1, following the report.

Figure 3.1 Photograph of dense elephant ear thicket.

(Attachment 11)

Figure 3.2 Photograph of Chinese tallow thicket.

Figure 3.3 Photograph of wax-leaf ligustrum thicket.

(Attachment 11)

Figure 3.4 Photograph of dense giant reed.

Figure 3.5 Photograph of four o’clock patch.

(Attachment 11)

3.2 RECOMMENDATIONS

It is the opinion of FNI environmental staff that the following invasive vegetation be removed

along the right bank: four o’clock, wax-leaf ligustrum, and Chinese tallow (Attachment 1, Table

3.1). When removing the trees, it is beneficial to cut them down to a stump and leave the

roots in place to aid in erosion control and stabilization of the bank. To help inhibit regrowth of

the invasive trees, the trunks can be sprayed with a forestry herbicide. It is suggested to cut the

stump as close to the ground as possible and to apply the herbicide quickly after cutting.

Triclopyr products are more effective and reliable at controlling regrowth (Langeland). The

recommended salt formulation of triclopyr, called Garlon 3A®, is water-soluble and with

adequate sunlight may degrade in several hours, but it is slightly toxic to fish and aquatic

invertebrates. However, if applied properly, triclopyr should not be found in concentrations

adequate to kill aquatic organisms (Tu et al. 2001). The ester formulation, Garlon 4®, is not

soluble in water, can take significantly longer to degrade, and can be extremely toxic to fish and

aquatic invertebrates. Both formulations are relatively non-toxic to terrestrial vertebrates and

invertebrates.

Along the left bank, it is FNI’s suggestion to remove the invasive thicket of wax-leaf ligustrum in

Herb 5 and the giant reed in Herb 6 (Attachment 1). These sections can then be re-vegetated

with native plants listed below in Table 3.2. There is a cedar elm (Ulmus crassifolia) lying over a

live oak (Quercus virginiana) that is leaning out over the river. These two trees, shown in Figure

3.6, should both be removed. The locations of the recorded trees, suggested to be kept and the

two to be removed, are displayed in Attachment 2.

Native riparian vegetation that is currently growing along both banks and would be beneficial to

keep for canopy cover are sycamore (Platanus occidentalis), pecan (Carya illinoinensis), and box

elder (Acer negundo). Favorable ground cover to keep are frostweed (Helianthemum spp.),

Virginia rye (Elymus virginicus), Turk’s cap (Malvaviscus arboreus), and straggler daisy

(Calyptocarpus vialis). Both banks have thickets of the invasive elephant ear. It is FNI’s

(Attachment 11)

recommendation to remove the elephant ears and replace them with native vegetation such as

arrowhead (Sagittaria lancifolia) and horsetail (Equisetum hyemale).

The riparian vegetation listed in Table 3.2 are suggestions made by FNI environmental staff in

the event of re-vegetating the banks, either after the removal of invasive vegetation or the

construction of the terraced wall along the bank. The plants listed are native and grow well in

riparian areas.

Table 3.2 Native riparian re-vegetation suggestions.

Common Name Scientific Name Squarestem spikerush Eleochris quadrangulata Indian wood-oats Chasmanthium latifolium Arrowhead Sagittaria lancifolia Virginia wild rye Elymus virginicus Straggler daisy Calyptocarpus vialis Frog fruit Phyla nodiflora White mistflower Ageratina havanensis Turk’s cap Malvaviscus drummondii Southern dewberry Rubis trivialis Cedar sage Salvia roemeriana Mountain laurel Sophora secundiflora Scouring rush horsetail Equisetum hyemale Common three-square rush Schoenoplectus pungens

(Attachment 11)

Figure 3.6 Photograph of cedar elm tree lying over a live oak tree.

(Attachment 11)

4.0 CONCLUSIONS

Based on field observations, portions along the banks along the Comal River in Landa Park are covered

with invasive riparian vegetation. As one effort in the bank stabilization study of the Old Channel of the

Comal River, recommendations were made for the removal and/or replacement of invasive vegetation

with native riparian vegetation. The native vegetation recommended is expected to grow well in

riparian areas and have good root structures to help with erosion control. The native trees and

vegetation proposed to be kept along the banks will offer beneficial canopy and ground cover along the

banks. With their deep roots already in place, they will continue to help stabilize the bank.

As plans develop for bank stabilization and possible structural concepts, further discussions should be

held regarding the different areas of the banks. More detailed recommendations can be made by FNI

environmental staff concerning the areas intended to be re-vegetated once design alternatives are

selected.

(Attachment 11)

5.0 REFERENCES

Langeland, K.A. (2006). Herbicides to Kill Invasive Trees in Home Landscapes. Institute of

Food and Agricultural Sciences, University of Florida. Retrieved June 3,

2013. http://edis.ifas.ufl.edu/ag259.

Tu, M., Hurd, C., Robison, R., & Randall, J.M. “Triclopyr.” Weed Control Methods Handbook,

The Nature Conservancy (2001): 7k.1-7k.6

(Attachment 11)

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