Watershed Protection Plan - Lower Rio Grande Valley Development ...

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POLLUTION IN THE ARROYO COLORADO According to the Phase I TMDL study of the Arroyo Colorado, between 1989 and 1999, urban storm water in the Arroyo Colorado watershed accounted for the following portion of pollutant loads: • 26% of the BOD • 9% of the ammonia nitrogen • 7% of the nitrate nitrogen • 6% of the orthophosphate • 10% of the sediment Industrial Activity Sources of pollution to the Arroyo Colorado include releases of concentrated fertilizer and raw sugar during barge off-loading and loading operations at the Port of Harlingen and at similar facilities located near the port and city of Rio Hondo. In addition to the spillage of dry fertilizer and raw sugar directly into the Arroyo Colorado, these facilities may also be contributing pollutants to the Arroyo Colorado from stormwater runoff. The magnitude of pollutant contributions from these operations has not been quantifi ed but may be substantial. The spillage and runoff of dry fertilizer and raw sugar occurs in the portion of the Arroyo Colorado identifi ed as the Zone of Impairment, where the highest incidence of low dissolved oxygen occurs in the Arroyo Colorado. Raw sugar being loaded into barges at the Port of Harlingen Off-loading commercial dry fertilizer at the Port of Harlingen The Role of Physical Modifications The Arroyo Colorado is a constructed fl oodway through approximately half of its course in southern Hidalgo County. Between 1932 and 1947, the IBWC built fl ood levees and converted the main channel of the Arroyo Colorado into a pilot channel designed to convey low fl ow drainage and fl oodwaters from the Rio Grande Valley. Between 1945 and 1951, the USACE dredged and straightened the tidal portion of the Arroyo Colorado, widening an area near Harlingen to accommodate barge traffi c from the Laguna Madre to the Port of Harlingen. These two large-scale physical modifi cations limit the Arroyo Colorado’s ability to assimilate pollutants naturally and meet the uses designated by the State of Texas. The designed fl ow velocity of the pilot channel in the Main Floodway (i.e., the Arroyo Colorado above Tidal in southern Hidalgo County) is signifi cantly higher than the slow movement of water that normally occurs in oxbow lakes and other types of natural resaca systems. High fl ow velocities create an unstable, erosional regime in a coastal stream like the Arroyo Colorado. Adding to the instability of the Arroyo Colorado is the loss of sinuosity in the main channel from rectifi cation and channelization and a lack of adequate riparian vegetation to protect the banks from erosion. Stream instability helps keep suspended sediment Arroyo Colorado Watershed Protection Plan 60 January 2007
POLLUTION IN THE ARROYO COLORADO Storm Drain loads high in the Arroyo Colorado, and high suspended sediment prevents the Arroyo Colorado from assimilating nutrients along its course. Under normal conditions, ammonia and nitrates are removed by algae, which use these nutrients to grow. However, algal growth is suppressed when sediment loads are high because light penetration limits photosynthesis. Also, suspended sediments help to transport phosphate, another important nutrient, by adhering to it and releasing it downstream. The lack of an adequate riparian habitat can also help keep dissolved oxygen levels lower in a stream by keeping surface water temperatures higher. Oxygen gas stays dissolved in water better at cooler temperatures. The canopy offered by trees and other riparian vegetation shade the banks Llano Grande Lake of natural streams, helping to keep surface water temperatures lower, and thereby increasing the solubility of oxygen. Dredging in the tidal portion of the Arroyo Colorado also contributes signifi cantly to the stream’s inability to meet the State’s Water Quality Standards for a high aquatic life use. The removal of bottom sediments from the bed of the Arroyo Colorado results in the deep intrusion of hypersaline (very salty) water from the Laguna Madre to the Port of Harlingen. The intrusion of salt water this far inland causes the upper and lower portions of the water column of the Arroyo Colorado to segregate into distinct density layers that do not mix well vertically; this phenomenon is known as density stratifi cation. During periods of low fresh water fl ow and warm temperatures, the bottom depths (~3m) of the water column in much of the tidal segment of the Arroyo Colorado become almost completely depleted of oxygen (0-1.5 mg/l), leaving a surface layer of less than one meter with adequate conditions for aquatic life (DO between 4-6 mg/l). Natural aeration (i.e., oxygenation) in coastal streams is largely dependent on wind action. Oxygen is introduced into the surface layers of coastal water bodies through mechanical agitation caused by wind movement. Wind aeration can be inhibited in stream January 2007 61 Arroyo Colorado Watershed Protection Plan
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Photos courtesy of Brand Cowan, Cam
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CONTENTS ACKNOWLEDGEMENTS .........
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CONTENTS - FIGURES Habitat Restorat
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TABLES LIST OF TABLES Table 1. Tabl
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EXECUTIVE SUMMARY The Arroyo Colora
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EXECUTIVE SUMMARY Habitat Approxima
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EXECUTIVE SUMMARY management practi
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EXECUTIVE SUMMARY Elements of the W
Page 22 and 23: INTRODUCTION In its most pristine c
Page 24 and 25: INTRODUCTION Colorado, where physic
Page 27 and 28: THE ARROYO COLORADO WATERSHED PARTN
Page 34 and 35: THE ARROYO COLORADO WATERSHED The A
Page 36 and 37: THE ARROYO COLORADO WATERSHED the D
Page 38 and 39: THE ARROYO COLORADO WATERSHED Figur
Page 40 and 41: THE ARROYO COLORADO WATERSHED Table
Page 42 and 43: THE ARROYO COLORADO WATERSHED Resac
Page 45 and 46: STATE OF THE WATERSHED From a natur
Page 47 and 48: STATE OF THE WATERSHED resacas loca
Page 49 and 50: STATE OF THE WATERSHED Water Qualit
Page 51 and 52: STATE OF THE WATERSHED Table 8. Des
Page 53 and 54: STATE OF THE WATERSHED Figure 12. L
Page 55 and 56: STATE OF THE WATERSHED Figure 14. 1
Page 57 and 58: STATE OF THE WATERSHED Figure 18. T
Page 59 and 60: STATE OF THE WATERSHED Figure 20. T
Page 61 and 62: STATE OF THE WATERSHED facilities a
Page 63 and 64: STATE OF THE WATERSHED controlled.
Page 65 and 66: STATE OF THE WATERSHED Tree plantin
Page 67 and 68: XXX Arroyo Colorado Watershed Prote
Page 69 and 70: POLLUTION IN THE ARROYO COLORADO
Page 71: POLLUTION IN THE ARROYO COLORADO 1)
Page 76 and 77: INSTITUTIONAL FRAMEWORK Successful
Page 78 and 79: INSTITUTIONAL FRAMEWORK the water r
Page 80 and 81: INSTITUTIONAL FRAMEWORK managing pr
Page 82 and 83: INSTITUTIONAL FRAMEWORK criteria fo
Page 84 and 85: INSTITUTIONAL FRAMEWORK pertaining
Page 87 and 88: ELEMENTS OF THE ARROYO COLORADO WAT
Page 102 and 103: EDUCATION AND OUTREACH Fostering lo
Page 104 and 105: EDUCATION AND OUTREACH • Distribu
Page 106 and 107: EDUCATION AND OUTREACH quality prob
Page 108 and 109: EDUCATION AND OUTREACH • Develop
Page 110 and 111: EDUCATION AND OUTREACH take to do t
Page 112 and 113: EDUCATION AND OUTREACH industry, de
Page 114 and 115: EDUCATION AND OUTREACH To support m
Page 116 and 117: EDUCATION AND OUTREACH members of t
Page 119 and 120: ESTIMATED WATERSHED LOADINGS AND LO
Page 121 and 122: ESTIMATED WATERSHED LOADINGS AND LO
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ESTIMATED WATERSHED LOADINGS AND LO
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WATER QUALITY MONITORING PLAN Figur
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WATER QUALITY MONITORING PLAN Figur
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WATER QUALITY MONITORING PLAN Autom
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TECHNICAL AND FINANCIAL ASSISTANCE
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SOURCES OF TECHNICAL AND FINANCIAL
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IMPLEMENTATION SCHEDULE Federal CWA
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IMPLEMENTATION SCHEDULE Table 24. T
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IMPLEMENTATION SCHEDULE TMDL Monito
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MEASURING PROGRESS The ultimate mea
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MEASURING PROGRESS Table 25. Criter
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MEASURING PROGRESS Table 27. Milest
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APPENDICES HUC HWWS IBWC IMAS km LL
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APPENDICES APPENDIX B Arroyo Colora
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APPENDICES arise necessitating the
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APPENDICES c. Committee Members: Co
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APPENDICES APPENDIX C Arroyo Colora
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APPENDICES FRANK MARTINEZ IBWC JAME
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APPENDICES WESLEY ROSENTHAL TAMU JE
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APPENDICES APPENDIX E Rare Plants a
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APPENDICES Common Name Scientific N
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APPENDICES APPENDIX F Locally Activ
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APPENDICES Gorgas Science Foundatio
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APPENDICES Endangered Species Act T
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APPENDICES APPENDIX H List of Feder
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APPENDICES Common Name Scientific N
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APPENDICES APPENDIX I Selected Mars
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APPENDICES Mid-Depths - 15 to 50 cm
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REFERENCES Arnold, J.G., P.M. Allen
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REFERENCES IBWC, 2003. Hydraulic Mo
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REFERENCES TAES (Texas Agricultural
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REFERENCES USEPA, 1999. Draft Guida
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