Mark WILLIAMS, Ira ARTZ, Krey PRICE

Transcription

1 Restoring Ecosystem Habitat in the Arid Southwestern United States: Lessons Learned Mark WILLIAMS, Ira ARTZ, Krey PRICE Tetra Tech, Inc. United States

2 Ecosystem Restoration in the United States Since 1986, the agency most responsible for providing large-scale, ecosystem restoration projects in the US has been the US Army Corps of Engineers Civil works projects for restoration often $100 s of millions of dollars, with the Everglades costing into the $billions. Tetra Tech has been fortunate to provide support for many restoration projects, especially in the arid Southwestern U.S.

3 Problems in the Arid Southwest Dryland Rivers Hyper-arid environment Southwestern U.S. annual precipitation < cm Evapotranspiration > 100 cm NRCS

4 Problems in the Arid Southwest Even though riparian areas represent <1% of the region s area, they support > 50% of the nesting bird species and >75% of vertebrate wildlife species (Johnson et al., 1977, and Gillis, 1991).

5 Problems in the Arid Southwest Ecosystems like this used to be much more common Prior to dam construction and groundwater overdraft, many streams were perennial The meandering channels included sandbars and backwaters.

6 Problems in the Arid Southwest Cottonwoods, willows, mesquite forests, and cienegas used to fill the floodplain.

7 Problems in the Arid Southwest Degradation caused by upstream dams, drought, climate change, and urban impacts such as groundwater overdraft, floodplain encroachment, habitat loss, modified hydrology, landfills, mining, invasive species, bank stabilization and channelisation USGS Arizona stream: 1904 and recent

8 Problems in the Arid Southwest Lack of vegetation leads to unstable banks, as shown here in 1978 flood event on the Rillito River 70 m of lateral channel migration USGS

9 Problems in the Arid Southwest USGS The southwest has become increasingly urbanised Restoration of riparian ecosystems in the Sonoran Desert considered critical by the Nature Conservancy

10 Opportunities for Restoration The Corps of Engineers and local municipalities have cost-shared several ecosystem restoration studies in the Phoenix and Tucson areas, in Arizona USGS

11 New Mexico Phoenix Gila River Watershed Tres Rios Opportunities for Restoration Verde River Watershed Utah Flagstaff Rio Salado ARIZONA Salt River Watershed Tucson Tetra Tech s role has been to provide planning, economic and environmental analysis, and design support to 3 major projects in the 34,000 square kilometer Salt River watershed, in the Phoenix metropolitan area, Arizona Va Shly ay Akimel

12 New Mexico Opportunities for Restoration Project benefits include the following categories: Habitat creation and restoration Removal of invasives Restoration of gravel pits Restabilisation of the geomorphic regime Water supply through infiltration Flood risk management Recreation

13 New Mexico Restoration Objectives Restoration of a more natural riverine environment: Return ecosystem functions Return species diversity Replace lost riparian habitat Scrub-Shrub Mesquite Mesquite Cottonwood Bosque Wetland Willow Ponded Flow Wetland Cottonwood Willow

14 Avg Annual Costs ($1,000) New Mexico Lesson Learned The challenge in developing a restoration plan is finding the most cost efficient yet effective solution Federal water resource guidelines are strict on economic benefit/cost analyses Relies on comparing a multitude of possible measures Combined into alternatives Rio Salado Oeste Without Project Equivalent Annual Damages (in $1,000s) Reach Structure & Content Cleanup Temp. Housing Total 2L $ 42 $ 10 $ 0.4 $ 52 3L $ 2 $ 1 $ 0.1 $ 3 4L $ 2 $ - $ 0.1 $ 2 5L $ 27 $ 4 $ 0.9 $ 32 6L $ 11 $ 3 $ 0.1 $ 14 Total - S. of River $ 84 $ 18 $ 1.6 $ 104 $16,000 $14,000 $12,000 $10,000 $8,000 $6,000 Rio Salado Oeste Incremental Analysis Alt 4 Alt 5 Alt 5B Alt 5A 5R $ 123 $ 5 $ - $ 128 6R $ 4 $ 0.5 $ - $ 5 Total - N. of River $ 127 $ 6 $ - $ 133 Total $ 211 $ 24 $ 2 $ 236 Notes: Damages for Reaches Not Shown are Minimal $4,000 $2,000 $0 Alt AAFCU's

15 New Mexico Cost Effectiveness Analysis Use of IWR-Plan Incremental analysis program Analyzes thousands of possible combinations of potential features Cost inputs compared to habitat units outputs Results in best-buy and optimised plans Used nationwide

16 Monetary Costs Cost Effectiveness Analysis 20,000 18,000 NOT Cost Effective 16,000 14, B 5A 12,000 10,000 Refine 2 8, , , , Benefits: Habitat Units Best Buy

17 New Mexico Tres Rios Project Located where three rivers meet ( Tres Rios ): the Salt, the Gila, and the Agua Fria The project began as a means of treating treatment plant effluent using constructed wetlands The Plan Formulation analysis justified a 10-km, $110 million restoration project

18 Tres Rios IN CONSTRUCTION. SPONSORS: City of Phoenix/Gila River Indian Community $110 M 11 river kilometers Restoration (600 ha) Levee (100-year) Recreation/education Cultural mitigation

19 91 st Avenue Flood Control Levee Tres Rios Project Plan Overview Overbank Wetlands N Open Water Marshes Riparian Corridors Flow Regulating Wetlands (see next slide)

20 Flow Regulating / Constructed Wetlands

21 New Mexico Flow Regulating / Constructed Wetlands Wetlands even out diurnal treatment plant peaks for more uniform treatment in constructed wetlands Outflow then piped along top of bank with flow outlets into the overbank wetlands USACE Stormwater Channel Overbank Wetlands (OBW) FRW 1 FRW 1 DW A FRW 2 DW B FRW 3 Effluent Channel Force Mains FRW Inlet Structure Discharge Structure Salt River Emergent Zone/Hummocks Open (Deep) Water Road/Maintenance Access Island

22 Riparian Corridors

23 Open Water Marsh

24 Overbank Wetlands OVB - NORTH OBW CULVERTS DISCHARGE SPILLWAY OVB-NORTH USACE PIPE INLET DISCHARGE SPILLWAY OVB-SOUTH USACE - LEVEE SALT RIVER OVB - SOUTH Total Length = 2743 m Total Area = 52 ha Aquatic = 4.5 ha Riparian = 6.8 ha Dimensions Floodplain Terrace = 5.8 ha EFFLUENT CHANNEL Wetland = 32.6 ha Mesquite = 2.3 ha SALT RIVER AUXILLARY DISCHARGE

25 New Levee Alignment

26 Va Shly ay Akimel Historic Condition: Perennial water High water table Braided & meandering Cottonwood/willow, mesquite communities Braided and meandering

27 Va Shly ay Akimel Current condition: Incised, isolated low-flow channels Erosion during higher flows Gravel pits have drained groundwater and degraded habitat

28 Authorized Project Habitat enhancement Terracing / channel re-shaping Grade control structures Bank stabilization Open water / wetlands Cultural and ecological education centers Recreation

29 Authorized Project

30 Restores: Authorized Project 360 hectares cottonwood/willow 150 hectares mesquite 80 hectares wetlands 10 hectares Sonoran desert scrub shrub approximately 8 km of maintained trails $140 M 22 river km

31 Rio Salado Project First ecosystem restoration project for which the Army Corps of Engineers received authorization Challenges included scrutiny by higher authority on high cost of habitat units relative to projects in more hydric communities in the eastern United States Use of potentially-contaminated groundwater for initial irrigation also resulted in scrutiny

32 Rio Salado Project Additional constraints: Regulated Hydrology upstream dams dampen the natural peak flow conditions Poor groundwater quality Need to maintain flood conveyance capacity Source and cost of water Birdstrikes to aircraft a threat Ongoing gravel mining operations

33 Lessons Learned (continued) The challenge in restoration projects is to find creative and defensible solutions Authorization granted by higher Corps authority Groundwater treatment allowed determined to be least cost source of supply Wetland locations for bird refuges moved Agreements reached with mining operators

34 Cost = $100M Length = 10 kilometers 275 hectares restored Restoration Success Demonstration project shown

35 Rio Salado Project

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37 Primary Lesson Learned Partnerships are Critical for Success Flood Control District of Maricopa County US Army Corps of Engineers Gila River Indian Community Salt River Pima- Maricopa Indian Community

38 Questions? Tetra Tech would like to acknowledge and thank the US Army Corps of Engineers, Phoenix office, for making past graphics available