City of Sunset Valley Drainage Master Plan Assessment Final Recommendation Report March 24, 2009

Project Goal Assessment of master drainage plan Development of alternative solutions Develop final recommendations/report Prioritize Drainage Improvements

Review Master Drainage Plan Plan was comprehensive  Identified riverine overtopping of roadways and structural inundation in Old Sunset Valley  Identified 52 localized drainage issues  Identified a mitigation goal of 5-year level of service Cost estimates did not include land acquisition or permitting

Review New Drainage Concepts Recharge features Rooftop harvesting/other Detention pond footprint Upstream detention

Drainage Mitigation Alternatives AlternativeLevel of Service Provided Regional Drainage Plan100 year ultimate development Emergency Access Route100 year ingress/egress Peak Flow Diversion5 year ingress/egress & structure Detention5 year Culvert Improvements5 year ingress/egress Buyout Option 5 Year5 year structure Buyout Option 100 Year100 year structure

Regional Drainage Plan Partnering with City of Austin and Travis County Possible Improvements Include  Modifying West Gate Blvd  Regional Channelization  Regional detention  Regional natural waterway maintenance program

Regional Drainage Plan Advantages  Regional approach will achieve higher level of service  Regional solutions typically generate higher benefit cost ratio Disadvantages  City/County participation unknown Cost (unknown)

Emergency Access Route

Advantages  Provides 100 year ingress/egress  Improves public health and safety  Multi use Disadvantages  Will need to be maintained  Requires 11 easements Cost $ 720,000

Peak Flow Diversion

Advantages  Multi-use improvement  Provides 5 year ingress/egress  Removes 4 homes & 5 structures form 5 year floodplain  Reduces peak flow rates on other storm events Disadvantages  Requires clearing of existing natural area  Not accepted by the public  Easement required (1) Cost $1,600,000

Low Water Crossing Improvements Low water crossing improvements at  Loan Oak Trail  Pillow Road  Reese Drive (not included)  Sunset Trail (not included) Channel Improvements not included Improvements may be incorporated together or individually as funding becomes available

Low Water Crossing Improvements Advantages  Provides 5 year ingress/egress  Improves public health and safety Disadvantages  Does not improve flooding impacts to homes or other structures  Drainage easements may be required on Pillow Road Cost $1,110,000

Buyout Option Purchase homes within the floodplain Median home price $300,000 Cost for demolition and restoration $20,000/lot

Buyout Option 5 Year  Number of homes, 5  Cost $1,280, Year  Number of homes, 30  Cost $9,600,000

Buyout Option Advantages  Removes structures from the floodplain  Provides additional greenbelt areas  Provides land for site/regional detention Disadvantages  Directly impacts several residents  Does not improve ingress/egress

Drainage Programs Reverse 911 Natural Waterway Maintenance Program Funding Options Comprehensive Flood Abatement Program

Final Recommendations Evaluation criteria  Public acceptance30%  Level of service35%  Land Acquisition20%  Cost15% Total100%

Evaluation Matrix

Final Recommendations No. 1, Regional Drainage Plan -(if not feasible then proceed to No. 2) -Cost: Unknown No. 2, Emergency Access Route 100-yr LOS Culvert Improvements 5-year LOS -Cost: $1,830,000 No. 3Emergency Access Route 100-year LOS Flow Diversion 5-year LOS -Cost: $2,370,000

Final Recommendations Programs Development a natural waterway maintenance program If necessary for funding investigate the feasibility of creating a storm water utility Continue the City’s comprehensive flood abatement program Continue to adopt and enforce ordinances that meet or exceed FEMA requirements to reduce the risk of flooding. Educate residents in high and moderate risk flood areas about flood insurance