BART BA RTON SP SPRI RING NGS P POOL OOL: Upper Da Dam M - - PowerPoint PPT Presentation

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BA BART RTON SP SPRI RING NGS P POOL OOL: Upper Da Dam M Modi difi fica cati tion

• ns

s - Gate tes a s and G d Grav avel C Catch tcher

David Johns, P.G., Program Manager/Geologist, Watershed Protection Joint Parks Board and Environmental Commission May 29, 2018

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Backg ckgrou

• und
• 4 portals (openings) in

upstream dam

• Closed in 1970’s during

bypass construction due to increasing poor water quality in creek following storm events

• Creek flows greater than 500

cfs floods BSP

• Gravel catcher in creek 200 ft

upstream of BSP

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Pr Propos

• sal

al

Re-open one or more portals in upstream dam Add gates to portals to regulate timing and volume of creek flow entering pool Remove upstream “gravel” catcher

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Reasoning ning

Barton Springs Pool is hydraulically and ecologically isolated from it’s surface watershed except during floods and pool drawdowns BSP Master Plan – flow regime improvements Significant upstream creek flow 25-30% of time (1998- 2017)

• Longest 213 days (mid-October to mid-May)
• About 20 long flow events in swim season
• 9 flow events greater than 90 days

Gravel catcher doesn’t capture gravel and is causing erosion on north bank of the creek

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Portal tal Ad Advantag tages s – Water Q er Qualit lity

Creates more natural flow regime in pool (BSP Master Plan, Habitat

Conservation Plan)

Creek flow into pool can aid post- flood cleaning by helping transport sediment and debris

• ut of pool

Inflow of creek water will allow faster turn over in pool following storm events

• Creek water quality improves quicker

than springs

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Portal tal Di Disadv sadvan anta tage ges s – Water er Qualit lity

Another detail to attend to at the pool, especially during flood preparation Open gates may create fast currents in upper area of shallow end of the pool Gates could be damaged during flood event and not close

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Portal tal Ad Advantag tages s - Ec Ecologi gical al

Improves connection of pool with creek

• Plants
• Fishes
• Other organisms including salamanders

May improve salamander prey May reduce fine sediment deposition in some habitat areas May reduce salamander stranding as pool is drawn down

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Portal tal Di Disadv sadvan anta tage ges s - Ec Ecologi gica cal

May introduce invasive species to pool (zebra mussels,

• thers)

May introduce more fish predators for salamanders Creek current could encourage nuisance algae growth in current in shallow end

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Gravel C el Catche her

Doesn’t capture gravel Mainly used as a creek crossing Removal previously proposed in 2014-15 Removal opposed by some citizens in Barton Hills

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Grav avel C Catch tcher Pr Propos

• sal

al

Remove structure Repair and restore eroding creek bank

C I T Y Y O F A U A U S T I N I N W WAT E R S H S H E D P D P R O T E C T C T I O I O N D E PA R A R T M E N T

Gravel C el Catche her

Advantages

• Removes unnecessary infrastructure
• Repair and restore creek bank

Disadvantages

• Removes commonly used path across creek