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

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

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 out 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 - Ecologi Ec gica cal May introduce invasive species to pool (zebra mussels, others) 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 osal 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 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