Hydrologic Modeling with SSARR and HEC-HMS

1. Hydrologic Modeling with SSARR and HEC-HMS Crane Johnson, PE Hydraulic Engineer US Army Corps of Engineers Alaska District

2. SSARR • Streamflow Synthesis and Reservoir Regulation Model • Streamflow Synthesis and Reservoir Regulation (SSARR) Model was developed to provide mathematical hydrologic simulations for systems analysis as required for the planning, design, and operation of water control works. • Consists of two Sub-models: • Watershed Model • River System and Regulation Model

3. SSARR • Developed in the 1960’s by the Corp of Engineers Northwest Division, last major update 1991 • Still used today to model un-regulated Columbia and Snake River flows • Written in FORTRAN 77, DOS Operating System • Used by the Alaska District as an Operational model to forecast flood flows for the Chena River Lakes Project.

4. FAIRBANKS FLOOD OF 1967 • 6.20” of rain in Fairbanks (August 1967) • 74,000 cfs, Downtown Fairbanks Photo courtesy of VF Addendum, 89-12-83, Archives, University of Alaska Fairbanks. • Displaced 7,000 People • $80 Million in Damages • Inspired Congress to pass the National Flood Insurance Program (NFIP)

5. Chena River Lakes Project 1958 – Project Authorized 1968 – Project Re-Authorized 1970 – Design Begins 1973 – Tanana Levee Construction Begins 1975 – Moose Creek Dam Construction Begins 1979 – Moose Creek Dam Operational 1981 – Project Test Fill 1988 – Construction of All Project Elements Complete

6. CHENA RIVER LAKES PROJECT OPERATIONAL SCHEMATIC

7. ALASKA DISTRICT DAM SPECIFICATIONS • TYPE: Zoned Earth Fill • ELEVATION: 528.7 Feet MSL (max @ top) • HEIGHT ABOVE STREAM BED: 50 feet • LENGTH: 40,200 feet • WIDTH AT TOP: 24 feet • VOLUME OF FILL: 6,231,000 cubic yards • STORAGE CAPACITY: 224,000 acre-feet • @ 525 feet elevation @ control works

8. ALASKA DISTRICT DISCHARGE FACILITY Type: Concrete gravity control works Gates: 4 steel, vertical lift Gate Openings: 18 ft high X 25 ft wide Fishways: 2 each, 5 ft wide X 18 ft high Fish Ladder: Vertical slot width = 0.75 feet Maximum discharge = 26 cfs

9. CHENA FLOODWAY • Length: 27,000 ft (Chena River to Highway Bridges) • Minimum Width of cleared flow channel: 1,100 feet • Maximum Width of cleared flow channel: 4,200 feet • Channel-peak design outflow: 160,000 cubic feet per second • Floodway Sill: • Type: Sharp-Crested Weir • Material: Sheet piling with • rolled concrete stilling basin • Crest Elevation: 506.65 feet (MSL) • Crest Length: 2,000 feet • Purpose: Prevent Tanana River floods • from entering Chena River.

10. ALASKA DISTRICT HIGH WATER EVENTS • 20 High Water Events from 1981 through 2008 • The 3 Largest Events to Date: • Peak Peak Peak Gate • Floodway Flow @ Flow @ Closure • Elevation Outlet Works Fairbanks Duration • Dates Feet (MSL) (CFS) (CFS) (DAYS) • May-June 1992 507.6 8,200 10,500 18 • May 1991 503.0 8,300 11,350 11 • May-June 1985 505.3 8,250 8,950 12

11. ALASKA DISTRICT CHENA RIVER LAKES FLOOD CONTROL PROJECT

12. ALASKA DISTRICT CHENA RIVER LAKES FLOOD CONTROL PROJECT • Chena River Lakes Project SSARR Model • Lumped parameter model with 4 sub-basins • Each sub-basin includes elevation bands • Moose Creek Dam and Reservoir Included • Two sets of operating rules • Maximum release • Minimum release (upstream fish migration)

13. ALASKA DISTRICT CHENA BASIN SSARR MODEL Watershed Sub-Model Basin weighted averages (with elevation zone adjustments) for: Air Temp Precipitation Interception – Bucket Model Evapotranspiration – Thornwaite Method (adjusted for elevation, season and snowcover) Snowmelt – Temperature Index Method Runoff – Empirical relationship SMI vs. Runoff% (varies with rainfall rate) Four runoff zones are routed to the Stream (routing through series of small lakes)

14. ALASKA DISTRICT CHENA BASIN SSARR MODEL • River System and Regulation Sub-Model • Reservoir Routing – Continuity of storage equation • Stream Routing – Cascade of reservoirs • Time of Storage decreases with increasing Q KTS Ts= Qn

15. ALASKA DISTRICT CHENA BASIN SSARR MODEL

16. ALASKA DISTRICT CHENA BASIN SSARR MODEL • Strengths: • Includes both watershed and river routing processes • Includes reservoirs and regulation operating rules • Long history of use in Interior Alaska • Empirically based methods with lots of calibration data • Weaknesses: • Difficult user interface • Limited graphical output capabilities • Empirically based model – limited hydrologic methods available • No automatic adjustment of initial conditions available

17. HEC-HMS Hydrologic Engineering Center - Hydrologic Modeling System (formerly HEC-1) • HEC “NexGen” Project Begins 1990 • (RAS, HMS, FDA) • First HEC-HMS Release April 1998 • Version 1.1 Released April 1999 • Current Version 3.4

18. ALASKA DISTRICT HEC-HMS HEC-1 HEC-HMS Purpose of HEC-HMS • Improved User Interface, Graphics, and Reporting • Improved Hydrologic Computations • Integration of Related Hydrologic Capabilities Importance of HEC-HMS • Foundation for Future Hydrologic Software • Replacement for HEC-1 (Advanced Version)

19. ALASKA DISTRICT HEC-HMS IMPROVEMENTS OVER HEC-1 • Ease of use • Projects divided into three components • User can run projects with different parameters instead of creating new projects • Hydrologic data stored as DSS files • Capable of handling NEXRAD-rainfall data and gridded precipitation • Quasi-distributed model

20. ALASKA DISTRICT HEC-HMS • 3 Major Hydrologic • Processes for each Basin • Losses (10 methods) • Transformation to runoff (7 methods) • Transformation to baseflow (5 methods)

21. ALASKA DISTRICT HEC-HMS Six Streamflow Routing Methods • Hydraulic Methods • Kinematic Wave Method • Muskingum-Cunge Method • Hydrologic Methods • Muskingum Method • Storage Method (Modified Puls) • Lag Method

22. ALASKA DISTRICT EKLUTNA HEC-HMS MODEL

23. ALASKA DISTRICT CHENA RIVER LAKES PROJECT Advantages SSARR HEC-HMS

24. ALASKA DISTRICT QUESTIONS????