Frequency Surface Response: Supporting Flash Flood Decision Making

1
Frequency Surface Response Supporting Flash
Flood Decision Making
2
Program goals

• Enhance Flash Flood support with a true
  hydrologic/hydraulic model simulation.
• Offer QPF driven insight into a basins potential
  response given current basin states.
• Couple WFO regional expertise and RFC modeling
  to best serve the local hydrologic needs of the
  community.

3
Concept

• Utilize the Hydrologic-Lab Research Distributed
  Hydrologic Model (HL-RDHM) to provide
  connectivity and past event/soil state carryover.
• Compare each cells discharge (channel flow) and
  surface flow (non-channelized flow) to historic
  distribution of hourly values. Returns the
  percentile.
• Display these values in near real-time via the
  CBRFC web page.
• Over time, work with the WFO to identify the
  threshold percentiles at which impacts to lives
  and property occur.

4
Concept Contd
For Each Cell
Critical Threshold
Frequency
Discharge
Grid of Discharge
Discharge Exceedence values
5
Basin HL-RDHM Model Structure
Snow Pack
Water content in Soil tanks, ET
Snow17
Rain melt
FRZ (Sac-HT)
SAC-SMA
Surface and subsurface flow
Runoff
Water Contents at Depth
Kinematic Wave Routing
surfaceFlow Discharge Hydrograph
6
HL-RDHM Model Hydraulic Methods Channel and
Hill-slope routing (Discharge)
Real HRAP Cell
Hillslope model
Cell-to-cell channel routing
From Yu Zhang, 2006
7
Why two separate parameters to address cell
response?

• Surface Flow excess, unrouted water (mm/sec),
  from the HRAP cell. Does this provide information
  not included in the Channelized flow?
• Discharge local cell flow plus the upstream
  flows

8
Frequency Discharge Example
Discharge Percentile
Discharge
9
Threshold Frequency Discharge Grids
Animation Open the below file with Firefox.
file//ss1/epc/gorms/images/Threshold_flow/TFQ_ani
mation/tfq_anim_2.png
10
Frequency Surface Flow Example
11
Threshold Frequency SurfaceFlow Grids
Animation Open the below file with firefox.
File/ss1/epc/gorms/images/Threshold_flow/TFsF_ani
mation/tf_sf_animation.png
12
(No Transcript)
13
Improvements

• Incorporates soil, land use, slope and vegetation
  cover into a calibrated model.
• Adds connectivity to route multiple headwater
  basin cells into downstream cells.
• Remembers the carryover in soil moisture states
  from previous events.
• Values are relative to previous response. WFOs
  can develop knowledge of their local regional
  problem areas.

14
Cell value time series -- Are Hydrologic
Conditions getting better or worse?
15
Meeting WFO needs

• Dissemination methods Stand alone viewer,
  incorporate within other gridded data products,
  etc?
• QPF Could we incorporate meaningful WFO
  generate QPF into such a system, and how?
• Ground Truth Impact How do we determine the
  threshold at individual known problem cells?