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WinTR-55: Introduction and Background. Objectives: The basics History of WinTR-55 Nuts & bolts of algorithms Demo of model interface. Why model?. To estimate conditions where measurements are not available or possible. To test system understanding. To facilitate design.

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wintr 55 introduction and background
WinTR-55: Introduction and Background
  • Objectives:
        • The basics
        • History of WinTR-55
        • Nuts & bolts of algorithms
        • Demo of model interface
why model
Why model?
  • To estimate conditions where measurements are not available or possible.
  • To test system understanding.
  • To facilitate design.
topology of wintr 55
Topology of WinTR-55
  • Empirical vs. Conceptual
  • Stochastic vs. Deterministic
  • Lumped vs. Distributed
  • Continuous vs. Event-based vs. Peak discharge
history of tr 55
History of TR-55
  • Developed by SCS (now NRCS) for agricultural watersheds in 1954
  • Widely accepted, yet no peer review
  • Adapted for urban watersheds
  • Poor performance in forested watersheds
tr 55 methodology runoff
TR-55 methodology: Runoff
  • Rainfall (P) separated into:
    • Rainfall excess (Q)
    • Initial abstraction (Ia) – interception, infiltration, and depression storage
    • Retention (F) – proportion retained, infiltrated
  • Basic assumption:
  • CN is a function of S, the potential maximum retention
  • → Runoff equation:
tr 55 methodology cn
TR-55 methodology: CN
  • CN range 0-100
    • 0 = no runoff
    • 100 = complete runoff
  • Function of:
    • Hydrologic soil group
    • Cover type
    • Treatment practice
    • Hydrologic condition
    • Impervious area
    • ARC – antecedent runoff condition
  • Can be adjusted for ARCI and ARCIII
tr 55 methodology t c
TR-55 methodology: Tc
  • Time it takes water to travel from most hydrologically distant portion of watershed to the outlet.
  • Many ways to calculate:
    • With limited data:
    • NRCS method:
      • Sheet flow f(length, slope, Manning’s n)
      • Shallow concentrated flow f(length, slope, Manning’s n)
      • Channel flow f(length, slope, Manning’s n, channel dimensions)
  • Other methods incorporate rainfall intensity
tr 55 methodology hydrographs
TR-55 methodology: Hydrographs
  • Unit hydrograph approach:
    • Q = P * unit hydrograph
  • Defined as temporal distribution of runoff resulting from a unit depth (i.e., 1 cm) of rainfall excess occurring over a given duration (i.e., 24 hrs)
  • Default DUH is average shape of a large number of ag watersheds nationwide
  • User-specified DUH can be input
tr 55 methodology routing
TR-55 methodology: Routing
  • Muskingum-Cunge method
  • Most widely used method of stream-channel routing
  • Oj+1 = C1Ij+1 + C2Ij + C3Oj
  • Constants are based on travel time through reach
tr 55 methodology detention
TR-55 methodology: Detention
  • Outlet flow from detention pond:
    • Pipe orifice flow assumed
    • V-notch or rectangular weir
  • All flow routed through structure (no overflow option)
  • Assumes no losses from pond (i.e., infiltration)
tr 55 methodology sub area reach concepts
TR-55 Methodology: Sub-area/Reach Concepts
  • WinTR-55 represents the watershed as a system of sub-areas and reaches.
  • “Sub-areas” are the watersheds that generate hydrographs that feed into the upstream end of a reach.
tr 55 methodology sub area reach concepts1
TR-55 Methodology: Sub-area/Reach Concepts
  • “Reaches” represent the configuration of flow paths within the watershed.
  • Storage routing (Lakes, Structures, Wetlands, etc.) and Channel Routing take place within a Reach.
  • All WinTR-55 modeled watersheds end with the final stream reach terminating at an “Outlet”
schematic example
Schematic Example

Sub-area 2

Reach 2

Outlet

(ChannelRouting)

Sub-area 3

Reach 1

(StorageRouting)

Legend

Sub-area 1

Storage Area

Sub-Area Inflow Points

other tr 55 criteria
Maximum Area

Number of Sub-areas

Tc for any sub-area

Number of reaches

Types of reaches

Rainfall Depth

Rainfall Distributions

Rainfall Duration

Antecedent Runoff Condition

25 square miles

1-10

0.1 hour < Tc < 10 hours

0-10

Channel or Structure

0-50 inches (0-1,270mm)

NRCS Type I, IA, II, III, NM60, NM65, NM70, NM75, or user-defined

24-hour

II (average)

Other TR-55 Criteria
application of tr 55
Application of TR-55
  • Raingarden design for Votey parking lot runoff
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