Wintr 55 introduction and background
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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

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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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