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# WinTR-55: Introduction and Background - PowerPoint PPT Presentation

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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Presentation Transcript
WinTR-55: Introduction and Background

• Objectives:

• The basics

• History of WinTR-55

• Nuts & bolts of algorithms

• Demo of model interface

• To estimate conditions where measurements are not available or possible.

• To test system understanding.

• To facilitate design.

• Empirical vs. Conceptual

• Stochastic vs. Deterministic

• Lumped vs. Distributed

• Continuous vs. Event-based vs. Peak discharge

• Developed by SCS (now NRCS) for agricultural watersheds in 1954

• Widely accepted, yet no peer review

• Poor performance in forested watersheds

• 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:

• 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

• 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

• 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

• 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

• 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

• 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 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”

Sub-area 2

Reach 2

Outlet

(ChannelRouting)

Sub-area 3

Reach 1

(StorageRouting)

Legend

Sub-area 1

Storage Area

Sub-Area Inflow Points

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

• Raingarden design for Votey parking lot runoff