LONG TERM HYDROLOGICAL IMPACT ASSESSMENT BY L-THIA MODEL

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LONG TERM HYDROLOGICAL IMPACT ASSESSMENT BY
L-THIA MODEL

• Yawar Hussain
• emailyawar.pgn_at_gmail.com

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INTRODUCTION
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OBJECTIVES

• To assess the long term affects of landuse change
  on urban hydrology
• Simulation of runoff and NPS loads
• Use radily available data
• Less expertise requirement
• Generate community awareness

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L-THIA NPS

• L-THIA NPS is an ArcGIS extensoion
• It gives long-term average annual runoff for a
  land use configuration, based on actual long-term
  climate data for that area.
• It is an emprical model.
• By using many years of climate data in the
  analysis, L-THIA focuses on the average impact,
  rather than an extreme year or storm.

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MODEL KEY FEATURES

• Quick, accessible tool to use in assessing the
  long-term impacts of land use change
• Based on computations of daily runoff obtained
  from long term climate records, soil data, curve
  number (CN) value and land use of the area
• Calculates surface runoff averages
• Calculates nonpoint source of pollution (NPS)
• Provides a numeric description of runoff, as well
  as charts and maps for output
• Determines hydrologic impact of land usage

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THEORY
Where, Q is Runoff, P is rainfall, Ia is
Abstraction and S is maximum retention potential
after runoff begin.
(Park et al., 2013)
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SCS-CN

• CN is the indicator of land impermeability
• Uses landuse and soil
• It is coefficent which change the rainfall into
  possible runoff potential
• Remove all the losses like Evaporation,
  Absorption, Transpiration, Surface Storage
• Higher CN higher runoff potential

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FLOW CHART
(Park et al., 2013)
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THE MATRIX TABLE TO PREDICT CHANGE IN LONG-TERM
RUNOFF CONDITIONS

• A matrix of all possible CN changes was prepared
  to simplify sensitivity analysis of alternate
  land use change scenarios
• Any particular cell value at the intersection of
  the pre-development (or land use change) CN (row)
  and the postdevelopment(or land use change) CN
  (column) indicates the percent increase in runoff
  depth (per unit area)

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MATRIX TABLE
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How L-THIA Estimate NPS Pollutant Loadings
using Event Mean Concentration 
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EVENT MEAN CONCETRATION(EMC)
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INPUT DATA PREPARATION

• Degital Elevation Model (DEM)
• Soil Map (Hydrelogical Soil Units )
• A (Sand loam),B (slit loam),C (clay loam)
• Landuse Map
• Rainfall (Correct format)
• Outlet

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SCREEN SHOT
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REFERENCE

• BAIRD, C., JENNINGS, M. (1996).
  CHARACTERIZATION OF NON-POINT SOURCES AND
  LOADINGS TO THE CORPUS CHRISTI BAY NATIONAL
  ESTUARY PROGRAM STUDY AREA. TEXAS NATURAL
  RESOURCE CONSERVATION COMMISSION, TEXAS, 226 PP
• CHOI, W. (2007). ESTIMATING LAND-USE CHANGE
  IMPACTS ON DIRECT RUNOFF AND NON-POINT SOURCE
  POLLUTANT LOADS IN THE RICHLAND CREEK BASIN
  (ILLINOIS, USA) BY APPLYING THE L-THIA MODEL.
  JOURNAL OF SPATIAL HYDROLOGY, 7(1), 114.
• DU, J., HU, S. (2014). THE LONG-TERM
  HYDROLOGICAL IMPACT ASSESSMENT OF LAND USE AND
  LAND COVER CHANGES USING L-THIA MODEL IN THE
  QINHUAI RIVER WATERSHED OF JIANGSU PROVINCE ,
  CHINA. IN ASPRS 2014 ANNUAL CONFERENCE
  LOUISVILLE, KENTUCKY.
• ENGEL, B. 2001. L-THIA NPS LONG-TERM HYDROLOGIC
  IMPACT ASSESSMENT AND NON POINT SOURCE POLLUTANT
  MODEL. U.S. ENVIRONMENTAL PROTECTION AGENCY.

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OBRIGADO