Transcript Configuring the ACRU Modelling System

Configuring the ACRU model
Andy Pike
School of Bioresources
Engineering and Environmental
Hydrology.
University of Natal,
Pietermaritzburg.
STEP 1: Define the Problem
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The configuration will be determined by the
problem at hand
Try and foresee the questions that might be
asked in the future to pre-empt a further
configuration at a later stage
STEP 2: Fieldwork
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Fieldwork is essential to account for changes
in land cover and catchment development
which are not reflected in the traditional
information sources
Field visits can often give the modeller an
idea of the hydrological responses of the
various subcatchments
STEP 3: Delimit the
Subcatchments (1 of 4)
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Catchment boundaries should be natural
watersheds and should account for the
following features:
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Special points of interest
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Abstraction points, effluent/irrigation return flows, point
sources of pollution, water treatment plants, IFR sites
STEP 3: Delimit the
Subcatchments (2 of 4)
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Soils
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Exposed rock, highly eroded areas, water repellant soils
(hydrophobic soils), geology
Land cover
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Wetlands, commercial and indigenous forests, land
cover in pristine condition
Agricultural areas
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irrigated and dryland cultivation, intensive/commercial
agriculture, subsistence agriculture
STEP 3: Delimit the
Subcatchments (3 of 4)
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Rainfall
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Topography
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Catchments can be divided when a large variation in
Mean Annual Precipitation is evident
slope
altitude
Impoundments
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Major dams should always be at the outlet of a
subcatchment
STEP 3: Delimit the
Subcatchments (4 of 4)
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Gauging stations and weirs
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These need to be at the outlet of subcatchments in order
for the simulated streamflows to be compared to
observed data
STEP 4: Digitise and Number (1 of 3)
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The subcatchment boundaries need to be
digitised accurately and the areas need to be
determined in km2
Each subcatchment should be numbered in
sequential order from the sources to the
mouth
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These numbers should be entered as a new field
in the attribute table of the Shapefile
STEP 4: Digitise and Number (2 of 3)
(from page AT2-13 of the ACRU Theory Manual)
STEP 4: Digitise and Number (3 of 3)
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A utility (CreateMenuFromGIS) is available
from the School of Bioresources Engineering
and Environmental Hydrology to assist the
users in configuration of catchments from
ArcView
(see http://www.beeh.unp.ac.za/pike/fortran/fortran_main.htm)
STEP 5: Rainfall
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Selection of appropriate “Driver” rainfall stations
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Identify all rainfall stations in the immediate area
Select the most appropriate “driver” station for each subcatchment (based
on years of record, MAP, altitude, distance away from the subcatchment)
Infil missing records and make sure that they form concurrent periods
Check for problems of “phasing”
Calculate adjustment factors from catchment and station median monthly
rainfall in order that the point rainfall data are more representative of the
catchment’s rainfall
A utility (CALC_PPTCOR) is available from the School of Bioresources
Engineering and Environmental Hydrology to assist the users in this
process
(see http://www.beeh.unp.ac.za/pike/fortran/fortran_main.htm)
STEP 6: Other Climate Information
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Mean monthly A-pan data
Median monthly maximum and minimum
temperatures
Daily maximum and minimum temperature
data
STEP 7: Soils Information
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Sources:
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ISCW Land Type Database
SIRI 84 Homogeneous Soil Zones
ARC Biotopes
A utility (AutoSoils) which automatically assigns
soil water retention and drainage characteristics
to each ISCW Land Type is available from the
School of Bioresources Engineering and
Environmental Hydrology
STEP 8: Landuse Information
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Sources:
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Acocks’ Veld Types (follow “Tips and Tricks” link from
http://www.beeh.unp.ac.za/acru/)
CSIR (Environmentek) National Land Cover (NLC)
Database (click icons below)
NLC1994/1995
NLC2000
STEP 9: Streamflow/Runoff
Information
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The following variables and parameters control the
generation and timing streamflow:
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stormflow response fraction for the catchment/subcatchment
(QFRESP)
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coefficient of baseflow response (COFRU)
effective (critical) depth of the soil (m) from which stormflow
generation takes place (SMDDEP)
option to include or exclude baseflow from the simulation of
streamflow (IRUN)
fraction of the catchment occupied by adjunct impervious areas
(ADJIMP)
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fraction of the catchment occupied by impervious areas which
are not adjacent to a watercourse (DISIMP)
surface storage capacity (i.e. depression storage, or initial
abstraction) of impervious surface (STOIMP)
option to simulate the water budget of an internally drained area
(LYSIM)
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coefficient of initial abstraction (COIAM)
STEP 10: Irrigation Information
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Requirements:
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Areas irrigated
Months during which irrigation occurs
Application rates and modes of scheduling
(amounts and cycles)
Crop irrigated and their growth characteristics
STEP 11: Abstractions
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Volumes and timing
Source (run-of-river or impoundment)
Return flows
STEP 12: Impoundments
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Surface area
Volume
“Internal” (farm dams) or “external”
Environmental flow releases, legal flows and
seepage
Evaporation
STEP 13: Verifications
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Comparison of simulated flows to observed
data (daily, monthly or annual)
Use:
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Regression and comparative statistics
Time series plots
1:1 plots
Double mass plots
STEP 14: Scenarios
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Evaluate the impacts of changes in:
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land cover
land use and management
operating rules
optimisation of irrigation scheduling
optimisation of dam sizing
Consult the ACRU Homepage for
further information
http://www.beeh.unp.ac.za/acru