translating soils information for hydrological modelling reflecting on the big picture from the...
TRANSCRIPT
Translating Soils Information
for Hydrological Modelling Reflecting on the Big Picture from the 1970s
to the Present
Roland Schulze Professor Emeritus of Hydrology & Senior Research Associate
Centre for Water Resources Research School of Agricultural, Earth & Environmental Sciences
University of KwaZulu-Natal, Pietermaritzburg, RSA
Defining Moments …From Way Back !
1. “A vital role is played by soil, for it is the capacity of the soil to absorb, retain and release water that is the prime regulator of the evapotranspiration and runoff response of a catchment” (England & Stephenson, 1970)
2. A catchment is not a lumped system in regard to soils, and pronounced differences in magnitude and sequence of hydrological processes have been observed in soil units within a catchment (England, 1970)
3. “Soils of the Tugela Basin” (van der Eyk et al., 1969)
Falling in Love …With a Subject MatterDefining Years …1970 -1974
The Drakensberg
Cathedral Peak Research Catchments
Energy and Water Budgets on Slopes with Different Gradients & Aspects
‘TOP’ OF THE ATMOSPHERE
EXTRATERRESTRIAL RADIATION
Solar Constant (1361 W.m-2)
Earth’s Radius Vector (Time of Year)
Angle of Inclination
(Latitude; Time of Year; Time of Day)
Direct Radiation ATTENUATIONS
Atmosphere (Water Vapour; Aerosols; Altitude; Optical Air mass)
Terrain (Slope; Aspect; Albedo)
Cloud (Type; Time of Day)
N
E
S
W ASPE
DALT Normal to Slope N
S
AZIM
ALT
W
N
S
E
SLP
THET
Diffuse Radiation ATTENUATIONS
Solar Altitude
Slope
(b) HORIZON SHADING ALT < HOR
(a) SLOPE SHADING ALT < SLP
ALT
HOR
ALT
SLP
1000 -
750 -
500 -
250 -
0 - 17 16 15 14 13 12 11 10 9 8 7
Time of Day (h)
Glo
bal
Rad
iati
on
Flu
xes
(W.m
-2)
- - - 35o NNW (290o)
32o S (170o)
NOVEMBER 20, 1986
Mapping Energy
Budgets on Sloping Terrain
Considerations
Verification
Land Cover Class Land Treatment/Practice/Description
Stormflow Potential
Hydrological Soil Group A A/B B B/C C C/D D
Veld (range) and Pasture
1 = Veld/pasture in poor condition 2 = Veld/pasture in fair condition 3 = Veld/pasture in good condition 4 = Pasture planted on contour 5 = Pasture planted on contour 6 = Pasture planted on contour
High Moderate Low High Moderate Low
68 49 39 47 25 6
74 61 51 57 46 14
79 69 61 67 59 35
83 75 68 75 67 59
86 79 74 81 75 70
88 82 78 85 80 75
89 84 80 88 83 79
Irrigated Pasture Low 35 41 48 57 65 68 70 Meadow Low 30 45 58 65 71 75 81 Woods and Scrub
1 = Woods 2 = Woods 3 = Woods 4 = Brush - Winter rainfall region
45 36 25 28
56 49 47 36
66 60 55 44
72 68 64 53
77 73 70 60
77 73 70 60
83 79 77 66
Orchards 1 = Winter rainfall region, understory of crop cover 39 44 53 61 66 69 71
Forests & Plantations
1 = Humus depth 25mm; Compactness: 2 = " " " 3 = " " " 4 = Humus depth 50mm; Compactness: 5 = " " " 6 = " " " 7 = Humus depth 100mm; Compactness: 8 = " " " 9 = " " " 10 = Humus depth 150mm; Compactness: 11 = " " " 12 = " "
compact moderate friable compact moderate friable compact moderate friable compact moderate friable
52 48 37 48 42 32 41 34 23 37 30 18
62 58 49 58 54 45 53 47 37 49 43 33
72 68 60 68 65 57 64 59 50 60 56 47
77 73 66 73 70 62 69 64 56 66 61 52
82 78 71 78 75 67 74 69 61 71 66 57
85 82 74 82 78 71 77 72 64 74 69 61
87 85 77 85 81 74 80 75 67 77 72 65
Urban / Sub-Urban Land Uses
1 = Open spaces, parks, cemeteries 75% grass cover 2 = Open spaces, parks, cemeteries 75% grass cover 3 = Commercial/business areas 85% grass cover 4 = Industrial districts 72% impervious 5 = Residential: lot size 500m2 65% impervious 6 = " " 1000m2 38% impervious 7 = " " 1350m2 30% impervious 8 = " " 2000m2 25% impervious 9 = " " 4000m2 20% impervious 10 = Paved parking lots, roofs, etc. 11 = Streets/roads: tarred, with storm sewers, curbs 12 = " gravel 13 = " dirt 14 = " dirt-hard surface
39 49 89 81 77 61 57 54 51 98 98 76 72 74
51 61 91 85 81 69 65 63 61 98 98 81 77 79
61 69 92 88 85 75 72 70 68 98 98 85 82 84
68 75 93 90 88 80 77 76 75 98 98 88 85 88
74 79 94 91 90 83 81 80 78 98 98 89 87 90
78 82 95 92 91 85 84 83 82 98 98 90 88 91
80 84 95 93 92 87 86 85 84 98 98 91 89 92
1979 SCS Manual Effects of SCS Soil Groups on Curve Numbers
0
2
4
6
8
10
0
10
20
A/B B/C D
Pe
ak
Dis
cha
rge
(m
3 /s)
Sto
rmfl
ow
(m
m)
SCS Soil Group
Sensitivity of Hydrological Responsesto SCS Soil Groups
How Sensitive are Stormflow Volume & Peak Discharge to SCS Soil Groups?
Example
Catchment Area = 2 km² Precipitation = 50 mm Land Cover = Veld in fair condition Catchment Slope = 8 % Length of main Stream = 1 500 m
Conclusion Highly sensitive
Meanwhile, on the Soil Science Front … The “Red Book”: MacVicar et al. 1977
Soil Classification – A Binomial System for South Africa01
02
A1A2 or
E
A3
B1
B2
B3
O
A
B
C
R
G(Gley)
Loose leaves and or-ganic debris, largelyundecomposed
Organic debris, partial-ly decomposed ormatted
Dark coloured due to ad-mixture of humified or-ganic matter with themineral fraction
Maximum expression ofB horizon character
Transitional to C
Unconsolidatedmaterial
Hard rock
Light coloured mineralhorizon
Transition to B butmore like A than B
Transition to A butmore like B than A
Master Horizons
(MacVicar et al., 1977)
O
A1
E
B2
G
C
Organic
HumicVerticMelanicOrthic
PedocutanicPrismacutanicGleycutanicLithocutanic
NeocutanicFerrihumic
Hard plinthicSoft plinthicYellow-brown
apedalRed apedalRed structured
Diagnostic Horizons (SCWG, 1991)
QUICKFLOW
RUNOFF
INTERCEPTION
PRECIPITATION
GROUNDWATER STORE
INTERMEDIATE STORE
SUBSOIL
TOPSOIL
SURFACE LAYER
Early 1980s The beginnings of ACRU A physical-conceptual, process based,
daily time step water budget model
?
QIOBSTQ?
IOBSPK?PEAK
QFRESP
IRUNQ
P
ADJIMP
COIAM
SMDDEP
COFRU
P = Precipitation (mm)Ia = Initial abstractions (mm)
= f (S)S = Soil water deficit (mm)
Q = (P – Ia)2 / (P – Ia + S)
The ACRU Approach
With that, in the mid-1980s, the need to classify soils in South Africa hydrologically
Working with Cass, Hutson et al
Clay Distribution
Type
ɵ at PWP ɵ at DUL
Topsoil
Subsoil
Topsoil
Subsoil 1a 1b 1c 1d 1e 2a 2b 2c 2d 2e 3a 3b 3c 3e 3h 3k 5a 5b 5c 5d
0.064 0.083 0.112 0.173 0.231 0.067 0.089 0.138 0.202 0.250 0.067 0.067 0.067 0.089 0.138 0.202 0.067 0.089 0.138 0.202
0.065 0.091 0.158 0.226 0.265 0.062 0.084 0.133 0.197 0.245 0.084 0.110 0.142 0.133 0.181 0.245 0.057 0.068 0.092 0.124
0.158 0.180 0.213 0.282 0.348 0.162 0.187 0.242 0.315 0.370 0.162 0.162 0.162 0.187 0.242 0.315 0.162 0.187 0.242 0.315
0.171 0.201 0.277 0.354 0.398 0.168 0.193 0.248 0.321 0.376 0.193 0.222 0.259 0.248 0.303 0.376 0.158 0.175 0.202 0.239
Vertical Clay
Distribution Model/Class
θ at Permanent Wilting Point (m3/m3)
θ at Drained Upper Limit (m3/m3)
Topsoil
θPWPA Subsoil
θPWPB Topsoil
θDULA Subsoil
θDULB 1a b c d e 2a b c d e 3a b c e h k 5a b c d
.064 .083 .112(.127) .173(.226) .231(.320) .067 .089 .138(.169) .202(.273) .250(.352) .067 .067(.054) .067(.054) .089(.091) .138(.169) .202(.273) .067 .089 .138 .202
.065 .091 .158(.211) .226(.320) .265(.383) .062 .084 .133(.169) .197(.273) .245(.352) .084 .110(.132) .142(.185) .133(.169) .181(.247) .245(.352) .057 .068 .092 .124
.158 .180 .213 .282 .348 .162 .187 .242 .315 .370 .162 .162 .162 .187 .242 .315 .162 .187 .242 .315
.171 .201 .277 .354 .398 .168 .193 .248 .321 .376 .193 .222 .259 .248 .303 .376 .156 .175 .202 .239
Soils Issues for Hydrologists
And, the Advent of Soils LAND TYPES from the Binomial Soil Classification, and their Databases
# Based on relatively uniform climate, terrain, soil patterns # With detailed soils inventory on soil series, clay %, texture class, profile thickness… # With the Land Type made up of several soil series# Including information on Terrain Units making up a Land Type
“Translating” Land Type Information to Hydrological Model Needs
Rules for Partitioning Soil Horizon Thicknesses
Drilling Down to Terrain Unit Level
BASIC PREMISE
Operational hydrological models should be able to be “driven” by standard datasets which are freely available from national networks and by standard (usually non-hydrological) spatial digital information available at national level, suitably “translated” (I.e. converted) into model input variables, for the models then to operate over a range of desired spatial scales
Result … Detailed mapping of soil attributes which are critical to hydrological modelling from 16600+ Land Type Polygons
(Schulze and Horan, 2008)
Result … Detailed mapping of soil attributes which are critical to hydrological
modelling (Schulze and Horan, 2008)
Result … Detailed mapping of soil attributes which are critical to hydrological modelling (Schulze and Horan, 2008; Schulze,
2012)
Quo vadis? An operational hydrologist’s perspective
Operationalising terrain unit delineation Mapping soil fertility in detail Getting a better handle on hydraulic conductivity Towards a general model of interflow Ringfencing soils with high organic matter content More detailed delineation of wetlands soils Delineating unstable soils for hydrological
modelling Getting a better handle on drainage rates of soils