Presented by Birhanu Zemadim (IWMI) and Emily Schmidt (IFPRI) at the Nile Basin Development Challenge (NBDC) Science Workshop, Addis Ababa, Ethiopia, 9–10 July 2013

1. 1
Understanding impacts of sustainable land
management interventions using SWAT
Hydrological Model
Birhanu Zemadim (IWMI)
and
Emily Schmidt (IFPRI)
Nile Basin Development Challenge (NBDC) Science Workshop
Addis Ababa, Ethiopia, 9 – 10 July 2013

2. • Brief overview of previous research on
Sustainable Land and Watershed
Management (SLWM)
• Landscape level investments in SLWM
• Hydrological simulations of watershed
investments
• Implications of SLWM
• Conclusions and Upcoming Research
Outline of presentation

3. Overview of previous research
– Chemoga watershed (Blue Nile basin): cropland expansion and
overgrazing attributed to significant declines in dry season
stream flow from 1960-1999. (Bewket and Sterk, 2005)
– May ZegZeg catchment (north Ethiopia): stone bunds, check
dams and abandonment of post-harvest grazing permitted
farmers to plant crops in previously active gullies – increased
infiltration and decreased runoff volume (Nyssen, 2010)
– On-farm experimental sites in diverse agro-ecological zones:
SLWM investments reduced soil loss and runoff in semi-arid
watersheds; however increases in agricultural yields did not
outweigh the estimated costs of soil conservation. (Herweg and
Ludi, 1999)

4. Cntd.. Overview of previous research
• Soil loss due to erosion vary by location, which reflects
the varying Ethiopian landscape and soil characteristics
– Highlands test plots on cultivated land: 130 to 170 metric tons
ha / year on cultivated land. (Hurni, 2008)
– Medego watershed, North Ethiopia: 9.63 metric tons ha/year
(Tripathi & Raghuwanshi, 2003).
– Chemoga watershed in the Blue Nile Basin: 93 metric tons
ha/year (Bewket & Teferi, 2009).
– Borena woreda, South Wollo: ranged from 0 loss in the flat
plain areas to over 154 metric tons ha/year in some areas.
(Shiferaw, 2011)

5. Study Sites: in the Blue Nile Basin of Ethiopia
Dapo watershed 18 km2
Mizewa watershed 27 km2
Meja watershed 96 km2

6. Simulation of watershed landscape-level investments
Slope gradient Share
Under 5 0.13
5-20 0.65
>20 0.22

7. Root Zone
Vadose
(unsaturated)
Zone
Shallow
Aquifer
Confining Layer
Deep Aquifer
Evaporation and
Transpiration

8. Location of Watershed Outlet

9. Watershed Flooding

10. Watershed drought
Photo taken in March 2013

11. Households Using Sustainable Land
Management (SLM) on Private Land
District
Percent of
district
Year of first
Community
Program
Most common
activity on private
land (percent)
Alefa 50% 1990 soil bund (64.2)
Fogera 54% 1983 stone terrace (65.8)
Misrak Estie 54% 1977 stone terrace (36.1)
Gozamin 21% 1988 soil bund (40.9)
Dega Damot 82% 1986 soil bund (42.8)
Mene Sibu 7% 1992 soil bund (89.8)
Diga 32% 2000 irrigation canal (2.9)
Jeldu 2% na stone terrace (24.0)
Toko Kutaye 79% 1989 soil bund (33.7)

12. SLWM Investments
Soil Bunds Wood check dam
Stone terraces Stone check dam

13. Perceived Most Successful SLWM activities
(% of households)

14. Simulation of landscape-level investments
• Investment decisions are simulated to take into
account tradeoffs in labor and land investment and
terrain type:
1. Terracing on steep hillsides
2. Terracing on mid-range and steep hillsides
3. Terracing on mid-range and steep slopes with
bund construction on flatter areas
4. Residue management on all agricultural terrain
(.5 – 1 tons/ha of residue left on field).
5. Mixed strategy of terraces in steep areas and
residue management on mid-range terrain
Labor
Land

15. a) Newly constructed
Fanya Juu terrace /bund
b) Fanya Juu after five
years of construction
Source: IWMI Africa Rainwater harvesting diagram
Terraces and bunds to slow runoff, increase
percolation and decrease erosion

16. Residue Management to stabilize soil, trap
sediment, decrease runoff
• Crop residues are important to stabilize soil, as well as
replenish soil nutrients
– Restricted grazing on agricultural and pasture land
– Minimum tillage on agricultural land
• Current practices (Terefe, 2011 – Chorie, North Wollo)
– Crop residue used for:
• Stall feeding and stubble grazing (74-90%),
• Fuel (11-15%),
• Sale during extended dry season
– Livestock graze on stubble in field until planting the following
season (in some areas considered communal grazing)

17. Model setup and calibration
• August of 2011 – December 2012 (and ongoing)
– Network of data gages installed and collecting daily data
• Soil moisture probes
• Automatic and manual stream level gauges
• Automatic and manual weather stations and rain gauges
• Shallow ground water monitoring devices
– Calibrate surface, groundwater and total runoff: Observed
versus simulated
– Calibrating the SWAT model requires adjusting a number of
sensitive parameter values and their combinations, which in
turn determine runoff behavior.
– Model was calibrated at a daily, weekly and monthly time step

18. Calibration: observed and simulated stream flow
Calibration Validation
ENS R2 ENS R2
Weekly .72 .73 .61 .69
Monthly .93 .94 .71 .81

19. Model simulation
• Assume future weather patterns will display similar trends to
previous years, simulations utilizing Bahr Dar rainfall and weather
data from 1990 – 2012.
• July and August experience the greatest rainfall and runoff
volumes, and minimum runoff volumes occur between March and
April

20. Average Annual Flow and Sediment yield (1990-2012)
Base
(mm)
Terrace
(>20°)
Terrace
(>5°)
Terrace
and
bund
Residue
mgt. (all)
Residue
mgt. and
terrace
Surface flow 45.0 -15% -45% -50% -17% -26%
Lateral flow 200.3 1% 3% 3% 1% 2%
Groundwater
flow
72.2 0% 13% 15% 6% 5%
Stream flow 317.6 -1% -2% -2% -0.5% -1%
Sediment
(erosion)
1.99 -45% -83% -85% -19% -54%
• Constructing terraces and bunds on different slope gradients provides the
largest reduction in surface runoff and erosion. Increases groundwater flow by
15 %. However this intervention is very labor intensive (and pests may be an
issue).
• Terracing on only steep agricultural slopes (>20%) decreases surface flow by 15%
and erosion by 45%.
• Residue management at mid-range slope paired with terraces on steep slopes

21. Average Monthly Surface Flow (1990 – 2012)
• Terracing on steep slopes similar to residue mgt. on all agricultural land
• Terracing >5% slopes, and mixed terrace/bunds simulations : Surface
flow reduced to 12.4 and 11.3mm (45% and 50%)
• Terraces + Residue: decreases surface flow from 26mm to 16.8mm
(-25%) in July

22. Average Monthly Sediment Yield (1990-2012)
• Terrace + Residue mgt.: Sediment yields decrease from 1.03
tons/hectare in the base simulation to .47 tons/hectare in the month of
July (similar to steep terrace scenario)
• Terraces >5% slope and terrace + bund produce very similar results

23. Implications
• Average monthly runoff during the rainy season is the primary
driver to decreased sediment yield and surface flow.
• Simulations decrease surface runoff from 15% (terraces >20°) to
50% (terraces and bunds) and decrease erosion from 19% (residue
mgt. on all ag. fields) to 85% (terraces and bunds)
• Comprehensive investment of terraces and bunds maintained over
the simulation period (1990-2011) would decrease surface flow
50%, increase groundwater flow by 15%, and decrease erosion by
85%. (However, can achieve similar effects from constructing
terraces on slopes > 5% without bund construction)

24. Implications
• Residue management also has a significant effect on surface
flow and erosion in the Mizewa watershed.
– Average annual surface flow decreased 17% when adopting residue
management on all agricultural land and 26% when implementing a
mixed terracing and residue management.
• Simulated investments decrease surface runoff, AND increase
groundwater flow due to improvements in percolation.
• Groundwater flow is prolonged into dry months as well.
– Increased 8-32% in March
– Increased 13-52% in April
• Increased percolation may extend the crop growing period as
well which may have a direct effect on farmer livelihoods.

25. Conclusions
• Households investments on individual plot land require at
least 7 years of maintenance for significant benefits.
– Unlike technologies such as fertilizer or improved seeds, benefits
may accrue over longer time horizons.
• The longer one sustains SWC, the greater the payoff.
However, the individual benefits of sustaining SLWM on
private land may not outweigh the costs
– A mixture of strategies may reap quicker benefits
• May be necessary to think of a landscape / watershed
approach
– Understanding differences in agro-ecological zones, slope and soil
variations in order to plan most effective interventions
– Weigh benefits and costs of comprehensive SLWM approach,
possible opportunities to “phase-in” investments (i.e. terraces on
steep slopes first, then some residue management, etc.)

26. Cntd..Conclusions
• Decreases in average monthly runoff during the rainy season
is the primary driver to decreased sediment yield and surface
flow.
• Simulated investments decrease surface runoff, AND increase
groundwater flow due to improvements in percolation.
• Groundwater flow is prolonged into dry months as well.
– Increased 8-32% in March
– Increased 13-52% in April
• Increased percolation may extend the crop growing period
which may have a direct effect on farmer livelihoods.

27. Cntd..Conclusions
• Although simulations suggest that a landscape-wide approach may
reap the greatest long-term benefits, it is important to understand
the costs of such an investment.
• The economic impacts of SLWM interventions may be more
favorable in certain areas:
– Simulate long-term effects of complex ecological-economic systems are
necessary in order to inform policy decision and investments.
• Access to markets and infrastructure
• Off farm labor opportunities
• Land rental (agricultural and foraging rental)
• Link the household survey data and hydrological simulations
to model impact of different SLWM interventions, taking into
account socio-economic drivers and climate scenarios.

28. Cntd..Conclusions
• HH survey calculated SLWM benefits of improved water
capture and decreased erosion on private land
investment implicitly
• Hydrological model explicitly quantifies biophysical
improvements to water balance processes within the
watershed on agricultural land
• The type and amount of investment in SLWM has
different implications with respect to labor input and
utilization of agricultural land at household and
landscape level.