The document evaluates best management practices for reducing sediment load in the Blue Nile basin, analyzing the effects of improved rainwater productivity on downstream discharge and sediment concentration. It discusses the use of mathematical models to relate historical data with current predictions, highlighting the significant impact of land degradation on hydrology. The findings indicate that while erosion-control measures like terrace installation can reduce sediment, their overall effect on discharge is minimal, emphasizing the need for comprehensive land improvement strategies.

1. TAMMO S. STEENHUIS, DAWIT ASMARE, MOHAMMAD ENKAMIL, CHRISTIAN
GUZMAN, TIGIST Y. TEBEBU, HAIMANOTE BAYABIL, ASSEFA D. ZEGEYE, SEIFU
TILAHUN CHARLOTTE MACALISTER AND SIMON LANGAN
EVALUATING BEST MANAGEMENT PRACTICES FOR DECREASING
DOWNSTREAM SEDIMENT LOAD IN A DEGRADING BLUE NILE BASIN
NILE BASIN DEVELOPMENT CHALLENGE (NBDC) SCIENCE WORKSHOP
ADDIS ABABA, ETHIOPIA, 9–10 JULY 2013

2. What is the effect of improved rainwater
productivity in Ethiopia on the discharge
and sediment load downstream?

3. QUESTIONS TO BE ANSWERED
RAINWATER PRODUCTIVITY EFFECTS ON SEDIMENT AND DISCHARGE
What was the discharge and sediment
concentration in the past?
Is there a trend?
What will be discharge and concentration in
the future with improved rainwater productivity

4. PAST DISCHARGE AND SEDIMENT
CONCENTRATION TRENDS
Very little data available, therefore
• Use mathematical model to relate the existing
discharge and sediment concentrations with rainfall
• Assume that changes in parameters reflects trends
• Assume that the main impact on the hydrology and
sediment load is an increase in degraded areas in the
landscape
• Climate changes (that has been minimal over the past)
are included in the mathematical model

5. WHAT WE DID
Obtained discharge and sediment
concentration data for
Blue Nile at the Sudanese border
Gumura
Anjeni
Debre Mawi
Calibrated model to historical and recent data
Used historical parameters for current period
and visa versa to predict change

6. Parameter Efficient Distributed Model (PED model)
BASICS OF THE MODEL

7. Basics of Model:
Rainfall Intensities generally
greater than infiltration rates
for unsaturated soils
Debre Mawi

8. Maybar
Ethiopia
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0.00 0.20 0.40 0.60 0.80 1.00
Infiltrationrateorrainfallintensitycm/hr
Probabaility of Exceedance
Rainfall Intensity Lowest Infiltration Rate
Median infiltration rate

9. Model Basics
Consequently,
Only those areas that saturate
during storm produce runoff
 Regional groundwater rising to
surface in valley bottoms
 Degraded soils with shallow low-
permeable sub soils

10. 1
2
3
4
5
TESTING OF MODEL BASICS, DEBRE MAWI
Rainfall intensity vs.
storm runoff
R2 <0.4
Total rainfall vs.
storm runoff,
R2 > 0.59
Weeklyrunoff(mm)
Rainfall intensity Weekly precipitation

11. Location of runoff source and
infiltrating areas
Hill slope
Areas
Degraded soils
Saturated
Surface runoff
infiltration
interflow

12. RUNOFF PLOTS (MAYBAR)
SURFACE RUNOFF DECREASES
WITH STEEPNESS
16 37 43 64
slope of land
Runoff Coefficients

13. HYDROLOGY MODEL
There is a constant area for storm outflow after the
threshold is exceeded.
In the remaining part of the watershed, rain
infiltrates and becomes stream flow at some point
The threshold value can be obtained by simulating
a water balance. The threshold value is exceeded
when the soil exceeds field capacity.

14. EROSION MODEL
• Surface runoff interflow and baseflow from three areas
<30 days; 30 - 60 days >60 days
H = 1 H decreases 1→0 H=0

15. Model has been validated
in several small watersheds

16. GUMARA 1,500 KM2

17. 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1980 1985 1990 1995 2000 2005 2010
portionofwatershedarea
GUMARA: INPUT DATA
Well drained
hillsides
Max Stor Saturated Area 90 mm
Max Stor Degraded Area 30 mm
Max Stor Hillside 250 mm
base flow half life (t1/2) 20 days
interflow (τ*) 35 days
Degraded
Hillsides
Periodically saturated areas

18. 0
2
4
6
8
10
12
14
16
01/01/1987 01/01/1988 01/01/1989 01/01/1990 01/01/1991 01/01/1992
Discharge(mm/day)
Observed…
Predicted…
GUMARA WATERSHED
VALIDATION NS=0.6

19. GUMARA DISCHARGE
CALIBRATION 1981-1986 VALIDATION 1987-1992
y = 1.04x + 0.81
R² = 0.85
0
50
100
150
200
250
300
350
0 100 200 300 400
PredictedFlow(mm/month)
Observed Flow(mm/month)
y = 0.9237x + 1.692
R² = 0.8505
0
50
100
150
200
250
0 50 100 150 200 250
PredictedFlow(mm/month)
Observed Flow(mm/month)

20. GUMARA VALIDATION/CALIBRATION
SEDIMENT CONCENTRATION
1981-1992 1994 -2005
y = 0.9997x
R² = 0.8513
0
1
2
3
4
5
6
7
8
9
10
0 5 10
Predectedsedimentconc,g/L
Observed sediment conc, g/L
y = 1.03x + 0.22
R² = 0.85
0
1
2
3
4
5
6
7
8
9
10
0 5 10
PredictedSedimentconcentration(g/l)
Measured Sediment Concentration
(g/l)

21. 0
2
4
6
8
10
12
14
16
18Discharge(mm/day)
Observed flow(mm/day)
Predicted flow(mm/day)
degraded

22. GUMARA EFFECT OF DEGRADATION
4% DEGRADED SOIL VS 14% DEGRADED AREAS
Cumulative discharge Cumulative soil loss
0
1
2
3
4
5
6
7
8
9
Cumulativedischarge,m
Axis Title
not degraded
degraded
0
10
20
30
40
50
60
70
80
90
100
Cumulativesedimentsloss,Tons not degraded
degraded

23. BLUE NILE

24. Discharge 2003, degraded area = 0.22
Blue Nile watershed, 170,000 km2
0
50
100
150
200
250
300
350
400
450
5000
5
10
15
20
25
30
35
40
45
50
1-Jan-03
2-Mar-03
1-May-03
0-Jun-03
9-Aug-03
28-Oct-03
7-Dec-03
Preciptation(mm/10-days)
Discharge(mm/10-days)
2003 calibration 1993 calibration 1993 calibartion
Observed Precip
1960

25. SEDIMENT CONCENTRATION 2003 DEGRADED
AREA =0.22 BLUE NILE WATERSHED 180,000 KM2
0
50
100
150
200
250
300
350
400
450
5000
1
2
3
4
5
6
7
8
9
10
1-Jan-03
2-Mar-03
1-May-03
30-Jun-03
29-Aug-03
28-Oct-03
27-Dec-03
Preciptation(mm/10-days)
Sedimentconcentration(g/l)
Observed Predicted 2003
Predicted 1993 Precipitation

26. SEDIMENT CONCENTRATION 1993 DEGRADED AREA =0.18
BLUE NILE WATERSHED 180,000 KM2
0
50
100
150
200
250
300
350
400
450
5000
1
2
3
4
5
6
7
8
9
10
1-Jan-93
2-Mar-93
1-May-93
30-Jun-93
29-Aug-93
28-Oct-93
27-Dec-93
Preciptation(mm/10-days)
Sedimentconcentration(g/l)
Observed Predicted 1993 degr. frac. 0.18
Predicted 2003 degr. frac. 0.22" Precipitation

27. CUMULATIVE DISCHARGE BLUE NILE
SUDAN BORDER
0.0
0.5
1.0
1.5
2.0
1-Jan-98
1-May-98
29-Aug-98
27-Dec-98
26-Apr-99
24-Aug-99
22-Dec-99
20-Apr-00
18-Aug-00
16-Dec-00
15-Apr-01
13-Aug-01
11-Dec-01
10-Apr-02
8-Aug-02
6-Dec-02
5-Apr-03
3-Aug-03
1-Dec-03
CumulativeDischarge(m)
2003 degr frac 0.22
1993 degr frac 0.18
1963 degr frac 0.10
10% difference is equal to 6 BCM
which can irrigate 500,000 ha

28. CUMULATIVE SEDIMENT LOSS BLUE NILE
SUDAN BORDER
0
10
20
30
40
50
1-Jan-98
1-May-98
29-Aug-98
27-Dec-98
26-Apr-99
24-Aug-99
22-Dec-99
20-Apr-00
18-Aug-00
16-Dec-00
15-Apr-01
13-Aug-01
11-Dec-01
10-Apr-02
8-Aug-02
6-Dec-02
5-Apr-03
3-Aug-03
1-Dec-03
Cumulativesoilloss(Tons//ha)
2003 degr frac 0.22
1993 degr frac 0.18
1963 degr frac 0.10
Need more data

29. ARE THESE RESULTS
REASONABLE?
ALMOST NO EFFECT ON DISCHARGE
LARGE EFFECT ON SEDIMENT

30. ANJENI: TERRACES INSTALLED IN 1986 AND 1987
EFFECT ON DISCHARGE AND LAND USE

31. ANJENI INSTALLATION OF TERRACES 1986-1987
DISCHARGE
0
20
40
60
80
100
120
140
160
180
2000
5
10
15
20
25
30
31-Dec-83
26-Sep-86
22-Jun-89
18-Mar-92
13-Dec-94
8-Sep-97
4-Jun-00
DailyStreamFlow(mm/day)
Measured Flow
Predicted Flow
precipitation
Installation
of terraces

32. SEDIMENT CONCENTRATION AT WATERSHED OUTLET
0.00
10.00
20.00
30.00
40.00
50.00
60.00
5/31/1984
10/13/1985
2/25/1987
7/9/1988
11/21/1989
4/5/1991
8/17/1992
12/30/1993
Sedimentconcentration,g/l
Installation
of terraces

33. Rain water Management
Practices for Erosion
Control

34. EFFECT OF INSTALLATION OF TERRACES
•
• Virtually no effect on total runoff and distribution
between various discharge components
• Reduces sediment by what can be stored behind the
terraces. Once terraces are level, sediment
concentration are nearly back to old levels

35. EFFECTIVENESS OF
INFILTRATION FURROWS
AMOUNT OF SOIL SAVED IS
WHAT CAN BE STORED IN
FURROWS

36. PERMANENT PLANT COVER ON DEGRADED AREAS
This will stop erosion and provides income

37.  Preventing head cuts moving
upstream
 Shaping the gully below angle of
repose
 Planting trees around gullies
 Gully check dams

38. Planting Trees

39.  Only by reversing the degradation of the land
further increases in sediment load can be
prevented
 Structural soil and conservation measures are
only effective for a limited time to control
erosion
 Arresting gully formation will save land and
reduce sediment in streams
 No-till will conserve soil, but might increase soil
degradation due to increased pesticide use

40. Supporting Publications at
soilandwaterbeecornell.edu
Search for soilandwater Ethiopia Cornell