1. By Kudzai F. Ndidzano Limpopo Basin Development Challenge (LBDC)
Hydrological assessment of up-scaling rainwater harvesting techniques in Upper Mzingwane sub-catchment, Zimbabwe. By
Kudzai F. Ndidzano
Limpopo Basin Development Challenge (LBDC)

2. Research Background Mzingwane catchment characterized by
Smallholder communal farming area
Frequent droughts and long mid season dry spells
Water shortages in the root zone often lead to crop yield reductions, SSA maize yield <1ton/ha
Limited blue water resources
Isolated successes in rainwater harvesting (RWH) interventions
Need to assess the effect of wide scale adoption across a sub-basin level

3. Study Area Land Area = 7 700km2 Average Annual rainfall = 450mm
Mean Annual Runoff = 48mm (CV =118%)
Evaporation = mm
Mean Annual T°C : Min = 5°C and Max = 30°C (ZINWA, 2009)
Moderately shallow kaolinitic sands, very shallow to mod shallow sandy loams and clays and v shallow sands from basalts.

4. Objectives and Methodology
Identifying RWH techniques in practice
Literature review
Key Informant interviews
Reconnaissance survey
Investigating reasons for RWH adoption
Administered structured questionnaire
Focus group discussion
Determining upscaling RWH effect on runoff
RWH scenario development
Soil and Water Assessment Tool (SWAT) modeling

5. Modeling Scenarios’ Roughness Coefficients
Land surface characteristic
Median
Range
Conventional Farmers Practice (CP)
0.09
Min Tillage + No residue
0.07
Min Tillage ton/ha residue
0.12
Min Tillage ton/ha residue
0.3
The median Mannings’ roughness coefficients were substituted for the Overland flow roughness coefficient (OV_N) for the agriculture land use in the model’s Hydrological Response Unit (HRU) file to simulate each scenario. (Arnold et al., 2011)
Simulation results analyzed using the Paired Sample T-test for Comparison of Means using P = 0.05 significance level 5

6. Results

7. Obj. 1: Identified RWH practices
Mainly Conservation Agriculture (CA)
fertilizer micro-dosing
small plots averaging 0.5 ha
Isolated dead level contours with infiltration pits
Proportion of RWH to conventional farmers’ practice (CP) still fairly low (<35% of ward population).
CA Umzingwane Ward 13
Fertilizer microdosing

8. Obj. 2. Reasons behind adoption of Rainwater harvesting- Conservation Agriculture .
Rainwater capture, improved yields and draught power shortages and are the main drivers for CA practice

9. Objective 2 Cont…
CA was found to reduce runoff, soil erosion and draught power requirement while increasing yield, labour requirement

10. Objective 2 Cont…
Labour, weed control and crop residue management are the major challenges to CA adoption

11. Obj. 3. CA Scenarios Modeling results
Scenario Combination
Paired Differences t df
Sig.
95% Confidence Interval of the Difference
Mean
Std. Deviation
Std. Error Mean
Lower
Upper
Current v CP
.143
.356
.051
.0397
.246
2.78 47
.008
CP v Min Tillage + Min Residue
.006
.001
.0037
5.38
Current v Min Tillage + Min Residue
.149
.358
.052
.0452
.253
2.89
Current v Min Tillage + Max Resdue
.153
.364
.053
.0469
.258
2.91
Min Tillage + Max Residue v Min Till + Min Residue
-.004
.021
.003
-.0097
-1.14
Significant (P<0.05) runoff reductions between the CP and Current scenario against CA scenarios 11

12. Runoff Comparison under CA Scenarios
The simulated CA scenarios show significant (P<0.05) runoff reduction compared to the current scenario
Mutiga et al., (2011) also noticed moderate runoff reduction from RWH intensification in the Upper Ewaso Ngiro basin, Kenya

13. Conclusion and Recommendation
Conclusions
CA is the main RWH practice in Upper Mzingwane mainly to capture rainwater, improve soil moisture and crop yields.
Modeling results showed that up-scaling CA practices significantly (P< 0.05) reduces runoff
Recommendations
The study recommends physical field verification of runoff to confirm modelling results and further study on the effect up- scaling RWH on the downstream water requirements.
It is also recommended to capacitate farmers in overcoming CA challenges through mechanized systems, improved weed and pest management.

14. Expected Impact Increased evidence based CA adoption
Promotion of Mechanized CA techniques
Farmer capacity building

15. Thank you!!!