The Balochistan Water Resources Development Sector Project (BWRDSP), financed under ADB Loan 3700-PAK (COL), is a flagship project of the Government of Balochistan to improve water security in the Zhob and Mula River basins. The project’s interventions—including flood protection bunds, irrigation headworks, diversion weirs, and infiltration galleries—were designed using updated hydrological frequency analyses (rainfall datasets up to 2022), ensuring that design floods reflected the most recent extreme events.
The catastrophic monsoon events of
2022 and 2024 provided a test for the project. Despite rainfall reaching 239%
above normal in Balochistan and 318% above normal in Sindh in 2024, BWRDSP
schemes withstood flood discharges nearly 70% above their original design
capacity, confirming their climate resilience.
This paper establishes resilience on two fronts:
o
Flood resilience – capacity to safely pass ~60,000 cusecs in 2024 despite
being designed for ~35,000 cusecs.
o Drought resilience – infiltration galleries at Killi Sardar, Hitachi, and Kharzan Churri, which recharge aquifers and ensure water availability during extended dry periods.
2. Hydrological Analysis and Flood Magnitudes
2.1 Rainfall Frequency Analysis (Updated 2022)
Updated frequency analyses (Kalat:
1971–2022, Khuzdar: 1980–2022) showed an approximate 12% increase in extreme
rainfall depths after incorporating recent events.
Table 1: Updated
Rainfall Depths – Khuzdar Station
|
Return Period (yrs) |
Depth (mm, 1980–2018) |
Depth (mm, 1980–2022) |
% Increase |
|
10 |
56.1 |
60.9 |
+8.5% |
|
50 |
73.6 |
81.5 |
+10.7% |
|
100 |
81.0 |
90.3 |
+11.5% |
|
500 |
98.1 |
110.4 |
+12.5% |
Table 2: Updated
Rainfall Depths – Kalat Station
|
Return Period (yrs) |
Depth (mm, 1971–2018) |
Depth (mm, 1971–2022) |
% Increase |
|
10 |
57.1 |
60.6 |
+6.1% |
|
50 |
82.3 |
89.4 |
+8.6% |
|
100 |
93.0 |
101.6 |
+9.2% |
|
500 |
117.6 |
129.7 |
+10.3% |
2.2 Design Flood Estimates for Key Schemes
Table 3: Design
Floods (Updated)
|
Scheme |
1:50 Yr (cusecs) |
1:100 Yr (cusecs) |
1:500 Yr (cusecs) |
1:1000 Yr (cusecs) |
PMF (cusecs) |
|
Siri Toi Dam |
39,320 |
45,760 |
60,890 |
67,250 |
172,720 |
|
Karkh Irrigation Scheme |
30,980 |
36,480 |
49,340 |
55,090 |
74,620 (10k yr) |
|
Kharzan–Hitachi Scheme |
89,300 |
106,300 |
146,900 |
164,800 |
225,400 (10k yr) |
2.3 Observed 2024 Floods vs Design Floods
·
Observed Peak (2024): ~58,950 cusecs (Mula Basin).
·
Comparison:
o
Karkh Scheme:
observed = 1.6 × 1:100 year flood (36,480 cusecs).
o
Siri Toi Dam:
observed ≈ 1:500 yr flood (60,890 cusecs).
o
Kharzan–Hitachi:
observed within 1:50–1:100 yr envelope.
This shows the 2024
flood was well within updated design thresholds and validates the conservative
hydrological basis.