Practical risk assessment for embankments, dams, and slopes - Risk and Reliability in Geotechnical Engineering - page 436

Table 11.2 Probability estimates

Probability of failure from internal
erosion

Incremental
annual
probability
pool elevation
(IPP) ≥

Annual
probability
pool elevation
(PP) ≥

Existing
conditions

After remedial
measures Peak pool elevation (PPE) in feet

467 (Dry reservoir—no flow) 1.0000 0.0

1.5 × 10 − 06 1.0 × 10 − 07

480 (Operational pool) 1.00000 0.00425

4.0 × 10 − 06 1.5 × 10 − 07

494 (Conservation pool) 2.0 × 10 − 05 4.0 × 10 − 07 0.99150 0.02873

498 (Seasonal pool) 3.0 × 10 − 05 5.1 × 10 − 07 0.94255 0.05854

500 0.87442 0.08201

5.1 × 10 − 05 5.8 × 10 − 07

505 0.77852 0.10164

7.3 × 10 − 05 7.3 × 10 − 07

510 9.4 × 10 − 05 9.2 × 10 − 07 0.67115 0.12772

515 0.52308 0.12383

1.2 × 10 − 04 1.3 × 10 − 06

520 0.42348 0.10894

1.4 × 10 − 04 1.6 × 10 − 06

525 1.6 × 10 − 04 2.0 × 10 − 06 0.30519 0.08123

530 (Seepage observed downstream) 1.8 × 10 − 04 2.6 × 10 − 06 0.26103 0.06266

535 0.17987 0.07601

6.0 × 10 − 04 3.4 × 10 − 06

540 0.10902 0.05224

1.0 × 10 − 03 4.3 × 10 − 06

545 1.5 × 10 − 03 5.6 × 10 − 06 0.07539 0.02477

550 0.05947 0.01273

4.2 × 10 − 03 7.0 × 10 − 06

555 0.04993 0.00937

6.9 × 10 − 03 9.2 × 10 − 06

560 9.6 × 10 − 03 1.3 × 10 − 05 0.04073 0.01087

565 1.2 × 10 − 02 1.6 × 10 − 05 0.02819 0.01486

570 0.01100 0.01035

1.5 × 10 − 02 2.0 × 10 − 05

575 (Top of seepage blanket) 0.00750 0.00300

1.0 × 10 − 01 2.6 × 10 − 05

580 1.5 × 10 − 01 3.4 × 10 − 05 0.00500 0.00240

585 0.00270 0.00175

2.2 × 10 − 01 4.2 × 10 − 05

590 0.00150 0.00094

2.8 × 10 − 01 5.7 × 10 − 05

595 3.5 × 10 − 01 7.6 × 10 − 05 0.00082 0.00054

0.00042 0.00030

600 4.2 × 10 − 01 1.2 × 10 − 04

605 0.00022 0.00014

4.8 × 10 − 01 1.9 × 10 − 04

608 (Top of embankment) 0.00014 0.00006

5.5 × 10 − 01 5.0 × 10 − 04

611 (Top of parapet wall) 9.0 × 10 − 01 1.5 × 10 − 03 0.00010 0.00007

Table 11.3 Pool elevation vs. potential loss of life
Pool elevation in feet Potential loss of life estimate

494 23

498 27

500 35

505 62

525 100

550 300

575 339

611 370