# Inflow Scenario Generation for the Ethiopian Hydropower System

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Area, Data, and Materials

^{2}and an elevation of 1787 m. The lake serves as the reservoir of the Beles hydropower plant with seven spillway gates called Charachara Gates. The spilled water at Charachara is used partly for the Tis Abay fall(Tis Esat, tourist attraction) and partly for power generation at Tis Abay I and II. However, there is yet to be available data about the percentage of water that will be used for power production. Therefore, we treat the Tis Abay I and II power plants as run-of-the-river throughout this study. As a result, we have eight reservoirs, and the generation largely depends on the maximum reservoir level attained during the rainy season (July to September).

- Plant’s unique characteristics in relation to the water level (Gibe 1, Gibe 2, and Gibe 3)
- Load forecast and history of generation.
- Downstream facilities (Beles, Fincha, and Koka)

#### 2.2. Methods

#### 2.2.1. Estimation of Historical Inflow Time Series

^{3}/s of water released during one hour.

#### 2.2.2. Time Series Analysis and Stochastic Model Estimation

#### Daily Time Resolution

#### Weekly Time Resolution

#### 2.2.3. Residual Diagnosis

#### Daily Time Resolution

#### Weekly Time Resolution

## 3. Result and Discussion

#### 3.1. Synthetic Historical Inflow Time Series

#### 3.2. Scenario Generation

#### 3.2.1. Daily Time Resolution

#### 3.2.2. Weekly Time Resolution

#### 3.3. Evaluation of the Generated Inflow Scenarios

## 4. Conclusions and Recommendations

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

ACF | autocorrelation function |

AR | autoregressive |

ARFIMA | autoregressive fraction integrated moving average model |

ARIMA | autoregressive integrated moving average |

DAV | data access viewer |

DOF | degree of freedom |

EEP | Ethiopian Electric power |

GIS | geographic information systems |

MA | moving average |

MAE | mean annual energy |

MAI | mean annual inflow |

NEXRA | Next Generation Weather Radar |

PAR | periodic autoregressive |

PARMA | periodic autoregressive-moving average |

PRMS | precipitation-runoff modeling system |

SARIM | seasonal autoregressive integrated moving average model |

SDDP | stochastic dual dynamic programming |

SWAT | surface water assessment tool |

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**Figure 2.**Historical pattern of water levels for Gibe 1, Gibe 3, Koka, and Tekezé reservoirs; source: EEP.

**Figure 8.**Actual water level versus synthetic inflow in 2015–2016 and 2018–2019 for Gibe 1 and Tekezé reservoirs.

**Figure 13.**Actual and simulated load shedding and generation schedule for sample reservoirs in April.

**Figure 15.**Actual reservoir content plus simulated reservoir content and spillage for the tree cases.

Power Plant | Coordinates °N, °E | Dam Height (m) | Maximum Level (m a.s.l) | Storage (Mm ^{3}) at Max. Level | Installed Capacity (MW) | Maximum Discharge (m ^{3}/s) | Average Energy (GWH) |
---|---|---|---|---|---|---|---|

Beles | 11.82, 36.92 | 35.00 | 1787.00 | 37,307.00 | 460.00 | 160.00 | 1867.00 |

M.Wakena | 7.225, 39.462 | 42.00 | 2522.90 | 875.00 | 153.00 | 60.00 | 543.00 |

Fincha | 9.789, 37.269 | 22.20 | 2219.00 | 964.00 | 134.00 | 29.68 | 760.00 |

Gibe I | 7.831, 37.322 | 41.00 | 1,671.55 | 863.00 | 210.00 | 100.00 | 722.00 |

Gibe II | 7.757, 37.562 | 46.50 | Diversion Weir | - | 420.00 | 98.12 | 1635.00 |

Gibe III | 6.844, 37.301 | 243.00 | 892.00 | 15,500.00 | 1870.00 | 2200.00 | 6500.00 |

Koka | 8.468, 39.156 | 23.80 | 1599.00 | 4250.00 | 42.00 | 144.00 | 110.00 |

Awash II | 8.468, 39.156 | river | run-of-river | - | 32.00 | 65.60 | 182.00 |

Awash III | 8.468, 39.156 | river | run-of-river | - | 32.00 | 66.20 | 182.00 |

Tekezé | 13.348, 38.742 | 188.00 | 1140.10 | 9310.00 | 300.00 | 184.00 | 1393.00 |

Am. Neshe | 9.789, 37.269 | 38.00 | 2232.50 | 526.10 | 97.00 | 18.70 | 35.00 |

Tis Abay I | 11.486, 37.587 | river | run-of-river | - | 12.00 | 114.00 | 33.70 |

Tis Abay II | 11.486, 37.587 | river | run-of-river | - | 72.00 | 114.00 | 359.00 |

Null Rejected | p-Value | Test Statistic | Critical Value | |
---|---|---|---|---|

1 | false | 0.27408 | 23.3047 | 31.4104 |

Parameter | Value | Standard Error | T Statistic | p Value |
---|---|---|---|---|

Constant | 0 | 0 | ||

MA{1} = ${\theta}_{1}$ | −1.403 | 0.045174 | −31.0574 | 9.0611 $\times {10}^{-212}$ |

MA{2} = ${\theta}_{2}$ | 0.28348 | 0.085036 | 3.3336 | 0.00085725 |

MA{3} = ${\theta}_{3}$ | 0.1482 | 0.058094 | 2.551 | 0.010741 |

SMA{1} = ${\Theta}_{365}$ | −0.77234 | 0.064318 | −12.0081 | 3.2218 $\times {10}^{-33}$ |

SMA{2} = ${\Theta}_{730}$ | 0.014517 | 0.070344 | 0.20637 | 0.8365 |

Variance | 3.0546 $\times {10}^{9}$ | 3.1855 $\times {10}^{-12}$ | 9.5891 $\times {10}^{21}$ | 0 |

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**MDPI and ACS Style**

Dires, F.G.; Amelin, M.; Bekele, G. Inflow Scenario Generation for the Ethiopian Hydropower System. *Water* **2023**, *15*, 500.
https://doi.org/10.3390/w15030500

**AMA Style**

Dires FG, Amelin M, Bekele G. Inflow Scenario Generation for the Ethiopian Hydropower System. *Water*. 2023; 15(3):500.
https://doi.org/10.3390/w15030500

**Chicago/Turabian Style**

Dires, Firehiwot Girma, Mikael Amelin, and Getachew Bekele. 2023. "Inflow Scenario Generation for the Ethiopian Hydropower System" *Water* 15, no. 3: 500.
https://doi.org/10.3390/w15030500