Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), Département des Sciences de la Terre et des Ressources Minières (STeRMi), Laboratoire du Génie Civil, des Géosciences et des Sciences Géographiques, BP 1093 Yamoussoukro, Côte d'Ivoire
The study area is the N'zo-Sassandra (West of Ivory Coast) watershed which is located between longitudes 7°15' and 8°05' West and latitudes 6°50' and 7°50' North. Its area is estimated at 4,310 km2. The objective of this study is to analyze the forecast of the flood flows of the N’zo (Sassandra) river located in the west of the Ivory Coast. The hydroclimatic data used (rainfall, ETP, flow) within the framework of this study extend on the one hand over the historical period (1961-2017) and on the other hand over the future period (2036-2065). The methodological approach adopted is based respectively on the analysis of past floods, the evaluation of the chosen rainfall-discharge model, the prospective climatic analysis and the prospective analysis of the flood flows. The variables used to describe the future evolution of these floods are the decennial and centennial quantiles of the annual maximum monthly mean discharges. Thus, an optimistic climate forecast scenario was used (RCP 2.6). This climatic scenario then fed into a hydrological rainfall-discharge model (GR2M model) calibrated to the reference period 1961-1990 and validated over the period 1991-2017. In response to climate forcing, future monthly flood discharges (QMXA) were simulated. The main results show that the best statistical law retained following the frequency analysis of the flood flows is the Gamma law which was used to estimate the frequency flows. The GR2M model evaluated, presented a good performance in calibration (79.7%) as in validation (82.7%) and demonstrated a great robustness (+3%) therefore a great capacity to reconstitute the flows of N'zo in Kahin. The climate forecast has shown a decrease in precipitation (-19.7%) and an increase in temperature (+1.6 °C) in the middle of the current century (2036-2065). The expected flood flow quantiles in the middle of the 21st century (2035-2065) are respectively 168.85 m3/s for the ten-year flow and 299.58 m3/s for the one-year flow. Thus, in response to climate change, the forecast of flood flows leads to a worrying drop in frequency flood flows, respectively of the order of 64.56% for the ten-year flood and 61.73% for the 100-year flood compared to their current values.
The objective of this study is to develop statistical models to predict the depth limit stop of water drilling in crystalline and crystallophyllian rocks using physical parameters of drilling. The study was conducted using data from physical parameters (depth of drilling, depth of the first water supply significant, alteration thickness and thickness of base drilled) from geological units of Archean and Paleoproterozoïcal domains of Ivory Coast. The methodology consisted of first analyze the physical parameters from the simple statistical features and frequency class distribution of these parameters. Then, a normalized principal components analysis (NPCA) was applied for the identification of explanatory variables relevant and expressive of drilling depth limit. Finally, a calibration was performed with a sample of 1,605 wells representing two thirds of the total sample to determine the coefficients of the linear regressions and the associated standard errors. The analysis of the distribution of physical parameters of drilling shows that only the depth of drilling is homogeneous (24.50%) with an average of 68.17 m. The most relevant and expressive variables for predicting the depth limit stop of water drilling in crystalline and crystallophyllian rocks are the depth of the first significant water arrival and the thickness of alteration. The errors associated with the regression coefficients generally low (below 1%) reflect the close relationship between the dependent variables and the explanatory variables. Two models for predicting the depth limit stop of water drilling (PROLIFE models) in crystalline and crystallophyllian rocks were developed.
The objective of this study is to develop statistical models to predict the drilling flow on rock aquifers. The study area is the former region of N'zi-Comoé (Central-East of Ivory Coast) that is located between longitude 3° 40' and 4°55' West and latitude 6° 20' and 8°10' North. The geological formations are composed of igneous rocks and metamorphic rocks. The methodology has been first applied to the approach of principal component analysis normalized, for identifying relevant and expressive variables of the drilling flow. Then, a calibration was performed with a sample of 100 drillings representing two thirds of the total sample to determine the coefficients of linear regressions and associated standard errors. Finally, an evaluation of the developed models was performed using the criteria of performance and robustness. The most relevant and expressive variables for modeling the drilling flow are the transmissivity, the thickness of healthy base drilled, the depth of the first significant water inlet and the total number of water inlet. Thus, two models were developed. Models assessment shows that they are performing with correlation coefficients ranging around 0.7, biases varying between 10-7 and 10-2 and quadratic errors in the order of 2.5 to 2.9. These models have also demonstrated their robustness with rates fluctuating between 3.2 and 5.3%. However, the model 2 is more efficient and more robust than model 1.