1 Introduction
2 Groundwater System of Lake Naivasha Area
2.1 Groundwater Models for Lake Naivasha Area
3 Methods and Data
3.1 Conceptual Model on Historical Data
McCann (1974) | Gaudet and Melack (1981) | Åse et al. (1986) | Becht and Harper (2002) | van Oel et al. (2013) | Range (± extreme values) | Modelled – natural situation | Modelled – abstraction at FBP | ||||
---|---|---|---|---|---|---|---|---|---|---|---|
Hydrologic budget [Mm3/yr] | Various years | 1973–1975 | 1972–1974 | 1978–1980 | 1932–1981 | 1965–1979 |
High bed leakance |
Low bed leakance |
High bed leakance |
Low bed leakance | |
Total inflow | 380 | 337 | 279 | 375 | 311 | 353 | 340 ± 70 | 342.3 | 339.6 | 342.8 | 339.3 |
Precipitation | 132 | 103 | 106 | 135 | 94 | 123 | 116 ± 20 | 116.0 | 116.0 | 116.0 | 116.0 |
River discharge | 248 | 234 | 148 | 215 | 217 | 230 | 215 ± 50 | 215.0 | 215.0 | 216.0 | 216.0 |
Groundwater seepage | –a
| –a
| –a
| –a
| –a
| –a
| 11.3 | 8.6 | 10.8 | 7.3 | |
Total outflow | 380 | 368 | 351 | 341 | 312 | 362 | 352 ± 80 | 345.5 | 339.6 | 347.0 | 339.4 |
Evapotranspiration incl. swamp | 188 | 312 | 284 | 288 | 256 | 328 | 276 ± 90 | 276.0 | 276.0 | 276.0 | 275.0 |
Groundwater seepage | 34a
| 56a
| 67a
| 53a
| 56a
| 34a
| 50 ± 20 | 69.5 | 63.6 | 71.0 | 63.5 |
Discrepancy: | −3.2
|
−0.0
|
−4.2
|
−0.2
| |||||||
Characteristics | |||||||||||
Lake stage [m] | 1887.01 | 1887.03 | 1887.00 | 1886.95 | |||||||
Lake area [km2] | 115.65 | 115.55 | 115.51 | 115.29 | |||||||
Lake volume [Mm3] | 462.30 | 459.74 | 458.90 | 453.64 |
Literature – natural situation | Modelled – natural situation | Modelled – abstractions at FBP | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Hydrologic budget [Mm3/yr] | McCann (1974) | Gaudet and Melack (1981) | Åse et al. (1986) | Clarke et al. (1990) | Ojiambo et al. (2001) | Various sources / estimate | Range (± extreme values) |
High bed leakance |
Low bed leakance |
High bed leakance |
Low bed leakance |
Total inflow | 135 ± 100 | 162.4 | 156.6 | 163.9 | 156.5 | ||||||
Recharge | – | – | – | – | 450 | 0–130b
| 80 ± 50 | 85.0 | 85.0 | 85.0 | 85.0 |
Lake seepage | 34a
| 67a
| 53a
| – | – | 30–70 | 55 ± 50 | 69.5 | 63.6 | 71.0 | 63.5 |
River | – | – | – | – | – | unknown | unknown | 7.9 | 8.0 | 7.9 | 8.0 |
Total outflow | 95 ± 75 | 162.4 | 156.6 | 165.3 | 158.3 | ||||||
Lake seepage | – | – | – | – | – | – | – | 11.3 | 8.6 | 10.8 | 7.3 |
Constant head boundary North | 39 | 37–51 | 0 | 5–25 | – | 0–60 | 35 ± 25 | 49.2 | 30.9 | 49.0 | 30.6 |
Constant head boundary South | – | 18–76 | 46–56 | 27–270 | 18–50 | 18–270 | 60 ± 50 | 102.0 | 117.1 | 102.0 | 117.0 |
Wells | 3.5 | 3.5 | |||||||||
Discrepancy: | −40 ± 175 | 0.0 | 0.0 | −1.4 | −1.8 |
3.2 Numerical Model
3.3 Calibration and Validation
4 Results
4.1 Calibration
Error metric |
High bed leakance |
Low bed leakance | ||
---|---|---|---|---|
Value 60 observations | Value 52 observations | Value 60 observations | Value 52 observations | |
RMS [m] | 16.13 | 6.81 | 16.28 | 7.43 |
MAE [m] | 9.22 | 5.32 | 9.61 | 5.82 |