Final Interventions Report - DWA Home Page

More documents

Recommendations

Info

Water Reconciliation Strategy Study for the Large Bulk Water Supply Systems: Greater Bloemfontein Area 39 2. STUDY METHODOLOGY The study was done on the bases of quaternary catchments. The quaternary catchment shape files were used to create the following: Group cultivation land per catchment, with base data from the Agricultural geo-referenced information system. Farm boundaries per catchment. Rivers, streams and dams per catchment. By using the rivers and streams layer a 3 km buffer zone on both banks were created. The digitised cultivation land layer was reduced to the buffer zone. The digitised cultivation land was further reduced by selecting the pivots (round circles) and deselecting cultivation lands bigger than 10 ha. This was done because the practice of irrigation without pivots on bigger than 10 ha is highly unlikely. The following assumptions were made: No water is pumped more than 3 km from a river or stream. Centre pivots are irrigation. No irrigation are done on cultivation lands bigger than 10 ha excluding pivots. No dams were taken in consideration. 3. STUDY FINDINGS The results are presented on Figures A.1 to A.7 in Annexure A. Table 3.1 gives the extent of the irrigation in the Catchments according to the WARMS data, pivot irrigation and other irrigation. Table 3.1: Irrigation in the Quaternary Catchment Areas Quaternary Catchment Area WARM S Irrigation in ha Confidence level % Pivots Other Total Pivots Other C52A 612 218 2 951 3 169 90 60 C52B 421 0 1 087 1 087 90 60 C52C 237 38 910 948 90 60 C52D 298 15 1 453 1 468 90 60 C52E 779 378 3 449 3 827 90 60 C52F 1 957 649 2 014 2 663 90 60 Total 4 304 1 298 11 864 13 162 4. OBSERVATIONS DURING THE STUDY The following observations were made during the study: There are surface dams in the area and there are a tendency that irrigation are developed around these dams. Because of these assumptions, about 5 % of the total irrigation were not captured. The confidence level that pivots are irrigation are high. The 90 % confidence is because the mapping was done by other persons in 2008. New irrigation development was possible and was not measured. The confidence level of assumed irrigation are only 60 %. The confidence level of this can be higher if satellite images of two or more seasons are available to verify the cultivation patterns. The area of assumed irrigation will reduce by about 20 to 40 % when the cultivation patterns are known. Some of the WARMS data allocated to a Quaternary Catchment area, projected outside the Catchment. This will be rectified with the verification and validation process. Dam information also needs to be more accurate. Interventions Report June 2012
Water Reconciliation Strategy Study for the Large Bulk Water Supply Systems: Greater Bloemfontein Area 40 5. FARM DAM LOSSES The catchment areas contain a number of private farm dams. Losses out of farm dams due to evaporation were not taken into account. 6. NEXT STEPS TO IMPROVE ON THE CONFIDENCE In order to further improve on the confidence level of the study a recent Landsat 7 or Spot satellite image of the area for two or more seasons are needed. This will be used to: 1. See if there are new developments. (Satellite image from DWA) 2. Improve on the split between irrigation and dry land fields. 3. Site visits to verify 20% of the largest areas. 4. Summary of above information in a report, tables etc and persent at a meeting. As a test to determine the accuracy of the assumptions a satellite image dated 2008-08-16 for Catchment C52A was used to identify irrigation more accurately. Out of this the following was determined: No cultivated land bigger than 10 ha indicate possible irrigation. By using the satellite image to select cultivated lands smaller than 10 ha, next to dams and rivers, the area of proposed irrigation changed from 2 951 ha to 1 427 ha. The satellite image was for a winter season, where this is a summer planting region and a January or February image will give a better indication. This 52 % reduction in proposed irrigation show the importance of the satellite image test to the data. 7. WATER USE BY THE IRRIGATION The type of crop planted in a particular area is the most important factor influencing the quantity of water required for irrigation. In order to estimate the water use by the irrigation the type of crops need to be established. This can only be done with a visit to the site. The other important issue is whether they plant one or two crops in a year. Out of the WARMS data the water use calculated to be between 4 616 m3/ha/year to 8 868 m3/ha/year. If the crops are known PLANWAT can be used to calculate the crop water requirement per Quaternary Catchment Area. Whilst on the one hand the selection of alternative crop types could reduce water requirements, the potential income must also be taken into account. Planting low value “thirsty” crops in water scarce areas should be avoided. 8. IMPROVEMENT FOR CATCHMENT C52A A recent Spot 5 satellite image was obtained from the Department of Water Affairs. Unfortunately the date of the image is not known and therefore the season is not known. 8.1 See i f there are New Developments (Satellite Image From DWA) No new developments were observed on the Satellite image between the new image and the one dated 2008-08-16. 8.2 Improve on the Split Between Irrigation and Dry Land Fields The satellite image for Catchment C52A was used to split the irrigation and dry land fields. All fields in Catchment C52A that shown green was digitised and the area was determined. This area exclude the pivot irrigation. Interventions Report June 2012
Page 2: Water Reconciliation Strategy Study
Page 5 and 6: Water Reconciliation Strategy Study
Page 47: Water Reconciliation Strategy Study
Page 99 and 100:
Water Reconciliation Strategy Study
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
Page 295 and 296:
Page 297 and 298:
Page 299 and 300:
Page 301 and 302:
Page 303 and 304:
Page 305 and 306:
Page 307 and 308:
Page 309 and 310:
Page 311 and 312:
Page 313 and 314:
Page 315 and 316:
Page 317 and 318:
show all

Final Interventions Report - DWA Home Page

Create successful ePaper yourself

Delete template?

Save as template?