RESULTS The following runs were accomplished: Series A   Flood discharges for 2-, 5-, 10-, 25-, 50-, 100-, 200-, 500- and 1000-yr return periods, specifying the maximum average monthly level as initial condition in Morena and Barrett Dams. Series B  Same as above, but assuming zero infiltration in the channelization project reach, in order to evaluate the impact of a possible concrete channel upon the aquifer recharge. The results of Series A are shown above. The difference between lines 6 and 5, shown in line 7, corresponds to the local contribution of the channelization project reach. Line 8 shows the adopted flood discharge. The results of Series B are shown below. From this table it is concluded that the mean annual discharge, corresponding to the 2-yr return period, feeds 0.459 hm3 to the groundwater table along the channelization reach. This constitutes 4.6 percent of the flood runoff volume. The concrete channel would keep this volume in the surface runoff, and would increase the peak discharge by 6 m3/s. In contrast to the volume drained during the flood, the mean annual runoff of Arroyo Alamar has been calculated as 65.416 hm3. Likewise, the volume of water extracted annually from the aquifer of the Tijuana river basin, including Alamar Creek, is 13.8 hm3. Assuming for the mean annual runoff a conservative value of infiltration volume equal to that of the mean annual flood (2-yr return period), the postulated channelization would avoid that an annual volume equal to [(4.6)(65.416)/100] = 3.01 hm3 will feed the ground water. This quantity represents [(3.01/13.8) 100] = 22 percent of the groundwater resources of all the Tijuana region, which is a substantial quantity.