Hidrodinámica de los acuíferos karsticos de las sierras de Urbión y Neila (Burgos)

On the northern slopes of the Urbion and Neila Ridges there is a karstic system of Jurassic limestones and dolomites in a monoclinal arrangement, bounded above and below, respectively, by the impermeable series of the Keuper and Weald. Recharge is by infiltration of rain and meiting snow as well as from the outflow of numerous streams. Discharge flows towards the springs of the young Rivers Najerilla (198 l/s) and Arlanza (500 l/s). An interesting point is an underground transfer at Urbion of 14 hm 3 /yr from the basin of the Ebro to that of the Duero. According to water-tracing tests, during low flow periods, the average water velocity in the aquifers is between 27 and 38 m/h, and 160 rn/h near the outlet. A simulation in 1990-1991 of the hydrographs of the springs using a rainfall runoff model provided a detailed hydrological balance in which the importance of upstream turbulent flow was evident. The net recharge of precipitation was 42-43 %, though this varied considerably with the seasons.