FLOODS IN LORCA (MURCIA): HAZARD AND EXPECTATION

Abstract

The severe consequences produced by river Guadalentín overflowing exceptionally as it passes Lorca. have had repercussions. almost from the beginning of its history. on the economic life and the managers' enterprise of the city. The historical floods of San Calixto or Santa Teresa have been followed by nowadays' spills. occurred on October the 22nd 1948. and on the days 18^th and 19^th of October 1973; the latter having had a maximum instantaneous volume of 2.054 m' per second. as it went out of the reservoir of Puentes. causing. thus, a great number of damages. The frequency distributions log-Gumbel and log-Pearson Type III used as models of prediction. do confirm the figures obtained at Puentes by means of Fisher's procedure of maximum probability and the square-minimum based one; the results being. for recurrent periods of 100 caudal years a daily maximum average of 306-314 m' per second. and for instantaneous periods one of 2.000 m' per second. Some of the most relevant factors which have generated the floods are the phenomenon called gota fria through retrogression, together with the important effect of disparo or orographic elevation of unsteady humid air, linked to the very same morphostructural features of the river basin and its particular drainage geometry: high reliefs, deep erosion, basins fitted along their headwaters, the webbed shape of the hydrographic network that favours the simultaneity of flooding waves, and, nowadays, the insuficient rolling capacity of the reservoirs due to their being earthed up The fragility of the environment. the high quantity of damages. as well as the nature and state of the defensive works have become value judgements that nowadays, more than ever, also due to a greater degree of information, denote certain pessimism among the in habitants of Lorca and its fertile irrigated area.