מציאת מקדם הנגר העירוני בסביבה העירונית של חיפה

In order to examine the rainfall-runoff relation in the city of Haifa, two level gauges were placed in the channels of the Technion watershed (0.24 sq.km), and of the Upper Hadar watershed (0.65 sq.km). In addition, discharge data from the Qiryat Eliezer watershed (0.34 sq.km) were obtained from the Hydrological Service of Israel. A discharge curve was elaborated on the basis of hydrological data collected between 2001/03-2003-04, and records of flow events during the research period. The increment of the gauged rainfall-intense data enabled the reconstruction of rainfall-runoff correlations for the sampled events. The linear regression derived from 250 hydrographs showed a correlation between rainfall depth and runoff, and between rainfall depth and runoff coefficients, for all the examined flow events. The research used geographical information systems (GIS) for classifying the watersheds according to feature elements (natural cover, roads, roofs, parking lots), in order to compare the impervious surfaces to runoff yields and peak discharges. The main runoff contributor was found to be directly connected to impervious areas, such as roofs connected to paved surfaces. For peak discharges it was found that all areas fitting this definition were runoff contributors, whereas for average flow events only 60%-75% of these areas (directly connected impervious area) contributed to runoff. The natural surface contribution of the Technion and Upper Hadar watersheds was negligible, since their runoff coefficient proved lower than the relative parts of the directly connected impervious area. The Qiryat Eliezer watershed, possessing a built drainage system that also collects stormwater from permeable surfaces, presented a different picture, since in some flow events the runoff coefficient was higher than the relative portion of the directly-connected impervious areas.