Geoscience Reference
In-Depth Information
Based on the area of the watershed, runoff coefficient result and long time
average of rain data, we been able to estimate the total potential of urban storm
water. Over a number of years, the average urban runoff potential has been
approximately 1.5 MCM (million cubic meters) and 2.0 MCM for Herzliya and
Ra'anana respectively. In practice, the quantity available for use is much smaller
and can reach only several hundred thousand cubic metre, since not all the drainage
systems are connected to one outlet or there are local limitations. Therefore the
entire quantity of potential urban runoff cannot be captured directly by means of
engineering installations. Rather each case must be examined separately in accor-
dance with the draining of the various basins.
5.5 Urban Storm Water Quality from Various Land Uses
5.5.1 Major Ions, Nitrates, BOD (Biological Oxygen Demand)
and Total Suspended Sediments (TSS)
The range, mean concentration and standard deviation of urban storm water from
the various land uses are presented in Table
5.3
. The sulfate concentrations were
found to be similar in industrial areas to the concentration observed at the residen-
tial area. Concentrations of BOD were higher in the industrial land uses areas than
in the residential areas. Salt concentrations on the road and parking lot were the
lowest - and in the authors' opinion - demonstrate the short length of the flow path
(less than 200 m), and not the nature of the land use. Despite the fact that in the
industrial areas the concentrations of BOD does not surpass the standard, the values
found were very close to it.
The mean concentration of Chloride and Nitrate in urban storm water from
residential area is very low (22.3 and 3.6 mg/L respectively). The chloride and
nitrate values were significantly lower than the values in the local aquifer water
(253 and 53 mg/L respectively for chloride and nitrite). It is reasonable to suppose,
therefore, that the recharge of this water would improve the quality of the local
aquifer were. Similar observations regarding saline concentrations in urban runoff
water were found in Ashdod and Rishon Lezion (Maniv, unpublished Water quality
data).
5.5.2 Heavy Metals
Figure
5.6
shows a comparison of the heavy metal concentration values observed in
the residential areas, industrial areas, and major roads. It can be seen from this data
that overall at residential areas storm water contained low concentrations of trace
metal. It should be pointed out that the larger portion of is expected to be in the
adsorbed phase due to the natural partition under aerobic condition. Higher
