THROUGHFALL IN FOREST STANDS 137 



gauge. The two remaining gauges were designed by Prof. Thorn at 

 Oxford, and have an aerodynamic profile which was shown in wind-tumiel 

 tests to give only a 6% increase in wind speed immediately above the 

 collecting area ; these gauges have two concentric compartments of equal 

 area, to provide internal comparison. In one of the gauges, these chambers 

 are each shghtly smaller than the 5-in. gauge, and in the other, rather larger ; 

 in both there is an outer guard chamber. In open ground 350 yds from 

 the plot, a recording rain gauge and two 5-in. gauges are exposed in the 

 standard mamier. As expected, there were differences in catch between 

 gauges of the same type located in different places, and between the various 

 types of gauge. Over several months, the gauges provided with Nipher 

 shields agreed with the standard ground level gauges to within 1%, while 

 the catches of the unshielded elevated gauges, the Alter gauges and the 

 larger aerodynamic gauge were lower by about 2%. It should be pointed 

 out that the conditions in this plantation were far less exposed than in that 

 of Law. 



Data for selected storms occurring in autumn i960, have been examined 

 by multiple regression teclmiques. Up to half the variabihty between 

 different types of gauge could be attributed to, or was associated with, 

 variables which might be expected to affect evaporation from the gauge, or 

 aerodynamic factors affecting gauge catch (wind velocity, temperature, 

 etc. measured at the centre of the plot above the trees). 



It is difficult, if not impossible, to distinguish between local variations of 

 true rainfall and other local climatic variations which effect gauge efficiency. 

 However, the regression approach shows some promise in assessing the 

 capabilities and limitations of the various gauges which might be used to 



Table 6 

 Stem flow, trough catch, incident precipitation and interception. (Inches) 



Period Stem Trough Total Gross 



1959 flow catch throughfall precipitation Interception 



10-6 -24-7 0-02+ 0-005 i-o8± 0-059 I-I0+ 0-060 



24-7-30-7 0-03 ±0-005 0-70+ 0-046 0-7010-046 



30-7-14-8 o-07±o-oi2 i-3i±o-o86 i-3i±o-o86 



14-8 -22-10 0-06+0-0I0 0-84+0-054 0-84+0-054 



22-10-4-11 0-05+0-010 o-65±o-033 0-6510-034 



4-11-18-11 0-06+0-012 o-68± 0-033 0-68 + 0-035 



24-7 -18-11 0-27+0-046 4-20+0-230 4-4610-240 6-09 1-64 



