WORKING GROUP 3 
VAN DER MEER 
197 
for agricultural production after execution of the agricultural and civil engineer 
ing works. The land classification for reclamation can only be made when 
all experts dealing with the problem have made their calculations and the team 
together can compose the tables of costs and benefits. This often reveals that 
the reclamation of potentially good soils will be very expensive, with an un 
favourable cost-benefit ratio, and that soils with a lower agricultural potential 
show more favourable aspects. 
A few examples will be discussed, showing how external, non-pedological 
features, may determine the development of certain areas with good soil 
potentialities. Some of these features might perhaps be partly determined from 
the aerial photographs, but very often this is not possible. 
Climate 
It is a good practice in a soils report to give a picture of the average climatic 
conditions of the area investigated. This is justified, because climate is an im 
portant factor influencing the development of soils. Such a climatic average, 
however, does not say much for the problems to be tackled in a development 
project. For the project design, the project engineer must analyse the climate 
and give calculations based on the frequency of certain climatic factors {e.g. 
rainfall). He thus has to be aware of the hazards of extremes which, when they 
occur, exceed the figures on which his calculations are based. In this respect the 
rainfall figures in the Far East are very interesting. Figures of the Republic of 
Korea may serve as an example. 
A study of the weather station at Mokpo, on the south-west coast, shows very 
pleasant average figures. The annual precipitation is about 1200 mm, regularly 
distributed over the growing season. The rainfall exceeds the evaporation a 
little. At a first glance this seems a nearly ideal situation. 
However, when the figures over a thirty year period are analysed, a large 
deviation occurs on the side of both low and high precipitation. It seems that 
once in 4 years the annual precipitation is less than 600 mm. On the other hand, 
we see high precipitations of more than 2000 mm once in 10 years and of more 
than 1700 mm once in 5 years. 
Closer examination of the figures shows that in years with high rainfall, the 
excess, about 1000 mm, falls in one month. This 1000 mm in one month can 
be traced as 700-800 mm in a few days. This means that in polder areas crop 
failures will have to be prevented once in 5 years, and that the drainage system 
has to be based on very high - and consequently very expensive - discharge 
requirements. 
Considering further that these low lying polder areas have to discharge into 
a sea with a low tidal range, gravity discharge will be impossible and construc 
tion of a pumping station will be necessary. As a result, the drainage costs will 
be so expensive, that an economical reclamation of these soils, which have a 
high agricultural potentiality, is impossible, despite the favourable first im 
pression.