GEOGRAPHY’S CONTRIBUTION 209 
itself (and every year cease to flow for months on end), whereas 
the majority of large storage reservoirs established in the arid 
lands with which a parallel is drawn impound waters of rivers 
rising in rainy or even snow-covered country. The upper Rio 
Grande furnishes an opportune example. Although its basin is a 
typical arid zone watershed, the river rises among the snow-clad 
peaks of Colorado and is fed by mountain streams. 
That reservoirs in the Nordeste have produced even punier 
results than could be expected (with around 2,000 hectares or less 
than 5,000 acres under irrigation in 1950) is due essentially to (1) 
lack of research regarding the multiple factors involved in the 
establishment of reservoirs and (2) failure to utilize even what 
irrigation potential has been obtained—most agricultural activity 
having to do with reservoirs is carried out in the storage basin 
itself, where the drop of the water level exposes moist land. How- 
ever, these are matters for the hydraulic and irrigation engineers. 
The point I want to make here may be a rather surprising one. 
But a survey of the existing official literature on the Nordeste and 
discussions with professionals responsible for public policy have 
led me to conclude that a large part of the opposition to a realistic 
appraisal of the remedial measures for the Nordeste stems from 
an erroneous interpretation of the landforms in this area. One of 
the outstanding features of the region is the large number of 
gorges carved through ranges scattered throughout the sertao 
(Figure 6). The general belief is that almost all these water gaps 
are the result of erosion by the outlets of lakes where waterfalls 
poured over the impounding ranges (14). Some interpretations are 
hazy as to the origin of these hypothetical lake basins. Others 
attribute them to crustal movements; at least one lake is ascribed 
to an upwarping during the Caledonian revolution (which took 
place some 300 million years ago) (1). All such interpretations 
lend comfort to the notion that “it is enough to rebuild the 
ranges, breached by erosion, in order to detain the rivers which 
escape through these gaps” (2). Once the mountain ranges have 
been patched up, man will have reestablished the lakes (which 
became extinct by the progressive cutting down of their outlets), 
thus providing large volume reservoir storage and even exerting 
