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such surveys to find the balance between the scientific and the practical side of the work. Research is, of course, necessary to obtain satisfactory practical results, but the scientific programme should not grow beyond proportion as far as time and budget are concerned. The same practical attitude also influences the Outlook of the finished map: most maps will be in black and white, and the map symbols will be chosen from what is commercially available. The ‘stick up’ method, using Zipatone, and the like, is freąuently used. This sets rigid limits to the application of (coloured) map symbols as used for the regular geomorphological map series of Poland and other countries. It is certain, however, that once a symbol comes in generał use, it will also become manufactured.

Increasing emphasis is laid on the water resources of development areas. A number of factors play a role in this connection, but they all center on the water balance: precipitation = run off 4- infiltration -f evaporation. The necessary hydrological data are often not or insuffi-ciently available, which forces the hydrologist to leave the well trodden paths and to look for unconventional methods which will at least give him an adeąuate idea of the order of magnitude of the various aspects of the water problem. Aerial survey and especially photo geomorphology is then considered. Aerial photographs aid in selecting representative sites for rain gauges, especially in mountainous terrain. Every part of the drainage basin then is classified according to exposure, elevation, etc. Several gauges should be placed in every class distinguished and this rainfall data combined with the area covered by each class will give a fairly good idea of the annual rainfall and its distribution. The deple-tion of a snów cover can also be studied from the air, provided that successive coverages of aerial photographs are available. Interception of precipitation by the vegetation can be roughly estimated from the canopy density, etc., but little can be done about the evaporation. The surficial run off depends largely upon the permeability of the rock and soil types occurring and on the morphological characteristics. The drainage density and the steepness of the slopes are indications for its importance, and geomorphological airphoto interpretation is therefore an adeąuate approach. Springs can often be located from the air, especially if a pro-longed dry season occurs and if infra-red photography is used. Dam site selection is also speeded up considerably by the use of airphotos.

Other possible applications of aerial photograph interpretation are e.g. in studies on disastrous floods, like the work of T. Nakano in Japan, and in irrigation studies. The remarkable thing in the latter pro-jects is that the desired vertical accuracy is many times greater than the necessary planimetrie precision. W. Schermerhorn (1958), the Dean of the ITC, Delft, therefore suggested a combination of the slotted template map compilation with an accurate leveling. The results of the leveling are indicated on a photomosaic where after the contours are completed while taking the landforms into consideration. Quite feasible are studies on the prevention or diminuation of the filling up of reser-voirs. The areas where rock types outerop which are particularly suscep-tible to accelerated erosion, can be delineated and so can the steeper slopes. The necessary soil conservation and land use devices can thus be indicated and localized. The possibilities were explored at the ITC from an example from Ceylon.

Groundwater studies with the aid of aerial photograph interpretation are often carried out along the following lines: Analyses are madę — on

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