The slopes from the Chateau run down to the River Creuse in the south and the River Claise in the north. Once across the Creuse in the south, the land starts to rise little by little, towards the Massif Central. At Tilly, the most southerly village in the Parc, the altitude is 218m.
Water plays a very important role in the Parc, almost entirely originating from precipitation, and present in four main guises:
1. Etangs - shallow (averaging 1.5m deep) stagnant water used for fish farming. These small (average 1-3ha) lakes are not naturally occurring or spring fed. The largest is la Mer Rouge (180ha). They are typical of la Grande Brenne, also known as the 'Land of a Thousand Lakes' (at last count there were in fact 2237 étangs and the number is increasing). The Parc's success, leading to an increase in the number of étangs, many of them privately owned, stocked and managed on a more modern commercial (ie intensive) scale, is not without its problems. Etangs are arranged in series and emptied one into the next, requiring considerable planning to manage when a number are to be emptied into catchment areas in close proximity.
a) The Claise - to the north it is chalk and sand, to the south, clay. The river is greatly controlled with 22 weirs between Luant and Martizay. The flow of water at Martizay in the summer is 100l/second. The Claise flows into the Creuse in Indre-et-Loire (ie outside the Parc).
b) The Creuse - a rather large valley carved out in the Quaternary Era, which today flows across the marine carbonates (limestone) known as the Mid Jurassic Dogger series in the Parisien Basin. The word 'creuse' means 'crease'. The flow in summer at Scoury is 2m³ but is dependent on what is released at Eguzon.
c) The Anglin - upstream the riverbed is a geological coating of igneous* rock, whereas downstream the substrate is limestone, with a flow of 810l/second in summer at Mérigny.
3. Ponds - these are small reservoirs, generally less than 1ha and are typical of the south of the Parc. They have a natural tendency to reduce in size but play a role in collecting and retaining surface water.
4. Springs - there are no springs in most of the Brenne, but in the southern part they are common and often responsible for the creation of wet grassland.
(Note: Much of this information has been cribbed from 'Flore remarquarble du Parc naturel régional de la Brenne' by François Pinet. Any errors are the result of me either misunderstanding or mistranslating the French terminology.)
*The 'Flore remarquarble' actually says 'La partie amont coule sur un revêtement géologique cristallin alors qu'à l'aval le substrat est calcaire,' but I was puzzled by the use of the word 'cristallin'. Many thanks to my geologist contacts for helping with this: Stu, who is English but works in France, taught me the useful phrase 'oui, c'est cristallin ça, je comprend' ('yes, that's crystal clear, I understand') and told me the story of how when the site office at the English end of the Channel Tunnel was jacked up ready to be removed it became clear that about a dozen adders had taken up residence underneath. Apparently you have never seen so many big burly guys scatter so quickly, notwithstanding that they were all wearing full personal protection gear, including safety steel cap toed boots! Thanks also to Hugh (Scottish and working in Scotland) at the British Geological Survey, who put me on to Gaud (French but working in Scotland).