Editing Battle of Passchendaele (section)

=== Topography ===
[[File:USMA - Third Battle of Ypres.jpg|thumb|{{centre|The progression of the battle and the general disposition of troops}}]]
In Flanders, sands, gravels and [[marl]]s predominate, covered by [[silt]]s in places. The coastal strip is sandy but a short way into the hinterland, the ground rises towards the Vale of Ypres, which before 1914 was a flourishing market garden.{{sfn|Liddle|1997|pp=140–158}} Ypres is {{cvt|20|m|ft|order=flip}} above sea level; Bixschoote {{cvt|4|mi}} to the north is at {{cvt|8.5|m|ft|order=flip}}. To the east the land is at {{cvt|20|–|25|m|ft|order=flip}} for several miles, with the Steenbeek river at {{cvt|15|m|ft|order=flip}} near St Julien. There is a low ridge from Messines, {{cvt|80|m|ft|order=flip}} at its highest point, running north-east past Clapham Junction at the west end of Gheluvelt plateau ({{frac|2|1|2}} miles from Ypres at {{cvt|65|m|ft|order=flip}} and Gheluvelt, above {{cvt|50|m|ft|order=flip}} to Passchendaele, ({{frac|5|1|2}} miles from Ypres at {{cvt|50|m|ft|order=flip}} declining from there to a plain further north. Gradients vary from negligible, to {{nowrap|1:60}} at Hooge and {{nowrap|1:33}} at Zonnebeke.{{sfn|Liddle|1997|p=141}}

Underneath the soil is [[London clay]], sand and silt; according to the [[Commonwealth War Graves Commission]] categories of ''sand'', ''sandy soils'' and ''well-balanced soils'', Messines ridge is well-balanced soil and the ground around Ypres is sandy soil.{{sfn|Liddle|1997|p=142}} The ground is drained by many streams, canals and ditches, which need regular maintenance. Since 1914 much of the drainage had been destroyed, though some parts were restored by land drainage companies from England. The British considered the area drier than [[Loos-en-Gohelle|Loos]], [[Battle of Givenchy|Givenchy]] and Plugstreet Wood further south.{{sfn|Edmonds|1991|p=125}} A study of weather data recorded at Lille, {{cvt|16|mi}} from Ypres from {{nowrap|1867–1916,}} published in 1989, showed that August was more often dry than wet, that there was a trend towards dry autumns (September–November) and that average rainfall in October had decreased since the 1860s.{{sfn|Liddle|1997|pp=147–148}}