The Mimram Valley is named after the River Mimram, which rises from a spring to the north-west of Whitwell, in North Hertfordshire, England, and makes its confluence with the River Lea near Horn's Mill in Hertford. At Whitwell there are watercress beds which have existed since Roman times and these are fed by the same springs. The valley extends northwards where it becomes known as Lilley Bottom. Other sections of the valley are known as Kimpton Bottom and Codicote Bottom.
Although a dry valley to the north, it has been known in particularly wet years for the River Mimram to be extended for several miles by springs in the upper valley. In 2001, in a neighbouring valley to the west a village was flooded. The Valley is the furthest east of all the Chiltern Hills valleys.
The river is the subject (and speaker) of a Stevie Smith poem, The River God. Popular and enjoyable though this poem has been for its many readers, the description of the river in the poem bears little relation to the geography of the actual Mimram.
Yeh Duniya Hi Jannat Thi
Yeh Duniya Hi Jannat Hai
Yeh Duniya Hi Jannat Thi
Yeh Duniya Hi Jannat Hai
Sab Kuch Kho Kar Aaj Yeh Hum Par
Bheed Khula Hai Seene Mein