The Hazel Brook, also known as the Hen, is a tributary of the River Trym

River Trym

The River Trym is a short river, some in length, which rises in Filton, South Gloucestershire, England. The upper reaches are culverted, some underground, through mostly urban landscapes, but once it emerges into the open it flows through a nature reserve and city parks before joining the tidal...

 in Bristol

Bristol

Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. It rises at Cribbs Causeway

Cribbs Causeway

Cribbs Causeway is a road in South Gloucestershire, England, just north of Bristol, which has given its name to a large out-of-town shopping centre, including retail parks and an enclosed shopping centre known as The Mall...

 in South Gloucestershire

South Gloucestershire

South Gloucestershire is a unitary district in the ceremonial county of Gloucestershire, in South West England.-History:The district was created in 1996, when the county of Avon was abolished, by the merger of former area of the districts of Kingswood and Northavon...

. From there, its course takes it south, passing the western end of Filton Aerodrome on its left bank, through Brentry

Brentry

Brentry is a suburb of north Bristol, England, between Henbury and Southmead which is spread along the southern edge of the Avonmouth-London railway line....

 and Henbury

Henbury

Henbury is a suburb of Bristol, England, approximately 5 mi northwest of the city centre. It was formerly a village in Gloucestershire and is now bordered by Westbury-on-Trym to the south; Brentry to the east and the Blaise Castle estate Blaise Hamlet and Lawrence Weston to the west...

 before dropping through a steep limestone gorge in the Blaise Castle

Blaise Castle

Blaise Castle is an 18th century mansion house and estate near Henbury in Bristol , England. Blaise Castle was immortalised by being described as "the finest place in England" in Jane Austen's novel Northanger Abbey....

 estate. It continues south through two lakes before joining the Trym at Coombe Dingle.

Hydrology

Surface run-off in the upper catchment of the Hazel Brook, especially from the large retail centre at Cribbs Causeway

Cribbs Causeway

Cribbs Causeway is a road in South Gloucestershire, England, just north of Bristol, which has given its name to a large out-of-town shopping centre, including retail parks and an enclosed shopping centre known as The Mall...

, sends a good deal of silt into the system, slowing the flow and creating a risk of flooding downstream in the Trym. This problem has now been partially alleviated by the construction of the Catbrain

Catbrain

Catbrain Hill, simply known as Catbrain, is a small village near the north of Bristol, at the edge of neighbouring district South Gloucestershire, England. It is located by Cribbs Causeway, on a road that contains many car dealerships....

attenuation reservoir near Cribbs Causeway. Measurements of pollution by the city council show the water to be relatively clean.