Sunday, 19 May 2013

Temperamental Mole

Ecological consultant Rebecca, taking water samples under the netted section of the River Mole

A tributary of the River Thames, the River Mole rises just south of Rusper village in West Sussex, flowing north-west for 50 miles (80km) before reaching the Thames at the north Surrey border.



At Gatwick our section of the River Mole is rather open and slow-flowing, passing under the airfield through a tunnel and exiting on the north side. At the southern point where it enters, a Kingfisher is regularly spotted zipping in and out.
   The course of the Mole has been altered several times since the airport began operating commercially in 1945. During a massive flood alleviation project in 1999 it was diverted once more from its course north of the airfield; now it travels west for 400m parallel to the taxiway before meandering in a north-easterly direction. With a good diversity of riffle formations, pool sequences, backwaters, lush wet grassland and reedbeds, it is in my opinion quite a lovely and natural-looking section of river.

The River Mole on Gatwick's Landholdings, north of the airfield

Vantage point from the grassy mound, overlooking the airfield - NWZ

Reedbeds in winter

The water level at Povey Cross has reached level 2 (my cunning theory is that the numbers represent 10cm, putting the water level at 1.2m.) In the past I have seen the water close to over-topping the stick.

Much of the catchment area of the Mole lies on impermeable rock, meaning that the water level responds extremely rapidly to heavy rainfall. My first week of surveying at Gatwick taught me a punitive lesson… a few of my reptile mats have probably washed up somewhere in Surrey.

Rebecca kicking the silt and netting the river-dwelling invertebrates

The water quality of the river can also fluctuate greatly depending on the season. The ecologists Rebecca and Victoria from Penny Anderson Associates regularly carry out aquatic invertebrate 'kick surveys', taking samples back to the lab for species identification under the microscope. Identifying the flora and fauna occurring in the waterways is particularly useful, as certain species are very sensitive to pollution and could act as indicators of any negative impacts of the airport's operations. On Monday they visited Gatwick and I was able to join in to see how it is done.

Damselfly nymph covered in silt - possibly a Banded Demoiselle?


Common Backswimmer (Notonecta glauca)


Diving beetle species


A small leech


Freshwater Shrimp (Gammarus pulex) is a type of amphipod crustacean

An Orb Mussel, a type of freshwater mollusc

I particularly enjoy this time of year when the Reed Warblers set up their territories all along the Mole. If you happen to wander west along the public right of way from Povey Cross you can hear their repetitive, mechanical sounding song...

I took this photo of a Reed Warbler along the Mole last summer -
 possibly my best birding photo so far!

And finally, one of the mystery coconuts which wash up regularly along the River Mole... No explanations have sufficed so far, but it gives me a hankering for lime and a tiny little umbrella.