Issues with the River Ver and Lake

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The River Ver is a chalk stream and a tributary of the River Colne in Hertfordshire. Chalk streams are an internationally rare habitat. There are only around 200 worldwide, most of which are in southern England. Chalk streams are defined as watercourses that get most of their flow from chalk-fed groundwater. They should also show the classic chalk stream characteristics of crystal clear water flowing over a clean gravel bed. As their flow comes predominantly from chalk aquifers, they should have stable temperature, pH and flows which rise and fall slowly, reflecting the level of the groundwater.

The River Ver has been historically altered for e.g. milling, flood risk, amenity and recreation. These alterations include:

River Ver

Impoundments
Restrict fish passage
Loss of bed gradient
Excessive bed siltation upstream
Loss of natural habitat and flow diversity upstream

Hard engineering (e.g. concrete banks) 
limits the ecology and habitats

Over-wide and straight channel
Lack of flow diversity
Lack of habitat diversity
Excessive bed siltation
Reduced resilience to climatic changes

Realignment of river channel 
Perched channel (the river is at a higher level than the valley bottom) resulting in disconnection from the groundwater table which is very important for a chalk stream.
Loss/disruption of bed gradient
Disconnection from flood plain
Reduced resilience to climatic changes

Dredging 
Reduced channel habitat and flow diversity
Dredging bunds along the channel restrict floodplain connectivity

Increased groundwater abstraction
Reduces river flows
Increases frequency of low flows/channel drying
Limits river ecology, especially in combination with the other alterations listed

Flow splits (e.g. to feed lakes, or multiple channels for historic mill industry)
Results in lower flows in river channel
Reduced resilience to climatic changes
Limits river ecology, especially in combination with the other alterations listed

Such alterations limit the form and processes that create and sustain the habitat to support the ecology within the river. The result is that most of the River Ver through St Albans has lost its chalk stream characteristics and is in a poor condition. 

Below are two photographs, the first shows the poor quality of the River Ver through Verulamium Park with silty bed, hard banks, no vegetation and an overly wide channel. The second shows the Ver near Sopwell House which shows a much more representative image of a chalk stream with clean gravel bed suitable for fish to spawn, lush marginal and in-channel vegetation such as the iconic chalk stream plant water crowfoot and natural banks gently sloping down to the water
Ver river project website image 3  Ver river project website image 4

Issues with Verulamium Park lakes

The lakes in Verulamium Park were constructed between 1929 and 1932 partly to give much needed work to the unemployed during the depression. The lakes were lined with hand poured concrete and are no more than about 1m deep. Some of the issues with the lakes are:

Low throughput of flow
The lakes are fed by the River Ver via a sluice gate into the northern boating lake. The volume of the lakes is comparatively very large to the amount of flow they receive from the River Ver. As we mentioned above, the river itself suffers from low flows and often doesn’t have water to spare for the lakes. When the river level is too low, no water enters the lake. 

Eutrophication – the lake is too nutrient rich. Causes of this are:
River water (which feeds the lakes) is naturally more nutrient rich that lake water should be
Feeding waterfowl - uneaten food rots in the lake
Excessive waterfowl numbers (attracted by feeding) - droppings are a significant source of nutrients
Leaf litter – prevailing winds in the park blow huge amounts of leaf litter into the lake
Bottom feeding fish e.g. carp – these stir up the silt on the bed of the lake and increase water turbidity and release stored nutrients into the water. Their faecal waste is also a nutrient source.

Excessive sedimentation
More organic material enter the lakes than can be naturally processed by the lakes (see eutrophication). This builds up as silt on the lake bed.
When the water level is low sediment protrudes above the surface. This represents a hazard to wildlife, people and dogs who walk onto it and can be malodourous in warm weather.

Lack of aquatic plants which would uptake nutrients and provide habitat to invertebrates which would also remove nutrients from the lake. Reasons include:
Grazing wildfowl and fish eat young plants so it’s difficult for them to establish
Plants can’t root into the concrete bed
Sheer concrete bank excludes natural marginal plants
High turbidity and low oxygen conditions also restrict aquatic plant growth

Shallow, even depth 
The lakes have a high surface area to volume ratio making them more susceptible to dramatic water temperature increases in summer. This can create conditions which cause algal blooms and oxygen crashes.

Avian botulism outbreaks 
Botulism bacterial spores are naturally occurring and can survive for years. However, the bacteria only produce toxins under particular environmental conditions, which are generally believed to include warm temperatures, anoxic conditions and an organic nutrient source.Poor water quality (water quality analysis is being carried out to provide more detail on this)

Potentially contaminated silt
Silt analysis is being carried out to provide more detail on this

Date of last review: 24 November 2017