Observations on flooding in the Calder between Mytholmroyd and Todmorden

Question: 
The December flood seemed, for most of the valley, to be short lived in terms of inundation of towns in the village. Whilst is is obvious that, at the peak of the flood, there was a very large volume of water passing through the valley, this high volume did not seem to last particularly long. It would be useful to know precisely what volumes were passing through various parts of the Calder Valley over the period of, for example, the day before the flood, the day of the flood and the day after the flood. Also, what is the relationship between the amount of rainfall and the volume of water flowing down the river and the height of the water above the river bed - again details to be provided at several points along the river. I appreciate that the impact of rainfall on river levels will depend on the ability of the ground to absorb the rain. That seems, to me, to be the minimum data needed to begin to plan to deal with future events. With information on the relationship between daily rainfall, the amount of water entering the river and the impact on river levels, we will know the volume of water which has to be kept out if the Calder to keep river to an acceptable level. After that, we need to understand where the water is entering the River Calder and to have detailed information on the valleys containing the tributaries. Then, can we begin to work on the individual sources? Up on the moorland areas feeding the tributaries - what can be done by planting of mosses and trees? Can 'leaky dams' be placed in these tributaries? Are there old mill ponds which can be used to store water (can they be restored to be fit for this purpose?) and could they be partially drained when bad weather is forecast but before it arrives, to maximise their storage capacity? Can streams be diverted into these ponds when the water level rises? The same question arises in respect of the canal. Some streams flow into the canal - can others be made to flow into the canal? To avoid the canals flooding if they are to carry this diverted water from the hillside, could the canals be partly drained when heavy rain is forecast and sluices managed during the period of heavy rain to allow this water to flow. At the meeting in Hebden Bridge, dredging seemed to be an unpopular option. I do not understand why but assume it will be considered if it is a way of improving the ability of the river to carry larger volumes of water. Are there areas which could be or are flooded without danger to people or damage to property - and could their ability to hold water be improved? I assume it is possible to collect data on rainfall, time for rainwater to travel from the tops to the river system under different conditions of saturation of the ground and with this information, build models to understand the impact on river levels of individual schemes. How much water is absorbed by different tree species which could live in the Calder catchment area? How much water can be held in a square metre of sphagnum moss - and, would an area of such moss have become saturated by December 2015 because of the heavy rainfall in November? (In other words, do planting strategies deliver one off benefits, or will they always deliver slower throughput of water from the tops to the valley bottom than an environment without such flora?) Overall, to reduce flooding, given that we cannot, locally, control the weather, we can only extend the time it takes for rain to enter the river system, (and, as part of that, increase the amount of water storage available) and reduce the impact on river levels of a given volume of water in the system, by improving flow down the river. I don't know if rainfall levels and patterns are set to change in the future but there needs to be some thought given about what we are trying to achieve. Is 'no flooding anywhere in the Calder Valley under a repeat of 2015 weather' possible? Should we build in a contingency, if is likely that the weather will get worse? If it was a goal, what would need to be done? If the same volume of rainfall which flowed through the valley to cause the floods in December was spread over another day, what difference would that have made to river levels? Looking at the problem from a different perspective, how much water was dropped on the Calder catchment area prior to the flood and what is the rate of flow which could be allowed to avoid any flooding and how would all the individual schemes contribute to that reduction of flow?
Name of Watercourse Referred To: 
Calder
Location of Cause or Solution: 

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Question Reference: 
95
Category: 
Biodiversity
Canal
Catchment-wide
Flood barriers/walls
Natural Flood Management
Peat Bogs and Moorland Management
Research and Modelling
Reservoirs
River flows / Water Levels / Weather
Rivers and Becks
Role of Organisations
Scheme design
Soil / Land Use
Timescales
Trees and Vegetation
Uplands
Asked By: 
Ian
Law
Asker's Location: