Following on from the geophysical fieldwork conducted on the 27th and 28th July 2015 (microgravity), further investigation into the possibility of:
- brine influx from any “leak” through to nearby mines
- changes in depth in the canal due to subsidence
Day 1: 10th September: Depth & Temperature
The depth of the canal and temperature of the water is to be tested
Testing the Hand held sonar device
20 depth measurements conducted at random intervals (stationary) alongside the Marston Canal, from the towpath prior to research being undertaken. Measurements and observations to be compared with a 3m long stick with measuring tape glued and varnished to it.
Equipment: Norcross H22PX handheld Digital Depth Sounder Description:
The Norcross depth sounder is a handheld depth sounder, fish finder and temperature gauge in one. The Norcross 2200PX is the most versatile handheld depth sounder ever produced. The depth sounder works in the water, under water and when pressed against the hull of your boat. Not only will it give you instant depth readings, from 70cm to 61m in 10cm precision but at the press of a button the display will give real-time temperature (water or air) and fish readings. Depth Sounder Use it as a portable depth sounder or as a backup depth sounder on your boat. Use it in the summer as a range finder and temperature meter while diving. No matter how you use it, the DF2200PX is a piece of equipment you should never leave without.
Fish Finder: There is no guessing where the ledges are or where the fish are hiding, when you use the DF2200PX. The press of a button allows you to scan an area for drop-offs, ledges, or hiding fish within 60m. Features Depth readings from 70cm to 61 m Waterproof to 61m depths for Diving Reads in feet and metres Waterproof, maintenance free button Instant depth readings, 4 times per second to the nearest 10cm 4 x ‘AA’ batteries with 30 hours of continuous use Water or air temperature Fish indicator pinpoints hiding fish Manual mode gives one touch readings ShootThruTM technology allows readings through ice or boat hulls Floats.
|Reading #||Depth with Measuring Stick (m)||Depth with Sonar (m)||Notes|
|1||1.34||1.3||Hard base, little-no Sediment|
|2||1.38||1.3||Hard base, little-no Sediment|
|3||1.20||1.2||Hard base, little-no Sediment|
|4||1.07||0.9||Soft Base – sediment build up|
|5||0.90||0.8||Soft Base – sediment build up|
|6||0.93||0.8||Soft Base – sediment build up|
|7||0.91||0.8||Soft Base – sediment build up|
|8||0.91||0.9||Hard base, little-no Sediment|
|9||0.90||0.8||Soft Base – sediment build up|
|10||1.05||0.9||Soft Base – sediment build up|
|11||0.80||0.8||Hard base, little-no Sediment|
|12||0.75||N/A||Too shallow for reading|
|13||1.41||1.1||Soft Base – sediment build up|
|14||1.01||0.9||Soft Base – sediment build up|
|15||1.20||1.2||Hard base, little-no Sediment|
|16||1.29||1.2||Soft Base – sediment build up|
|17||1.12||1.0||Soft Base – sediment build up|
|18||1.29||1.2||Soft Base – sediment build up|
|19||1.25||1.2||Hard base, little-no Sediment|
|20||1.29||1.2||Soft Base – sediment build up|
The test shows the reliability of the sonar – which measures depth to the sediment NOT the solid – floor of the canal. Despite an accuracy of 0.1m, I feel that measurements taken with rope and weight, or even a stick, would be equally inaccurate, if not more so, due to the boat movements. However, should there be an area with deep silt before hitting the bottom, this could be relevant. Therefore, I intend to verify 10% of stations with a stick.
- 3 readings (depth and water temperature) to be taken at each position using : Norcross H22PX handheld Digital Depth Sounder
- Notes to be made on proximity of rain / weather changes.
- Reliability:~10% of survey stations to be checked with stick
- Stick: notes to be made on “softness” / presence of silt on the canal floor – pushing it down till it reaches the hard base.
Station markers on the side of the towpath used in fieldwork on 27th and 28th July 2015: readings taken (roughly) in the centre of the canal off the side of a boat. 1 person walked alongside the canal to alert of station and to ensure that we took readings in roughly the correct position (canal path often not visible due to boats tied to the towpath).
Thoughts / observations after the fieldwork
- Frequency of stick measurements was increased after a reading where it did not reach the bottom. I am intrigued by the depth reading recorded (stick) of >2.87m depth at station 30 (and 2.3m at station 40) and would like to explore this further – especially as the canal claims to have a depth of 5ft 6 inches (1.68m) throughout.
- We were lucky with the weather: sunny and light breeze all day. (Air) Temperatures reached 20°C in the sun. Although at some points the breeze caused slight drift in places, and the (light-weight, river) boat needed repositioning.
- I feel that the temperatures were only varied due to periods of light cloud cover / shadows. More notes on this would be advisable should this fieldwork be repeated, although given the time allowed, and the fact that we often had to halt fieldwork due to heavy traffic, I am not sure how useful such readings are.
Day 2: 11th September – Conductivity Testing & Temperature
The salinity of the water is to be tested with a portable multi-parameter instrument (WTW MultiLine P4 SET, Weilheim, Germany).
- 3 readings to be taken at each station using the WTW MultiLine P4.
- 20 seconds per reading
- Rinsing of the equipment using Base Station water (CW9 7NB Tap water) and dried with a microfiber cloth between each station.
- Reliability: 10% of survey stations to be revisited and re surveyed
- Notes to be made on proximity of boats / rain / weather changes.
Station markers on the side of the towpath used in fieldwork on 27th and 28th July 2015.
Thoughts / Observations after the fieldwork
- We were lucky with the weather again: sunny and light breeze all day. (Air) Temperatures reached 20°C in the sun.
- I feel that the temperatures were only varied due to periods of light cloud cover / shadows.
- Salinity (Sal.) readings: All < 0.5 ppt, which is indicative of freshwater salinity. Tap water (base readings) was 0.0. Canal water was 0.1 consistently throughout.
- Conductivity: ~770 µS/cm (on average). Initially, we surveyed stations 1-11 on the 10th, whilst waiting for the boat to arrive. However, when we returned on the 11th, the conductivity readings were very different (~758 µS/cm (on average)) so all readings were repeated.