CRAB and MIT Sea Grant Chart of the Charles River

The Charles River in Massachusetts is an urban river that is also one of the most active recreational rivers in the country. Unfortunately, sediment deposition has been a long standing problem in the Charles River. It was recently highlighted in articles published by the Boston Globe in 2011 and WGBH in 2016. In recent years, sediment deposits have caused several incidents that have resulted in damage to watercraft and personal injury. While the sediment appears to be a larger problem where major tributaries - Laundry Brook, Hyde Brook, Faneuil Brook, Muddy River, Stony Brook - empty into the Charles, once the sediment is in the river, it can spread to other areas, causing further problems especially where it is already shallow. This problem is not limited to the areas upstream of the BU Bridge. A significant bar upriver of the Massachusetts Avenue Bridge is shallow enough and large enough to be a navigation hazard to both sailboats and motorboats. There are also the extraordinary events such as the water main breaks in Weston in May 2010 and near the Anderson Bridge in August 2015, both of which caused large amounts of sediment to be moved.

It has been difficult to marshal the resources to remediate areas impacted by sedimentation since much of the knowledge about the shallows and bars has been anecdotal, coming from the daily experiences of the boaters on the river but not backed up by quantitative data. To address this issue, the Charles River Alliance of Boaters (CRAB) has developed a partnership with the MIT Sea Grant College Program to create a chart of the river depth between Science Park and the Watertown Dam, and to monitor changes in the river bottom in the future. Based upon some feasibility studies done in late 2015, more detailed and extensive measurements were undertaken in 2016. To date, most of the river between Newton Yacht Club and the New Charles River Dam has been surveyed for depth (see image below) and relative hardness of the river bottom. In the summer of 2017, we plan to complete measuring these remaining sections, as well as do more detailed measurements near the bridges.

The initial scope of the project is described below:

1. Depth Measurements:
   Inexpensive fish-finders have been used to record the depth, as well as the time and GPS position of each sonar reading. While the depth is measured by the delay in the sonar echo, the relative hardness of the river bottom can be inferred from the strength of the sonar echo. The section of river between the BU Bridge and Community Rowing has been measured by driving sonar tracks at various distances from the shoreline on trips to retrieve data from the depth data loggers (see below). The section of the river downriver of the BU Bridge has been measured by driving a patterned grid on the watersheet.
   
   
2. Influence of Daily Water Releases:
   As part of flood control measures, water from the river is released into Boston Harbor at low tide and held in the river at high tide, slowly accumulating. This causes the water level in the river to change over several inches during the course of a day. A gauge at the First Street Bridge in Cambridge records the variation in the height of the watersheet. While this gauge is a good measure of the watersheet downstream of the BU Bridge, there are no gauges further upriver and the variation in the height of the watersheet is not well understood.
   We have installed three depth gauges and data loggers at the Riverside Boat Club, Herter Park, and Community Rowing. These additional gauges have provided insight into how the height of the watersheet varies along the length of the river. Due to the lack of rainfall over the 2016 summer, the section of the river below the Watertown Dam has acted as a lake with the height of the watersheet varying almost uniformly along it entire length. If there had been more rainfall, it was expected that the height of the watersheet would have been different along the length of the river. We plan to keep the additional gauges installed for a few years and will continue to monitor how the height of the watersheet changes during periods of significant rainfall.
   In order to more accurately determine the depth of the river, all raw depth measurements have been adjusted to account for the variation in the height of the watersheet.
   
   
3. Development of Digital Charts:
   The sonar data gathered in the field was processed using ReefMaster PRO software to generate two-dimensional contours of both depth and relative hardness that were then exported via kmz files. To enable the public to access this data, the following formats have been developed:
   • Chart Booklet: A printable PDF file that includes an overview of the river from Watertown to Boston Harbor, and more detailed charts of each section of the river. Separate booklets for water depth and river bottom hardness would be available.
     
   • Large Format Overview: Similar to the map developed by the Charles River Conservancy showing the parkland surrounding the river, this would include an overview of the river showing the depth of the river bottom. This would be suitable to be posted on the wall in every boathouse.
     
   • Google Map and Google Earth: On-line versions of the depth and relative hardness data using both Google Maps and Google Earth.
     
   • ArcGIS: ArcGIS is a geographic information system (GIS) that provides an infrastructure for making layered maps openly available on the Web.