8/4/1998 WATERWAYS COMMISSION Minutes

Home Browse Search

g r Mashpee River Dredging Project Channel Alternatives 5 July 1998 The purpose of this paper is to prepare the Waterways omission to discuss the alternatives for dredged channels in the Mashpee River at our next meeting, and to make a recommendation to the Board of Selectmen on the extent of dyed in we should seek to . g penmt, There are several alternatives for configuring the channel to be dredged in the Mashpee River. The assumption used for the Aubrey Consulting, Inc. hydrodynamic modeling is a channel 3 feet deep at mean low water(nominally 4.9 feet at mean high g water), and 50 feet wide (average). If we stick to these dimensions, we can demonstrate that there will be no negative impact on the river's water quality. If we change these assumptions, we would probably need further modeling of the new scenarios. Question-to Do we agree on these assumptions? Five segments were postulated for the modeling as shown in Table 1; Tab] 1 e m nts Iii tanc andubic YgLds of Material en Location Distance Cubic Yard A Fopponesset channel to Godfrey Road 1200 feet 5 360 B Godfrey Road to Stenberg Parcel 1100 feet 31260 tenberg Parcel to Orsini Beach Narrows I 100 feet 2}241 D Orsini Beach to South of Amos Landing 2000 feet 92415 South of Amos Landing to Canaways Cove 2700 feet 16,734 Cubic`'dards are charted in Figure 1. Bob Hamilton did not calculate volumes for segments D and E. My calculated volumes are based on the design dred e de thft g p MLw) averaged with the 1 foot over-dredge allowed for pay purposes, and seem to agree' reasonably well with Bob's calculations. The radona.le behind breaking the river into segments was to see the accumulative effects in residence tunes as you go upstream. That doesn't need to apply anymore if we are dredging for navigation purposes. Clearly, Segment A is the mouth of the river, is the most important segment, and would be dredged first. The second segment,is also important because a fair number of boats are moored there. Segment O is less important because it already has a fairly deep channel, but is also less expensive to dredge because it . � g has less material to remove. It also connects to the naturally deep channel at the narrows just above Orsini Beach. Segment D has only a few moored and docked boats in it but is extremely shallow, so people are limited in the times they can navigate that part. There are no does or moorings upstream ftorn Al wickets property, which is about half way up Segment D. f Y