APPENDIX:   FIELD NOTES AND PRELIMINARY OBSERVATIONS 060313:   Sea Wall, Region 4 Observed coastal sediment transport originating in the Amazon and other smaller estuaries in the vicinity. Sluices and pump stations are operated during floods to discharge ponded waters into the sea during periods of low tide. Sea wall is more than 100 years old in various stretches. Riprap appears to be preferred to concrete due to lower cost and perceived better wave dissipation properties. Generally, sea-wall sluices are in various states of disrepair. 060314:   East Demerara Water Conservancy, Region 4 Mr. Bhudu requested a long-boom excavator and a weed cleaner for channel maintenance. He requested additional staff for proper O&M. He stated that another sluice similar to Kofi or Cunha is urgently needed to assure proper flood relief. Backwater raises the stage in the upstream portions of the conservancy by 0.5 ft. Mr. Bhudu is of the opinion that a network of conveyance channels are needed in the conservancy to facilitate drainage during floods. The Enmore-Shank dam stretch is the weakest link in the system. This is where the crest width is the narrowest. Time of travel from Flagstaff to Five Gates sluice is 2 hours (by boat). Question: What about sluice relief when Demerara river is at flood stage? Mr. Bhudu states that they resort to mobile pumps if faced with high tailwater level. Cunha sluice has been rerouted due to construction of the Barana wood mill. This is effectively acting to reduce conveyance. 060315:   Mahaica-Mahaicony-Abari, Region 5 Need for flood control and erosion control is apparent. Much sediment in Mahaica river near road intersection; appears localized; need to look for nearby sources. Dredging of the river mouth is not justified in view of lack of data and other uncertainties. Experience shows that dredge pits are filled within a short time after dredging. Emphazise needs for data collection to support modeling, design, forecasting, and operation: network of raingages and stream gages. 060316:   Georgetown, Region 4 Guyana lacks a comprehensive disaster management plan. Mr. H. George stated that what is needed is to drain the water off the land quickly (more flood relief?) According to sea defense staff, the sediment along the coast of Guyana originates in the Amazon's mouth. 060317:   Boereserie Water Conservancy (BWC), Region 3 Need to dredge channel between Naamryck sluice and 8,000-ft weir. The channel width has been reduced by 60% due to vegetation encroachment. Clearing is needed. The Waramia relief sluice discharges into the Bonasika river. It has five gates, each 16-ft wide, with total discharge of 2,000 cusecs. Geographical coordinates at N 06o 40' 10.1' W 58o 28' 57.0" Geographical coordinates of 8000-ft weir: begin N 06o 42' 39.0' W 58o 28' 19.0"; end N 06o 41' 27.7' W 58o 28' 52.6" . Mr. Kamaludeen stated the need to raise the dam crest to 62.8 ft G.D. It is currently at 61.7 ft G.D. for a 6-mile distance, from T-dam to Naamryck. He stated the need to clean/desilt the High Dam waterway for about 27 miles, from Zeeligt to the Waramia sluice. Current dimensions are 16-18 ft wide by 8-9 ft deep; it should be 40 ft wide by 14 ft deep. Every year five gates (Waramia sluice ?) are opened, in December and July, to release flood waters. It takes three weeks for the signal to travel from Waramia sluice to Northeast corner of High Dam (?). Mr. Kamaludeen suggests augmenting the storage capacity of an otherwise shallow lake with a network of storage channels, which may double as conveyance channels during floods. 060317:   East Demerara Water Conservancy (EDWC), Region 4 Raise weak section of EDWC for 10 miles, from Flagstaff to Anandale. Crest should be 59 ft G.D., it is 57.5 ft G.D. in some places. Width at base of dam should be about 48-64 ft. Need to habilitate conveyance channels to help flood waters flow in the direction of the relief sluices during flood. According to Mr. Bhudu, a network of 3 NS × 3 EW = 9 total channels is needed. The channels should be 100 ft wide by 25 ft deep. Two new sluices to the Demerara river are needed. Sluices to the ocean are impractical due to people settlement and tide influence. Need to straighten the Cunha sluice. Furnish mobile pumps in case sluices are unable to discharge to Demerera due to high tailwater levels during floods. Mr. Budhu observed that water in the channels (turbulent flow) in the conservancy moves about 80 times faster than the water in the overland flow (mixed laminar-turbulent). Two new sluices can be implemented in the vicinity of the existing Land of Canaan (Five Gates) sluice. Mr. Bhudu recommends a staff increase from 40 to 75 persons to handle increased O&M tasks. 060317:   General observations, Regions 3 and 4 Repair/rehabilitate portions of dams in the East Demerara and Boireserie conservancies. Study the hydrology and hydraulics of the flow in the conservancies, subject to floods, tides, surges, and climate change. The latter includes changes in rainfall patterns (more intense rainfall) and sea-level rise due to global warming. In particular, determine whether the system(s) needs additional sluice and/or weir capacity to guarantee the integrity of the conservancies into the future. Built capacity to cope with floods by supplying equipment needed to desilt and maintain/repair conveyance channels to sluices. Built capacity to operate the system in extreme emergency situations by supplying mobile pumps, boats, and personnel. Built capacity to gather hydrologic data for real-time forecasting, even if response time is short. This will reduce the need for sluice relief. There is a need for building a network of conveyance channels which would double as storage channels, and viceversa. Study strength of soil used to build the dam (combination of pegase and clay), with aim at design of the dam repairs. Determine the location of up to two new sluices in EDWC. Staff gage the Demerara river along the sluice locations. Determine if a weir is needed in EDWC, and if so, what would be its size and where would it be located. Study operational alternatives to structures, i.e., a combination of controlled releases immediately prior to or at the beginning of the two flood seasons (December and July). The releases would be based on event forecasting. Choose appropriate design flood and frequency. Use a freeboard hydrograph for the extreme case. Develop capacity to construct conveyance channels in conservancies to drain flood waters quickly (compare the speed of mixed laminar-turbulent vs turbulent flow). Clear the vegetation growth in the proximity of 8,000-ft weir in the Boireserie Conservancy to enable unimpeded flow. Set up a periodic vegetation clearing program, as needed. Check freeboard in Boireserie Water Conservancy dam to assess need to raise the crest, for either flood control or water supply. Go back to Mission Report

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