Coastal Cutthroat Trout as Sentinels of Lower Mainland Watershed ...

40Unlike flood boxes with sluice type flap gate structures, the majority of flood boxes in theLower Mainland have hinged flapped gates which are designed to respond to thefluctuations in water levels. The style of the flap gate greatly affects the function of thesestructures in regards to fish passage. Flap gates can be constructed of cast iron, steelreinforcedwood, aluminum, or ABS plastic. In addition, flap gates can be side or topmounted. Heavier materials generally require greater head differentials to open. Evenmore important is the location of the hinge, with top mounted gates requiring asignificant amount of force to open beyond a few inches. The apparent inability of topmounted cast iron flap gates to open significantly except during high flow events isbelieved to be the crux of the fish migration problem associated with flood boxes in theLower Mainland (Thomson and Associates 1999).An inventory of these facilities has been undertaken by the Ministry of Environment overthe past decade (Thompson et al. 1999). Many of these facilities represent fish passageconcerns for anadromous salmonids, including cutthroat trout. A report recently draftedby Alan Thomson and Associates summarizes the types of fish passage problems thatresult from different flood box structures. This is based on the results of a monitoringprogram at two different study sites (i.e. unnamed tributary to Serpentine River at 168 thStreet in Surrey and confluence of Drinkwater Creek and Serpentine River in Surrey).Options to address fish migration problems are also provided (Thomson and Associates2005).4.3 Urbanization ImpactsHuman population growth and associated urbanization have had a major impact oncutthroat trout in the Lower Mainland Region, yet documentation of losses is limited. Itis potentially a far greater threat to the conservation of coastal cutthroat trout than bothagriculture and forest harvesting impacts in the Lower Mainland Region. Large-scalelosses of cutthroat production are most evident from a tally of the number of smallstreams that have been historically enclosed by culverts. Of 671 streams present in 1860,approximately 120 streams, many of them salmonid bearing, have been physically lost inthe Lower Fraser Valley (Precision Identification Biological Consultants 1997).Other streams have been converted to ditches, with losses of habitat values fromculverting, and a high proportion of these are within urban areas. A well-known Region2 example is Como Creek in the municipality of Coquitlam. There, a cutthroat-cohostream was largely culverted for >1 km from Como Lake to a low gradient slough-likesection close to the Fraser River. An abundance of sea-run cutthroat in Como Creek hadbeen well known to most young Coquitlam anglers, 50-60 years ago (F. Friesen pers.comm. 2004). Further impacts of urbanization can be expected to occur as the humanpopulation expands further into the Fraser Valley. A significant percentage of streetculverts can be barriers to anadromous fish passage (e.g., Nelson Creek in Coquitlam).Urban streams are frequently channelized, altered hydrologically and intermittentlyreceive releases of harmful pollutants via stormwater drainage systems. They were alsohistorically logged to their banks, thereby losing supplies of large woody debris from the