Using surrogates, including scaling issues, in laboratory flumes and basins
The previous chapter outlined the challenges of looking after plants and animals hydraulic experiments. These challenges can be circumvented if inanimate surrogates can be substituted for the prototype organisms without detriment to the relevance of the data collected. Surrogates are partial replicas of biota, mimicking specific organism traits of relevance to the aims and objectives of the study. Physical surrogates range from generalised forms, such as hemispheres or plastic rods, to resin casts that precisely replicate morphology and texture. Some studies have used mechanical analogues that mimic important animal movements. Dead animal shells are regularly used as surrogates for living equivalents. There are a number of practical and research benefits to using surrogates in place of living organisms but also significant limitations. Therefore, it is important that their use is carefully considered. If large-scale processes are being studied then it may be necessary to scale down experiments so that they fit in laboratory facilities. In such studies, scaled surrogates are regularly used. These can be physical surrogates; for example, using cable ties to mimic trees, or scaled biological equivalents; for example, using small plants like alfalfa to mimic floodplain vegetation.