**4.4 Stream restoration**

In many instances, pollutant source reductions and built SWM infrastructure may not be enough to recapture watershed integrity because of stream channel alteration. In these instances, restoring stream channels is now a preferred goal. In these designs, hydrology, sediment transport and watershed processes that have fundamentally changed are incorporated into a new channel design [70]. In these designs, streambank stabilization, restoration of the stream channel and reestablishment of riparian vegetation are the areas of focus. To stabilize banks, jetties, tree revetments, rock vanes, rock toes, retaining walls and gravel banks are used [71]. While retaining walls and gravel banks provide good stability they are expensive. Jetties may not provide the same level of protection but are the most cost effective measure and provide a more natural look to the restoration. Tradeoffs exist between appearance, effective stabilization and costs.

To rehabilitate the stream channel, regional curve dimensions, planform pattern, and grade control structures are developed [72]. Grade control structures hold the vertical elevation of the stream constant preventing vertical downcutting. Planform pattern creates an alignment of the stream channel to resemble meanders typical for the regional landscape. Proper channel width and depth are created from a "best-fit" consideration using the bankfull channel dimensions of similar reference stream from within the drainage area.

Unfortunately, there is considerable scientific evidence that instream restoration in USA and Europe has shown very limited success [73–77]. Storm events that exceed bankfull have fundamentally changed restoration design reducing expected performance [78]. Restoration of features (stormwater ponds, riparian vegetation) outside the stream channel have shown some improvement but well under expectations based on investment [79]. Prevention remains the single most effective

**Figure 2.** *Channelized urban river in need of stream restoration.*

restoration technique. Lack of effective measure for restoration may be sensitive to time scales as full recovery may take over 15 years to be realized [80].

The how and where to restore is difficult to decide. Urban land is expensive and the best areas may be privately owned and unwelcoming. Projects are driven by available land to municipalities and public sentiments rather than effectiveness in bringing about the best project restoration outcomes [81]. So because of the expense and limited measured effectiveness restoration projects are currently under debate. It appears that good channel restoration projects are best when integrated into multi management efforts including protection of existing good quality stream sections, reducing stormwater flow, controlling sewage overflows upgrading sewage treatment facilities (**Figure 2**) [82].

#### **4.5 Sediment management**

Managing sediment in urban stream channels may be paramount for improving urban river systems. Sediment moves through these systems in what can be characterized as the "urban sediment cascade" [83]. In this cascade, sediment is generated from two primary sources; first roads and impervious surfaces and then the bed of the aquatic system. As the sediment flows through this urban cascade it mixes with multiple contaminants such as metals [84] and microplastics [85]. This sediment flows from parts of the urban landscape such as street surfaces, pot holes, storm sewers, ditches and docks eventually entering rivers and lakes. This phenomenon makes every storm event a polluting event with the concentration of contaminates dependent upon the storm intensity.

Once in the stream bed this sediment may accumulate for extended periods of time. Evidence suggests movement of sediment fractions larger than the median size of the bed surface material is rare and occurs only at relatively high flows [86]. Such flows may occur once every few years and the movement might not last more than a few hours. This further suggests years of accumulation of contaminated sediment may be severe and pose a possible health risk [87]. Removal of dams as part of an overall restoration strategy to improve fish passage and sediment flow downstream may in actuality be counterproductive toward restoration goals as beneficial evidence of this practice is highly experimental [88, 89]. Prevention or clean up through practices such as street sweeping may be a better management strategy [90].

#### **4.6 Citizen science and education**

The importance of citizen science protecting water quality [91] is becoming more widespread and may be integral to restoring these systems. It bridges the gap between regulators and the public energizing citizens living in urban areas impacted by poor river quality. Citizens can be trained to complete essential tasks, are affordable and can generate good data when verified [92]. Programs such as the The Izaak Walton League's Save Our Streams [93] builds an army of volunteers through training and information to monitor our waterways. This program serves as an intermediary successfully uncovering problems and urging local leaders to take action. These types of programs can even transcend data collection and scientific analysis moving those involved toward a greater sense of place in the watershed [94]. This can further the idea of watershed protection and lead to real policy change.

Education is the other effort underway to secure river protection. Theoretically, an educated public will hold regulators and developers responsible for their actions. Programs such as Global Rivers Environmental Education Network (GREEN)

educates global citizens about water quality problems [95]. Education based curriculum teaching stormwater principles in schools educates future generations about the problems rivers are facing [96]. Such programs are productive. But education is complex. People formulate perceptions about the environment using various levels of experience, normative influences, temporal discrepancies and attitude-behavior measures [97]. Why should people care or why be involved? Answers to these questions are extremely diverse, complex, and poorly understood. The furtherance of educational understanding can only enhance opportunities for improvement.
