**1. Introduction - how did we get here?**

Urban environments including our buildings, roads, traffic, residences, industries, sewage treatment systems, population centers, parks and precipitation patterns all intertwine creating observed water quality in these communities. Water resources and the people living in and around them are intricately linked whether we understand this or not. The observed impact is now so pervasive scientists have suggested a new epoch beginning in the 1950s as the Anthropocene. Regardless of the label, this current age of human influence on the environment is very pervasive creating many stressors that plague water quality. Excessive sediment and erosion mixed with microplastics, pathogens, toxics and nutrients flow through our urban rivers daily. In order to improve this condition, we must first understand the origins.

Our rivers were not always degraded. Nature exists in a state of dynamic equilibrium with our surroundings. Rivers are no different. The river is in equilibrium with its drainage area. Historically, precipitation struck vegetation directly infiltrating into the ground as it was not covered by development. Entire watersheds were vegetated and these are the conditions rivers and streams equilibrated into. Precipitation flowed into the river but mainly through the surrounding soil first. The watershed stored precipitation in the ground, purified it as it slowly migrated toward the stream then released it through lateral discharge into our rivers. Any

precipitation flowing over land only occurred during large storms and this input was periodic. Thus, the size and shape of streams and rivers reflected this pattern. The river system sometimes flooded but not as a catastrophic event. It flowed into the floodplain adjacent to its banks where essential nutrients and replenishing sediments sustained the river system. Rivers created a mosaic of serpentine meanders from mountain headwaters to the coast gently changing while moving sediment from one bank to another. It was a river in harmony with its surroundings.

But floodplains are flat and the alluvial soil desirable. Building projects need flat land for development and farmers need good soil for crops. These floodplains became premium resources early in our history before we learned to flatten plots of land for our buildings and fertilize soil for our crops. We developed floodplains around major rivers that soon became urban centers. Development moved up the water course fanning throughout the drainage basin. Rivers were our first highways, so commerce easily moved along these waterways and development prospered at major ports.

Precipitation contacting these built impervious surfaces instantaneously generated a new pattern of water flow. Water that previously traveled through groundwater now flowed as surface runoff. A river once in harmony with its surroundings and dependent on groundwater (a term called hyporheic flow) now became a conveyance for surface water discharge. In response, the river eroded to gain harmony with this *new* pattern of flow. Development increased, engineers designed more conveyances, pipes, levees and floodplain relevation to alleviate flooding and remove water quickly from our built surfaces. Now contaminated and not purified, surface water became the predominate input into our rivers. More built environments created ever increasing discharge resulting in dangerous flooding. To contain this problem, retaining walls were built. River erosion multiplied as construction continued throughout the watershed. As this intensified, encasement of the river into pipes and culverts became the standard of management. What was once a majestic river flowing through a beautiful landscape naturally purifying itself was transformed into an artificial conveyance filled with polluted water.

### **1.1 The paradox of development**

Our social evolution further exacerbated this problem. The built environment is expensive and with the advent of indoor plumbing an extensive system of water movement became necessary. These pipelines were built under the construction then along the river banks impacting its natural flow. Large scale purification plants appeared at the river mouths. The extensive urban network required rapid and efficient movement of water away from surfaces so extensive systems of stormwater drainage began to appear. Environmental regulation multiplied requiring more and more infrastructure with development. The landscape became an intricate stormwater and sewage drainage network littered with culverts, sedimentation ponds, curb and gutter and isolated streams only noticeable over bridge crossings.

To pay for this, urban governments taxed the land that was developed. Zoning of land became commonplace and classification as improved or unimproved was designated. Governments believed building upon the land improved it because such lands generated greater tax revenue. But from an environmental perspective, these projects were not improvements but environmentally liabilities increasing in cost over time.

Thus the paradox. Often, urban governments have autonomy over local land decisions. As a result, property is taxed and local governments funded. Government revenue increases with land improvements creating the need to grow in order to meet increasing population demands. Local governments find the need to approve

*Degradation and Improvement of Urban River Water Quality DOI: http://dx.doi.org/10.5772/intechopen.98694*

**Figure 1.** *A river flowing through the urban landscape.*

development to support its infrastructure and the cycle continues. It is difficult to suggest stopping this because you are asking government to stop funding the essential services you need such as police, fire protection, schools and roads.

As this development continued, groups of environmental researchers began to observe how rivers were responding. Leopold et al. [1] called it the urbanization cycle where heavy development caused rapid sedimentation followed by fundamental changes in river hydrology. In the same year, Walsh et al. [2] along with Meyer et al. [3] coined the term urban stream syndrome. The descriptions were alarming. With development, the stream channel begins to deepen and widen with the banks becoming unstable and eroding. Deepening of the river isolates it from the floodplain resembling a simple conveyance rather than an integrated stream course. Continued overdevelopment isolates remaining ecological services provided by trees, soil and wildlife. As waste and energy needs for the urban system intensifies, the cycle of erosion and isolation continues (**Figure 1**).
