Why rehabilitate urban river systems

This increase can be attributed to the hydraulic structures and to external factors, such as wastewater discharge from irregular settlements in the lower drainage basins and surface runoff during the rainy season.

The hydrological histogram Figure 3 shows the discrepancy in hydrological conditions: under low-flow conditions, the mRFR curve corresponds to the NFR conditions. Therefore, the minimum regulated behavior mimics a natural condition. Figure 4 depicts the annual flow over a year period. In the s, the development of hydraulic infrastructure in the river caused a laminar flow effect. Average, maximum and minimum flows.

The behavior of the mean annual flows Figure 4 also reflects the effect of regulation. Although the mean flow in both periods is very similar, namely, 0. Over time, extraction from the river has been balanced by wastewater inputs into the river, which has led to an increase of 0.

The exchange of clean water for untreated wastewater has significantly degraded the environmental condition of the river. There are only two direct discharge points into the river over the course of the distance from its origin to the treatment plant; in contrast, after the treatment plant, 58 inputs are known [12]. Irregular settlements are problematic because they often lack a sewer system, thereby allowing wastewater to flow directly into the rock or soil and hence toward the lower discharge area where the river is located.

In Figure 5 , a historical annual comparative analysis illustrates the natural flow from to in two flow-duration curves; during this time, the annual mean flow at the lower point of the Magdalena river was at least 0. High flows with flows of approximately 1. In the s, the development of hydraulic infrastructure in the river caused a laminar flow effect; therefore, in the curve for the regulated period from —, the mean flow at the river is at least 0.

It is also possible to observe changes to the slope of the natural flow curve reference with respect to the regulated flow curve, specifically, changing from 0. The behavior of the natural curve of collected frequencies to depicted in Figure 5 is representative of mountain rivers; therefore, based on the flow duration curve observed for the regulated period to , a new behavior is observed.

That is, the river is behaving if it were a floodplain river, where changes are less apparent. Generally, this response is due to changes to the flow of the Magdalena River as a result of anthropogenic activities, with an associated increase in the concentration of several water quality variables. Figure 6 shows the distribution of water flux for the rainy and dry seasons for the years —, starting with the dry season from January-April , followed by the rainy season of , the dry season from November —April , and so on.

The figure demonstrates that the mean value is relatively constant for dry and rainy seasons, while the variability changed during those same years; hence, no pattern can be observed for the changes in variability.

This is related to the high variability of the amount of rain falling in the upper parts of the basin, particularly during the rainy season of The low variability for the dry season from November—December is due in part to the small amount of data for this time lapse. The spatial and temporal analyses for the physicochemical variables and nutrients are presented in Figures 7 and 8.

These variables are those most representative of river water quality, such as electrical conductivity, dissolved oxygen, ammonia, total N, orthophosphates and total P, as well as fecal coliforms and fecal enterococci. These variables are considered representative because they have the highest absolute value in the factor loadings of the first three principal components.

Although the number of samples at each site was not the same, it only affects the variance of the mean values of the measured water properties. The GLM models fitted to the water quality variables [38] indicate statistically significant differences for all of the variables, except dissolved oxygen, in the upper and lower sections of both rivers. The point of change was the location at which human activities and settlements began on either or both river banks.

Water quality variables sampled upstream of these urban areas fell within acceptable limits for use as a water supply. The values gradually fell to lower quality as the sampling sites became increasingly affected by the wastewater generated in the irregularly inhabited areas.

The spatial trends along the river gradient for the eight most-relevant water quality attributes are shown as box plots in Figure 7 for the Magdalena River and in Figure 8 for the Eslava River. The plot shows a change point at site M9, which is located at the border between the natural and urban areas: here, increasing concentrations of all values can be observed, except that of dissolved oxygen, which decreases. The highest concentrations were detected at site M15, where part of the water is piped to the city's drainage system.

These values then decrease slightly at sites M17 and M18, where other effluents with residual water from the southern area of the city join the waterway. In the Eslava River, all variables except dissolved oxygen are significantly different between the natural and urban areas, a change that occurs somewhere between E5 and E6.

Further, all variables exhibit stable values until the confluence point. The Eslava River has lower water quality than the Magdalena River does at the confluence point, particularly in terms of electrical conductivity, the value of which is six times higher in the Eslava River; additionally, the value of total N is three times higher, while that of total P is twice the concentration of that in the Eslava River.

The fecal enterococci values were three times as large on a log scale, which means that this measurement is 1, times greater. Please note this difference in the values of the axes on the graphs.

At E7, the values are slightly above the limit. Taking this into account, the fecal coliforms surpass the limit and require treatment before distribution through the southern parts of the city. The standards are met at the Potabilization Plant La Magdalena, but there are many water intakes near settled populations in an irregular land ownership situation, which means that these populations are exposed to high levels of bacteria; this is an important risk factor that should be taken into further account.

The bacterial isolates and identifications obtained from water samples taken from the Magdalena River in the period to are presented in Table 2. These belong to nine different families and 18 genera [26] , [46]. The most abundant genera were Enterococcus , Escherichia coli , Enterobacter and Klebsiella.

From the Eslava River, 27 bacterial isolates and identifications were obtained from water samples taken during These belong to four different families and seven genera, as reported in Table 3. Therefore, a variety of bacteria belonging to a total of 20 different genera were identified in the river system crossing the southern area of Mexico City.

The most prevalent bacteria were from the Enterococcaceae family, Enterococcus , and from the Enterobacteriaceae family, Escherichia , Enterobacter and Klebsiella. Although these results serve as an initial approach to the identification of bacteria, it is important to note that all of these bacteria are common to the human gut and can be opportunistic pathogens that may cause illness to immune-compromised people who access this water when untreated. The presence of coliphage was measured by bacterial hosts in samples from the urban zone; this finding is consistent with the inputs of raw and untreated wastewater to the Magdalena River Table 4.

As host bacteria, E. It is important to note that there are two infection mechanisms of interest, either by adherence to the cell wall or infection via pilli, as in the coliphage F-specific [47] , [48] , [49] , [50]. Therefore, the host is more susceptible to infection and shows higher counts.

In the natural area sites, no coliphage presence was detected, which suggests that perturbation does not have a detectable impact using this method. Generally, the presence of a phage indicates fecal contamination by a virus; however, this level of analysis is not conclusive because it cannot establish the contaminants' origin, namely, whether human or animal.

In urban areas, coliphages are present from the transition zone between the natural and urban zones, where the highest density was detected at site M19; hence, the number of phages increases with human perturbation and influence. Both adenovirus AdV F and enterovirus EV exclusively affect humans; their presence indicates human fecal contamination [51] , [52]. Once these viral particles have been excreted into the environment, their number cannot increase because the presence of the cell host is required for their replication [53].

Therefore, the detection of AdV and EV reflects the fact that in the human population, the virus is circulating and replicating. This constitutes a threat that must be considered regarding the river because these viruses can cause infections to susceptible individuals, yielding viral gastroenteritis.

Such infections mainly occur in children under five years of age because adults who were infected as young children often acquire immunity [52].

Nevertheless, if adults are exposed to viral particles, they can be asymptomatically reinfected, with a lower amount of viral particles excreted in their feces. This can favor the dispersion of AdV F because these individuals will not be cautious in their behaviors because they are asymptomatic.

People can present infections and acute gastroenteritis as a result of AdV F [54]. Due to the relevance of this virus as a gastroenteritis-causing agent, it is considered the second-most important virus after rotavirus worldwide [56] ; therefore, it is important to monitor the prevalence of this virus both in the human population and in residual water as an indicator of what is infecting a given population. According to our results Table 4 , AdV F is present at both the natural and urban sites, indicating human fecal contamination in both locations.

The presence of AdV F at the river origin M1 could represent an isolated contamination event because it was only detected at a low density in the samples from this site. The presence of human fecal contamination coincides with the irregular settlements that discharge their wastewater directly to the river. Because the system once flowed continuously, the viral contamination issue is likely a recent phenomenon.

Wastewater discharge is constant; unsurprisingly, the higher amounts of AdV F viral particles were detected in the urban zone due to wastewater discharge without proper treatment [54] , [57]. It is important to note that the number of AdV F particles can represent an important mechanism of exposure to the population, primarily for children under five, who may be more likely to come in direct contact with the water in urban areas; accordingly, this exposure can lead to moderate to severe gastroenteritis [53].

For the exposure dose, a point estimate was reported by Crabtree et al. Based on this finding, a 2 infectious viral particle can be considered the probability for infection based on an average dose of 1. Nevertheless, the fact that the genome detection rate is commonly larger than the number of viral particles [60] clearly demonstrates that the detection capacity of 10 genome copies is adequate for the identification of adenovirus as a hazard.

Cryptosporidium parvum and Giardia lamblia are the most common intestinal protozoa in the environment, commonly infecting both humans and domestic and wild animals [61]. These protozoa are among the main disease-causing agents of diarrhea in the world [62].

Both species form resistance structures that allow them to survive outside the host; they can thus be transmitted through water [63]. Additionally, both species have a low infective dose ID 50 , specifically, Cryptosporidium spp. Thus, a potential host consuming a low number of these microorganisms can readily develop an infection.

Based on these facts, the detection of C. Children between 0 and 14 years of age and immunodeficient persons are susceptible. The range in the natural zone was lower for both species 0—1, oocysts of C.

This can be explained by the input of wastewater from the urban area [12]. Untreated water could be increasing the number of oocysts present in the zone, leading to a potential population exposure risk because the population densities range from 1—2 log units more than the infective dose.

Because these rivers represent the only surface water source from within the Basin for Mexico City, particular concern should be held regarding the presence of certain microorganisms, such as the protozoa Giardia and Cryptosporidium and adenovirus, which are relatively resistant to the chlorination process in comparison to other microorganisms.

Physical removal is critical to the control of Cryptosporidium because the organism is highly resistant to standard disinfection practices [66] , [67]. As mentioned by Betancourt and Rose [68] , the effectiveness of conventional disinfection by chlorination and alternative disinfection procedures, such as chlorine dioxide, ozonation and ultraviolet irradiation UV , toward inactivating Cryptosporidium has been the focus of current research. The goals for systems that treat surface water must be disinfection and filtration to remove or inactivate In Mexico and other developing countries, modern treatment processes should be applied, given the presence of these microorganisms in the surface waters.

One of the first steps when dealing with rivers is understanding their flow and any variations that occur throughout the year and across different years.

In Mexico, monitoring practices were initiated but have since been abandoned for many rivers throughout the country.

A sustainable approach to water management, especially in light of climate change, would be to monitor and report environmental and social conditions to provide a guide toward a more sustainable water management strategy.

The regimes of the Magdalena and Eslava rivers belong to homonymous basins that have been modified, and both exhibit two distinct historical periods. The periods are defined by the construction of excess hydraulic infrastructure works, such as gabion dams, 50 on the Magdalena and 18 on the Eslava Figure 1 , and marginal drains.

This NFR alteration will certainly have consequences for the river communities in the natural area and for system rehabilitation. These regime changes may contribute to the observed water quality degradation and contamination of the systems because the loss of velocity along a slope and other discontinuities in the river affect the inherent auto-depuration processes.

As recorded in our fieldwork, the observed higher concentrations of the physicochemical variables indicate the presence of higher levels of contaminants in the lower section of both basins, especially as the urban zone is entered. Wastewater discharges also contribute to the degradation of water quality.

Hence, even if discharge does not contribute significantly to flow volume, its effect on water quality is magnified due to the decrease in flow velocity. Further, wastewater discharge increases the concentrations of various water quality attributes.

In some rivers, contaminants are diluted through their tributaries. However, in this case, the Eslava River contributes its own contaminant load, which for some variables is orders of magnitude higher than the Magdalena's water, thereby hampering the auto-depuration process. It is necessary to treat the residual wastewater dumped into the river and recover the fluvial processes and function of the rivers as ecosystems.

This approach would provide several advantages. For example, there would be more water produced in the higher basin, which could be disinfected and distributed to the population.

Additionally, a decrease in the amount of water that flows to the drainage system and that must be pumped out of the Basin of Mexico would be realized, as well as additional amounts of water once the wastewater has been treated and reused for irrigation near the river. Area Key words: Australia, legislation, prioritization, rehabilitation, rivers, urban Introduction Urban river systems are often heavily degraded,a situation that is not confined to a particulargeographic region of the world, but common to allareas subject to urbanization Morley and Karr Questions relatingto social, political and economic issues can beextremely relevant in these urban stream systemswhere ecological integrity is compromised for flood mitigation and waste water control.

What is rehabilitation? Rutherfurd et al. Ecosystem function or biomass is represented by the number of individuals present within a system and is essentially an indication of productivity figure adapted and modified from Rutherfurd et al. In Australia these definitionsare generally accepted by practitioners Abernethyand Wansbrough ; Bennett et al.

In contrast, rehabilitation des-cribes a condition along the same vector as restor-ation, where elements of the natural biophysicalsystem are returned, but not all Rutherfurd et al. Rhoads et al. Physical integrity Riverine management has evolved from a pre-dominately engineering focus towards one wheregeomorphology and ecology are now taking a moreprominent role in the decisionmaking process Hooke ; Douglas ; Logan ; Morleyand Karr The physical integrity of a streamis now seen by many as the fundamental scaleon which to base river rehabilitation Brierley andFryirs ; Taylor et al.

Recently,these aspects have formed the basis of many riverclassifications Whiting and Bradley ; Rosgen; Chessman ; Brierley and Fryirs ,including those specific to urban areas Anderson; Gregory and Chin ; Chin and Gregory Stream hydrology The hydrological characteristics of urban catch-ments are often a primary determinant influencinghow a system, as a whole, responds to urbanization.

Increases in the impervious surface cover thataccompanies urbanization alters stream hydrology,forcing runoff to occur more readily and quicklyduring rainfall events, thus decreasing the amount oftime it takes water to reach streams Leopold ;May et al. This processsubsequently increases the flows for any givenrainfall event, causing runoff of peak flows with arecurrence interval of 2 years to increase by factorsof two, three and five with 10, 15 and 30 per centimpervious development respectively Hammer; Hollis , or a 1 in 5 year event occurringtwice a year Wong et al.

Major physiographic Documents. Retention areas are meant to receive the peak discharge of rivers and therefore to prevent flooding elsewhere. Emergency retention areas can be located along the major rivers to receive large quantities of water in extreme conditions to prevent life-threatening situations and large damage elsewhere in e.

The cost of these measures can be high in case of need for expropriation, demolition and re-building elsewhere of infrastructure and economic activities. Rivers and floodplains in relocated areas have a high potential for restoration, which offers not only improved habitats, but contributes to flood protection by creating new retention areas. In some specific cases, measures may also deal with the adaptation of dredging practices to changes in water depth, navigability, erosion and siltation in rivers.

Applying and financing rehabilitation of the river and its floodplains, also as a compensatory approach of the deepening of the navigation channel, can ensure that habitats and their services such as flood protection are maintained. This programme included a number of measures leading to the rehabilitation and restoration of river beds and floodplains, to create more room for the rivers and reduce water levels, such as: lowering of the floodplains, relocating dikes further inland, lowering levees along the rivers and deepening the summer beds.

Other examples are the Anglian River Basin Management Plan in the United Kingdom, which includes various river restoration projects aiming to mitigate the impacts of hydro-morphological modifications.

These projects are often set up and implemented by encouraging cooperation between water engineering, flood protection, land management and nature conservation.

Structural and physical: Ecosystem-based adaptation options. Stakeholder participation. The implementation of this adaptation option requires the involvement of various actors river managers, farmers, inhabitants of villages, etc. Early engagement of key stakeholders is essential to correctly manage any conflicts, e. Success and Limiting Factors.

Implementation of river and floodplain restoration measures can have negative effects on navigation, and varying effects both positive and negative on tourism, agriculture and drainage.

In general it is intended to have positive effects on biodiversity and habitat conservation. However, it is not always feasible to implement because sometimes the artificialized river margins do not allow natural restoration of the river.

Success factors generally include strong cooperation among public administrations and other stakeholders, raising support and creating public awareness. Link to publication in Scopus. Fingerprint Dive into the research topics of 'Why rehabilitate urban river systems? Together they form a unique fingerprint. View full fingerprint.