ENVIRONMENTAL IMPACT OF CHANNEL MODIFICATION1

ABSTRACT: The purpose of this literature review is to identify and quantify the effects of channelization and to examine the feasibility and acceptability of alternative methods of flood control. In the past 150 years, over 200,000 miles of stream channels have been modified. Channelization can affect the environment by draining wetland, cutting off oxbows and meanders, clearing floodplain hardwoods, lowering ground water levels, reducing ground water recharge from stream flow, and increasing erosion sedimentation, channel maintenance, and downstream flooding. Channelization reduces the size, number, and species diversity of fish in streams. In a wet climate, the fishery requires less than 10 years to fully recover. However, in the drier climates, the fishery may never fully recover. In general, channel modifications have performed as designed for flood abatement. The Arthur D. Little Study (1973) reported that direct benefits estimated during channelization planning have been conservative and that damage reduction has been impressive. Diking seems to be a viable alternative to channel dredging. Dikes minimize destruction of wetland and eliminate the need for removing vegetation from the existing stream banks.     

The Effect of Channelization on Floodplain Sediment Deposition and Subsidence Along the Pocomoke River,Maryland1

Kroes, Daniel E. and Cliff R. Hupp, 2010. The Effect of Channelization on Floodplain Sediment Deposition and Subsidence Along the Pocomoke River, Maryland. Journal of the American Water Resources Association (JAWRA) 46(4): 686-699. DOI: 10.1111/j.1752-1688.2010.00440.x Abstract: The nontidal Pocomoke River was intensively ditched and channelized by the mid-1900s. In response to channelization; channel incision, head-cut erosion, and spoil bank perforation have occurred in this previously nonalluvial system. Six sites were selected for study of floodplain sediment dynamics in relation to channel condition. Short- and long-term sediment deposition/subsidence rates and composition were determined. Short-term rates (four years) ranged from 0.6 to 3.6 mm/year. Long-term rates (15-100+ years) ranged from −11.9 to 1.7 mm/year. ¹³⁷Cs rates (43 years) indicate rates of 0.24 to 7.4 mm/year depending on channel condition. Channelization has limited contact between streamflow and the floodplain, resulting in little or no sediment retention in channelized reaches. Along unchannelized reaches, extended contact and depth of river water on the floodplain resulted in high deposition rates. Drainage of floodplains exposed organic sediments to oxygen resulting in subsidence and releasing stored carbon. Channelization increased sediment deposition in downstream reaches relative to the presettlement system. The sediment storage function of this river has been dramatically altered by channelization. Results indicate that perforation of spoil banks along channelized reaches may help to alleviate some of these issues.     

HYDROLOGIC STAGE PERIODICITY OF THE MISSISSIPPI RIVER BEFORE AND AFTER SYSTEMATIC CHANNEL MODIFICATIONS1

ABSTRACT: Periodic flood disturbance is a well known controlling factor of in channel and floodplain ecosystem function. However, channel manipulations during the last century have potentially altered hydrologic fluctuations, and thus ecosystem function. We examined temporal river stage hydrology, through autocorrelation analysis, at seven gauges along the Mississippi River to quantify flow periodicity and effects of systematic channel modifications on flow periodicity. Intraannual variation follows a strong one‐year cycle of six months higher flow and six months lower flow for the entire Mississippi River drainage, with precipitation as a driving force. Interannual hydrologic variation differs between the upper and lower river segments. A clear quasi‐biennial oscillation pattern was evident throughout the lower river section. The effect of channel alterations was a decreased magnitude of differences between lower and higher flows. The upper section, however, suggests a 12‐to 14‐year periodicity prior to alterations and a decreased duration of lower flow years following systematic modifications. Interannual variograms clearly depict very different temporal hydrology between the upper Mississippi River and the lower Mississippi River, suggesting the simple transfer of knowledge from one segment to the other oversimplifies the complexity of a large river system.     

Pre-instrumental perspectives on Arkansas River cross-watershed flow variability

We present four reconstruction estimates of Arkansas River baseflow and streamflow using a total of 78 tree-ring chronologies for three streamflow gages, geographically spanning the headwaters in Colorado to near the confluence of the Arkansas-Mississippi rivers. The estimates represent different seasonal windows, which are dictated by the shared limiting forcing of precipitation on seasonal tree growth and soil moisture—and subsequently on the variability of Arkansas River discharge. Flow extremes that were higher and lower than what has been observed in the instrumental era are recorded in each of the four reconstructions. Years of concurrent, cross-basin (all sites) low flow appear more frequently during the 20th and 21st Centuries compared to any period since 1600 A.D., however, no significant trend in cross-basin low flow is observed. As the most downstream major tributary of the Mississippi River, the Arkansas River directly influences flood risk in the Lower Mississippi River Valley. Estimates of extreme high flow in downstream reconstructions coincide with specific years of historic flooding documented in New Orleans, Louisiana, just upstream of the Mississippi River Delta. By deduction, Mississippi River flooding in years of low Arkansas River flow imply exceptional flooding contributions from the Upper Mississippi River catchments.     

Stream renovation: An alternative to channelization

Channelization is one of the most common solutions to urban drainage problems, despite the fact that channelized streams are frequently morphologically unstable, biologically unproductive, and aesthetically displeasing. There is increasing empirical and theoretical evidence to suggest that channelization may be counterproductive unless channels are designed to prevent the bank erosion and channel silting that often accompanies stream dredging. Many of the detrimental effects of channelization can be avoided, with little compromise in channel efficiency, by employing channel design guidelines that do not destroy the hydraulic and morphologic equilibria that natural streams possess. These guidelines include minimal straightening; promoting bank stability by leaving trees, minimizing channel reshaping, and employing bank stabilization techniques; and, emulating the morphology of natural stream channels. This approach, called stream restoration or stream renovation, is being successfully employed to reduce flooding and control erosion and sedimentation problems on streams in Charlotte, North Carolina.     

Flood control failure: San Lorenzo River,California

The San Lorenzo River on the central California coast was the site of a major US Army Corps of Engineers flood control project in 1959. By excavating the channel below its natural grade and constructing levees, the capacity of the river was increased in order to contain approximately the 100 year flood. Production and transport of large volumes of sediment from the river's urbanizing watershed has filled the flood control project with sand and silt. The natural gradient has been re-established, and flood protection has been reduced to containment of perhaps the 30 year flood. In order for the City of Santa Cruz, which is situated on the flood plain, to be protected from future flooding,it must either initiate an expensive annual dredging program, or replan and rebuild the inadequately designed flood control channel. It has become clear, here and elsewhere, that the problem of flooding cannot simply be resolved by engineering. Large flood control projects provide a false sense of security and commonly produce unexpected channel changes.     

Nutrient and sediment concentrations and corresponding loads during the historic June 2008 flooding in eastern Iowa

A combination of above-normal precipitation during the winter and spring of 2007-2008 and extensive rainfall during June 2008 led to severe flooding in many parts of the midwestern United States. This resulted in transport of substantial amounts of nutrients and sediment from Iowa basins into the Mississippi River. Water samples were collected from 31 sites on six large Iowa tributaries to the Mississippi River to characterize water quality and to quantify nutrient and sediment loads during this extreme discharge event. Each sample was analyzed for total nitrogen, dissolved nitrate plus nitrite nitrogen, dissolved ammonia as nitrogen, total phosphorus, orthophosphate, and suspended sediment. Concentrations measured near peak flow in June 2008 were compared with the corresponding mean concentrations from June 1979 to 2007 using a paired t test. While there was no consistent pattern in concentrations between historical samples and those from the 2008 flood, increased flow during the flood resulted in near-peak June 2008 flood daily loads that were statistically greater (p < 0.05) than the median June 1979 to 2007 daily loads for all constituents. Estimates of loads for the 16-d period during the flood were calculated for four major tributaries and totaled 4.95 x 10(7) kg of nitrogen (N) and 2.9 x 10(6) kg of phosphorus (P) leaving Iowa, which accounted for about 22 and 46% of the total average annual nutrient yield, respectively. This study demonstrates the importance of large flood events to the total annual nutrient load in both small streams and large rivers.     

CHANNELIZATION AND INVERTEBRATE DRIFT IN SOME IOWA STREAMS1

ABSTRACT: Habitat diversity and invertebrate drift were studied in a group of natural and channelized tributaries of the upper Des Moines River during 1974 and 1975. Channelized streams in this region had lower sinuosity index values than natural channel segments. There were significant (P=O.05) positive correlations between channel sinuosity and the variability of water depth and current velocity. Invertebrate drift density, expressed as biomass and total numbers, also was correlated with channel sinuosity. Channelization has decreased habitat variability and invertebrate drift density in streams of the upper Des Moines River Basin and probably has reduced the quantity of water stored in streams during periods of low flow.     

ASSESSING FLOOD MITIGATION ALTERNATIVES IN SHIJR AREA IN METROPOLITAN TAIPEI1

The Keelung River Basin in northern Taiwan lies immediately upstream of the Taipei metropolitan area. The Shijr area is in the lower basin and is subject to frequent flooding. This work applies micromanagement and source control, including widely distributed infiltration and detention/ retention runoff retarding measures, in the Wudu watershed above Shijr. A method is also developed that combines a genetic algorithm and a rainfall runoff model to optimize the spatial distribution of runoff retarding facilities. Downstream of Wudu in the Shijr area, five dredging schemes are considered. If 10‐year flood flows cannot be confined in the channel, then a levee embankment that corresponds to the respective runoff retarding scheme will be required. The minimum total cost is considered in the rule to select from the regional flood mitigation alternatives. The results of this study reveal that runoff retarding facilities installed in the upper and middle parts of the watershed are most effective in reducing the flood peak. Moreover, as the cost of acquiring land for the levee embankment increases, installing runoff retarding measures in the upper portion of the watershed becomes more economical.     

FLOOD HAZARD STUDIES IN THE MISSISSIPPI RIVER BASIN USING REMOTE SENSING1

ABSTRACT. The Spring 1973 Mississippi River flood was investigated using remotely sensed data from ERTS-1. Both manual and automatic analyses of the data indicate that ERTS-I is extremely useful as a regional tool for flood management. Quantitative estimates of area flooded were made in St. Charles County, Missouri and Arkansas. Flood hazard mapping was conducted in three study areas along the Mississippi River using pre-flood ERTS-1 imagery enlarged to 1:250,000 and 1:100,000 scale. The flood prone areas delineated on these maps correspond to areas that would be inundated by significant flooding (approximately the 100 year flood). The flood prone area boundaries were generally in agreement with flood hazard maps produced by the U. S. Army Corps of Engineers and U. S. Geological Survey although the latter are somewhat more detailed because of their larger scale. Initial results indicate that ERTS-1 digital mapping of flood prone areas can be performed at 1:62,500 which is comparable to some conventional flood hazard map scales.     

NEW DIRECTIONS IN FLOODPLAIN MANAGEMENT1

ABSTRACT: Over the last 30 years, average annual riverine flood damages have exceed $2 billion. Damages associated with the Mississippi River Flood of 1993 exceeded $12 billion and these costs do not include the non-quantifiable, human impacts of this disaster. In a report submitted to the White House in June 1994, a federal interagency floodplain management review committee proposed better ways to manage the nation's floodplains. The committee indicated that the 1993 Mississippi River flood was the result of a significant hydrometeorological event, that federal flood control efforts in the Mississippi basin had prevented nearly $20 billion in potential damages, and that, in spite of federal flood damage reduction efforts, throughout the nation people and property remain at risk to inevitable future flooding. It recommended that the division of decision and cost-sharing responsibilities among federal, state and local governments be more clearly defined, and that the nation adopt a strategy of, sequentially, avoiding inappropriate use of the flood-plain, minimizing vulnerability to damage through both nonstruc-tural and structural means, and mitigating damages as they occur. The report did not call for abandonment of human use of the flood-plain but argued for full consideration of the economic, social and environmental costs and benefits of all future floodplain activity.     

ADJUSTMENT OF STREAM CHANNEL CAPACITY FOLLOWING DAM CLOSURE,YEGUA CREEK,TEXAS1

ABSTRACT: In Yegua Creek, a principal tributary of the Brazos River in Texas, surveys of a 19 km channel reach downstream of Somerville Dam show that channel capacity decreased by an average of 65 percent in a 34 year period following dam closure. The decrease corresponds with an approximately 85 percent reduction in annual flood peaks. Channel depth has changed the most, decreasing by an average of 61 percent. Channel width remained stable with an average decrease of only 9 percent, reflecting cohesive bank materials along with the growth of riparian vegetation resulting from increased low flows during dry summer months. Although large changes in stream channel geometry are not uncommon downstream of dams, such pronounced reductions in channel capacity could have long‐term implications for sediment delivery through the system.     

DAM‐INDUCED MODIFICATIONS TO UPPER ALLEGHENY RIVER STREAMFLOW PATTERNS AND THEIR BIODIVERSITY IMPLICATIONS1

ABSTRACT: This study evaluates the streamflow characteristics of the upper Allegheny River during the periods preceding (1936 to 1965) and following (1966 to 1997) completion of the Kinzua Dam in northwestern Pennsylvania. Inter‐period trends in seasonal patterns of discharge and peak flow at three downstream sites are compared to those at two upstream sites to determine the influence of this large dam on surface water hydrology. Climatic records indicate that significant changes in annual total and seasonal precipitation occurred over the twentieth century. Increased runoff during the late summer through early winter led to increased discharge both upstream and downstream during these months, while slightly less early‐year rainfall produced minor reductions in spring flood peaks since 1966. The Kinzua Dam significantly enhanced these trends downstream, creating large reductions in peak flow, while greatly augmenting low flow during the growing season. This reduction in streamflow variability, coupled with other dam‐induced changes, has important biodiversity implications. The downstream riparian zone contains numerous threatened/endangered species, many of which are sensitive to the type of habitat modifications produced by the dam. Flood dynamics under the current post‐dam conditions are likely to compound the difficulties of maintaining their long‐term viability.     

Effect of Human Activities on Overall Trend of Sedimentation in the Lower Yellow River,China

The Yellow River has been intensively affected by human activities, particularly in the past 50 years, including soil–water conservation in the upper and middle drainage basin, flood protection in the lower reaches, and flow regulation and water diversion in the whole drainage basin. All these changes may impact sedimentation process of the lower Yellow River in different ways. Assessing these impacts comprehensively is important for more effective environmental management of the drainage basin. Based on the data of annual river flow, sediment load, and channel sedimentation in the lower Yellow River between 1950 and 1997, the purpose of this paper is to analyze the overall trend of channel sedimentation rate at a time scale of 50 years, and its formative cause. It was found in this study that erosion control measures and water diversion have counteractive impacts on sedimentation rate in the lower Yellow River. Although both annual river flow and sediment decreased, there was no change in channel sedimentation rate. A regression analysis indicated that the sedimentation in the lower Yellow River decreased with the sediment input to the lower Yellow River but increased with the river flow input. In the past 30–40 years, the basin-wide practice of erosion and sediment control measures resulted in a decline in sediment supply to the Yellow River; at the same time, the human development of water resources that required river flow regulation and water diversion caused great reduction in river flow. The former may reduce the sedimentation in the lower Yellow River, but the reduction of river flow increased the sedimentation. When their effects counterbalanced each other, the overall trend of channel sedimentation in the lower Yellow River remained unchanged. This fact may help us to better understand the positive and negative effects of human activities in the Yellow River basin and to pay more attention to the negative effect of the development of water resources. The results of this study demonstrate that, if the overuse of river water cannot be controlled, the reduction of channel sedimentation in the lower Yellow River cannot be realized through the practice of erosion and sediment control measures.     

CLIMATE VARIABILITY AND FLOOD FREQUENCY ESTIMATION FOR THE UPPER MISSISSIPPI AND LOWER MISSOURI RIVERS1

ABSTRACT: This paper considers the distribution of flood flows in the Upper Mississippi, Lower Missouri, and Illinois Rivers and their relationship to climatic indices. Global climate patterns including El Niño/Southern Oscillation, the Pacific Decadal Oscillation, and the North Atlantic Oscillation explained very little of the variations in flow peaks. However, large and statistically significant upward trends were found in many gauge records along the Upper Mississippi and Missouri Rivers: at Hermann on the Missouri River above the confluence with the Mississippi (p = 2 percent), at Hannibal on the Mississippi River (p < 0.1 percent), at Meredosia on the Illinois River (p = 0.7 percent), and at St. Louis on the Mississippi below the confluence of all three rivers (p = 1 percent). This challenges the traditional assumption that flood series are independent and identically distributed random variables and suggests that flood risk changes over time.     

A HYDROCLIMATOLOGICAL ANALYSIS OF THE RED RWER OF THE NORTH SNOWMELT FLOOD CATASTROPHE OF 19971

ABSTRACT: The flood hydroclimatology of the Grand Forks flood of April 1997, the most costly flood on a per capita basis for a major metropolitan area in United States history, is analyzed in terms of the natural processes that control spring snowmelt flooding in the region. The geomorphological characteristics of the basin are reviewed, and an integrated assessment of the hydroclimatological conditions during the winter of 1996 to 1997 is presented to gain a real‐world understanding of the physical basis of this catastrophic flood event. The Grand Forks flood resulted from the principal flood‐producing factors occurring at either historic or extreme levels, or at levels conducive to severe flooding. Above normal fall precipitation increased the fall soil moisture storage and reduced the spring soil moisture storage potential. A concrete frost layer developed that effectively reduced the soil infiltration capacity to zero. Record snowfall totals and snow cover depths occurred across the basin because of the unusual persistence of a blocking high circulation pattern throughout the winter. A severe, late spring blizzard delayed the snowmelt season and replenished the snow cover to record levels for early April. This blizzard was followed by a sudden transition to an extreme late season thaw due to the abrupt breakdown of the blocking circulation pattern. The presence of river ice contributed to backwater effects and affected the timing of tributary inflows to the main stem of the Red River. Only the absence of spring rains prevented an even more catastrophic flood disaster from taking place. This paper contributes to our understanding of the flood hydroclimatology of catastrophic flood events in an unusual flood hazard region that possesses relatively flat terrain, a north‐flowing river, and an annual peak discharge time series dominated by spring snowmelt floods.     

BENTHIC INVERTEBRATES OF THE LOWER MISSISSIPPI RIVER1

ABSTRACT: In 1976–77, benthic invertebrates were sampled at four sites in a 410-kilometer reach of the lower Mississippi River to define the communities in the river and to determine differences between communities upstream and downstream from the industrial and municipal complexes of Baton Rouge and New Orleans, Louisiana. The most common and most numerous organisms collected were Corbicula and tubificid worms. The benthic community structure of the lower Mississippi River is influenced by substrate type and stability, channel geometry, river velocity, vegetation and organic detritus, and salinity. Sampling stations near the left and right banks had low velocities, and substrate types ranged from medium silt to very fine sand. Burrowing organisms such as tubificids, chironomids, and ephemerid-type mayflies dominated these environments. At the center, left-center, and right-center stations, velocities were higher and substrate materials were coarser than at the bank stations; only Corbicula was present in large numbers. Near the river mouth, salinity and aquatic vegetation greatly affect the benthic community structure. Differences in benthic community structure in the Mississippi River are due primarily to different hydrologic conditions. Industrial and municipal wastes discharged into the river appear to have little or no widespread effects on benthic populations.     

Characterizing Geomorphic Change from Anthropogenic Disturbances to Inform Restoration in the Upper Cache River,Illinois

Over the past century, channelization, agricultural tiling, and land use changes have resulted in significant stream channel degradation of the Cache River in southern Illinois. With the increasing interest in restoration of the watershed's bottomland forests and swamps, we sought to characterize geomorphic change over the past 110 years to inform restoration and management. A previously surveyed stretch of river was resurveyed in the fall of 2011, following a record flood in the spring of that year. Results suggest that the slope of the channel in this section of the river has increased 345% between 1903 and 1972 (p < 0.01), but has not changed significantly since (p = 0.12). Within that same time period, bank heights increased between 1 and 7 m and bed elevation decreased between 1 and 5 m. Changes in resurveyed cross sections appear to be primarily due to recent flood scour. It appears as though early 20th Century stream channel modifications had immediate effects on the geomorphology of the channel; however, channel geometry is now at or near equilibrium. This case study of the Cache River watershed demonstrates how and why successful restoration will require integration of geomorphic processes of the system.     

A geomorphologist's criticism of the engineering approach to channelization of gravel-bed rivers: case study of the Raba River, Polish Carpathians

River engineers use sediment transport formulas to design regulated channels in which the river's ability to transport bedload would remain in equilibrium with the delivery of materials from upstream. In gravel-bed rivers, a number of factors distort the simple relationship between particle size and hydraulic parameters at the threshold of sediment motion, inherent in the formulas. This may lead to significant errors in predicting the bedload transport rates in such streams and hence to instability of their regulated channels. The failure to recognize a nonstationary river regime may also result in unsuccessful channelization. Rapid channel incision has followed channelization of the main rivers of the Polish Carpathians in the 20th century. A case study of the Raba River shows that incision has resulted from the increase in stream power caused by channelization and the simultaneous reduction in sediment supply due to variations in basin management and a change in flood hydrographs. Calculations of bedload transport in the river by the Meyer-Peter and Müller formula are shown to have resulted in unrealistic estimates, perhaps because the different degree of bed armoring in particular cross-sections was neglected. It would have been possible to avoid improper channelization if the decreasing trend in sediment load of the Carpathian rivers had been recognized on the basis of geomorphological and sedimentological studies. Allowing the rivers to increase their sinuosity, wherever possible without an erosional threat to property and infrastructure, and preventing further in-stream gravel mining are postulated in order to arrest channel incision and reestablish the conditions for water and sediment storage on the floodplains.     

Impact of floodplain and Stage 0 stream restoration on flood attenuation and floodplain exchange during small frequent storms

River flooding impacts human life and infrastructure, yet provides habitat and ecosystem services. Traditional flood control (e.g., levees, dams) reduces habitat and ecosystem services, and exacerbates flooding elsewhere. Floodplain restoration (i.e., bankfull floodplain reconnection and Stage 0) can also provide flood management, but has not been sufficiently evaluated for small frequent storms. We used 1D unsteady Hydrologic Engineering Center's River Analysis System to simulate small storms in a 5 km-long, second-order generic stream from the Chesapeake Bay watershed, and varied % channel restored (starting at the upstream end), restoration location, restoration bank height (distinguishes bankfull from Stage 0 restoration), and floodplain width/Manning's n. Stream restoration decreased (attenuated) peak flow up to 37% and increased floodplain exchange by up to 46%. Floodplain width and % channel restored had the largest impact on flood attenuation. The incremental effects of new restoration projects on flood attenuation were greatest when little prior restoration had occurred. By contrast, incremental effects on floodplain exchange were greatest in the presence of substantial prior restoration, setting up a tradeoff. A similar tradeoff was revealed between attenuation and exchange for project location, but not bank height or floodplain width. In particular, attenuation and exchange were always greater for Stage 0 than for bankfull floodplain restoration. Stage 0 thus may counteract human impacts such as urbanization.