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HomeMy WebLinkAbout1990-10-03 - AGENDA REPORTS - DRAINAGE FLOOD CONTROL (2)PRESENTATION DATE: October 3, 1990 SUBJECT: DEPARTMENT: Public Works BACKGROUND AGENDA REPORT City Manager Approval Item to be presented John E. Medina The Council has previously expressed concerns regarding drainage and flooding. These concerns focus on flooding in areas which are within natural, unimproved drainage courses such as Placerita Canyon, Sand Canyon; etc. Not only are these areas subject to flooding under natural conditions, but problems can arise from continued development within these flood plains without a comprehensive plan to address these concerns. In order to deal with the flooding issue in these areas, a comprehensive plan is necessary. The plan can be easily prepared once certain policy decisions have been made. Currently, the plans for dealing with flood control are to provide concrete lined soft bottom channels. However, there has been some expression by local groups that a more natural channel would be desirable. A natural channel could be designed within these canyon floodways. These can be as simple as graded side slopes or pipe and wire revetment. The disadvantage of these more natural type improvements, is that the area necessary for the floodway must be three to four times wider than one which would have slide slopes improved with either gunite or concrete. As an example, the channel in Sand Canyon could be as little as 100 feet wide, if it were improved with concrete side slopes. If a more natural channel is desired, it would be in excess of 400 feet wide and reduce the amount of area that could be developed. In some cases, development has already infringed within that floodway area. Not only is the channel wider, but it is also more difficult to protect adjacent areas from erosion from a major storm. It is the continuous erosion and deposition of debris from storms that are the greatest challenge in predicting and controlling floodwaters in a natural channel. A more serviceable: approach would be the construction of channels with concrete lining along the sides and natural channel bottoms. In this way, the property in these 4ighly desirable canyon areas can be developed and yet protected from floodwaters. It is a more expensive approach than simply a natural channel but has greater protection possibilities. It also would permit passive recreational uses such as bike lanes and equestrian trails within the natural channel bottom during dry weather periods. Agenda Item:_____. Once the policy decision is made regarding the nature of the channel design, then the cost and who will pay for these improvements can be addressed. Since the passage of Proposition 13, it has been very difficult, if not impossible to pass general obligation bonds which was a classical approach to constructing flood control improvements. Assessment districts are a means by which a City can assess those properties that will benefit from these improvements. However, the cost for those benefitting properties is so great that assessment districts have had little success in getting these needed channel improvements. One method which has been used successfully in many areas is a drainage improvement fee assessed on all new development. The City currently is in the process of hiring a consultant to review many of the City's needed infrastructure improvements, one of which will be flood control. If such a fee were established, it would be as a contribution to an assessment district which would help significantly reduce the cost to those properties within these canyon areas that would benefit from the improvements. In summary, Council needs to make certain policy decisions regarding the treatment of flood control improvements. Once this is established, the Public Works staff can develop plans which will incorporate those policy decisions in a total floodway improvement program. The initial step to accomplish this task would be the preparation of a master plan of drainage. The master plan would focus on specific drainage areas to determine the size, magnitude, and cost of these improvements. After this is done, we can suggest a number of financing mechanisms such as assessment districts, drainage fee districts, federal funds, etc. to implement the plan. We would suggest the Council give serious consideration and direction to staff to include the preparation of a Master Plan of Drainage in the Five Year Capital Improvement Program. Attached is a brief historical background of drainage and. flood control programs. These will provide additional information for the Council's edification. The City Council receive the report and provideanynecessary direction. ATTACHMENT Drainage/Flood Control Historical Perspective /ce DRAINAGE/FLOOD CONTROL HISTORICAL PERSPECTIVE Flood control and drainage have been addressed in the Santa Clarita Valley in a similar manner as most communities in the western United States. In the formative years, structures were not built in areas known to flood.In some instances, buildings are built in areas that may have not experienced flooding for years. As these areas became identified, they were mapped and buildings were not permitted there. These areas of natural flooding tend to be very wide and can meander over a half, mile wide drainage area. This factor makes it difficult to predict the exact location and character of the flood. As the community continues to develop, there are greater pressures to develop within those flood hazard -areas. This pressure to develop and the concerns regarding flooding, results in each community formulating a program to address the problem. The City of Santa Clarita has inherited a number of programs which provide methodologies and means to insure that proposed projects will not be subject to flood hazard and that the existing areas will not be impacted by this additional development. The City uses its Building Code, the Federal Flood Insurance Program, and a Flood Control District to deal with drainage and flooding concerns relating to development and the protection of.existing properties. BUILDING CODE On an individual basis, any single building that is proposed to be constructed. within the City requires a building permit. In this permit process the Building Code does permit the City to refuse a permit if it is determined that the structure would be subject to flood hazard. It should be pointed out that the nature of the concerns are for the structure itself and not for the property. In other words, this method would insure that the structure, its contents and residents are reasonably free from flood hazard. It does not ensure that there may not be flood waters running across the property which may make it difficult on rare occasions to cross the property. FEDERAL FLOOD INSURANCE PROGRAM The Federal Flood Insurance Program was enacted by Congress to deal with disasters caused by floods. Each time a flood impacted an area in the United States, Congress was asked to appropriate monies from its budget 'to repay residents and rebuild those areas that were damaged. It was apparent that many of these areas took no cognizance of the fact that flood waters occurred and simply allowed residents to build structures in these flood hazard areas. Congress felt that a more effective program would be one that required all communities to map the flood hazard. areas, deny building permits unless adequate flood protection was provided, and to develop a pool of money similar to most insurance programs which would provide the necessary funds to repay for damages. These funds, of course, would be paid by those citizens who secured flood insurance. The means by which this was enforced is that lending institutions that were insured by the Federal Government were required to determine whether the property was subject to flood hazard, and if it was, to require that flood insurance be secured through proper insurance carriers. Shortly after incorporation, the City did provide the necessary enabling ordinances to enter into the flood insurance program which allowed its citizens to secure the necessary insurance and provided_ yet another mechanism to address structures in flood prone areas. FLOOD CONTROL DISTRICT The third program dealing with flood control issues resulted with the establishment of the Los Angeles County Flood Control District. The District was a special district established by State statutes to deal with a specific purpose - flooding. Flooding does not respect jurisdictional boundaries and therefore a special district which can encompass numerous jurisdictions is an effective way of dealing with flood control. For many years the Flood Control District established programs to construct major flood control systems. These systems included dams, retention basins, major river channels, culverts, and storm drains. In addition to that our street system provides a major.network to carry floodwaters within a drainage area until it enters a point of collection, generally a catch basin. The funds to develop these systems were general obligation bonds. These required. only a 50% majority vote and were generally approved by the voters after major floods occurred. Since the passage of Proposition 13, and the requirement of a 2/3 majority vote, it has been extremely difficult to secure approval of general obligation bonds. The net result has been a curtailment in the construction of major flood control works within the district. The district currently assesses properties each year for maintenance of the system and generates approximately 28 million dollars to fund capital improvements. A priority is established for improvements throughout the entire district • and are constructed as funds become available. Currently, the district is providing funds for the construction of storm drain improvements in the vicinity of Live Oak Springs Canyon. Of course, the small amount of capital improvement funds does not allow any major flood control works to be constructed. The - shift has been to condition development to improve more of the system. CURRENT DEVELOPMENT PROCEDURES Individual developments as we indicated, simply protect the structure .from flood hazard, recognizing that.an individual dwelling does not contribute any significant increase in run-off. However, major developments with paved streets, smaller lots, and more concentrated development may change the drainage picture for that area. These projects are required to submit a hydrology study prior to approval. This study must show what the nature of the natural flow upgrade, through, and downgrade from the development. In other words, what is the undeveloped condition. Added to this is the expected increase in flow from the property to be development. This results in a comparison between what we would expect in the undeveloped condition and what additional flow we would expect in the developed condition. This is commonly referred to as a A Q . This -A Q is merely the increase, if any, of flow caused by the development itself. The development must deal with that increase in flow, either by constructing the necessary storm drains, providing. retention basins to keep the additional flow on-site, or to show that the nature of the development does not increase the amount of run-off. In addition, drainage flows that traverse the property must outlet in the same manner and at the same point as they would have had the property not been developed. The process is designed to permit development to occur without negatively impacting the development or upstream and downstream property owners. It should be recognized that this is based on a major capital storm and there may be increases in flow, particularly under minor storm conditions that may provide additional nuisance waters that currently did not occur off-site of the property. Again, as pointed out previously, the nature -of development in most cases does increase flow under these minor storm conditions. However, during major storms, properties are protected through the development process. I, Since incorporation there has been some policy decisions by the City Council to address the improvements in major floodways. Passive recreation areas, bike lanes, and equestrian trails are considered for inclusion in project improvements. This allows shared use of a floodway which, under the majority of conditions remains dry and can be used for other purposes, yet can carry significant amounts of water during a major flood. Staff has received considerable input from residents and the Council regarding accelerated programs to improve our existing floodways. We have discussed this with representatives from the Flood Control District and have looked at the City's Five Year Capital Improvement Program to incorporate a systematic approach to the improvements required. Of course the drawback in any of these schemes is the availability of.funds. There are a number of funding mechanisms such as assessment districts that could be used to fund improvements. These would permit long-term financing of major flood control improvements. The cost of those improvements would be paid by the properties benefitting from them. Major areas of concern include Sand Canyon, Iron Canyon, Placerita Canyon and the areas in upper Mint Canyon and Oak Spring Canyon. Of course these projects will continue to compete with other City funds and must be supported by the residents who will be paying for these improvements. We continue to look for opportunities to finance and provide the necessary improvements. In the interim, a current drainage and flood control review of project developments as outlined. above provides a means, to allow development to continue without increasing the effect on new projects or existing residents. Ultimately, we will have a system which will provide for the protection throughout the City of Santa Clarita, however, this is not something that can happen overnight. We see It as a long-term process being dovetailed with the development as envisioned in the City's General Plan. This is a condensed overview of the subject of drainage. Staff will be presenting the subject in further detail at this meeting. We would like the Council's reaction to this approach and any suggestions or direction on the. matter. RK:ce